W3C

XSL Transformations (XSLT) Version 3.0

W3C Last Call Working Draft 12 December 2013

This version:
http://www.w3.org/TR/2013/WD-xslt-30-20131212/
Latest version:
http://www.w3.org/TR/xslt-30/
Previous versions:
http://www.w3.org/TR/2012/WD-xslt-30-20120710/
http://www.w3.org/TR/2010/WD-xslt-21-20100511/
Editor:
Michael Kay, Saxonica <http://www.saxonica.com/>

See also translations.

The following associated resources are available:


Abstract

This specification defines the syntax and semantics of XSLT 3.0, a language for transforming XML documents into other XML documents.

XSLT 3.0 is a revised version of the XSLT 2.0 Recommendation [XSLT 2.0] published on 23 January 2007.

The primary purpose of the changes in this version of the language is to enable transformations to be performed in streaming mode, where neither the source document nor the result document is ever held in memory in its entirety. Another important aim is to improve the modularity of large stylesheets, allowing stylesheets to be developed from independently-developed components with a high level of software engineering robustness.

XSLT 3.0 is designed to be used in conjunction with XPath 3.0, which is defined in [XPath 3.0]. XSLT shares the same data model as XPath 3.0, which is defined in [Data Model], and it uses the library of functions and operators defined in [Functions and Operators]. XPath 3.0 and the underlying function library introduce a number of enhancements, for example the availability of higher-order functions. Some of the functions that were previously defined in the XSLT 2.0 specification, such as the format-dateFO30 and format-numberFO30 functions, are now defined in the standard function library to make them available to other host languages.

XSLT 3.0 also includes optional facilities to serialize the results of a transformation, by means of an interface to the serialization component described in [XSLT and XQuery Serialization].

This document contains hyperlinks to specific sections or definitions within other documents in this family of specifications. These links are indicated visually by a superscript identifying the target specification: for example XP30 for XPath 3.0, DM30 for the XDM data model version 3.0, FO30 for Functions and Operators version 3.0.

Status of this Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

This is a Last Call Working Draft as described in the W3C process document. It has been developed by the W3C XSLT Working Group, which is part of the XML Activity. Comments on this document will be formally accepted until 10 February 2014. The Working Group expects to advance this specification to Recommendation Status.

This specification has been developed in conjunction with [XPath 3.0] and other documents that underpin both XSLT and XQuery. XSLT 3.0 is dependent on XPath 3.0, which at the time of publication is a Proposed Recommendation.

In addition, this document specifies extensions to the XDM data model and to XPath language syntax to underpin the introduction of maps, which have been found necessary to support some XSLT streaming use cases and make many other processing tasks easier. This has involved extensive consultation with the XQuery Working Group (which has joint responsibility for XDM and XPath), and plans for incorporation of these extensions in a future version of those specifications are well advanced. This has resulted in some changes since the previous draft of July 2012: most notably, the := separator in map expressions has changed to :, and collations as a property of a map have been replaced by an alternative design using explicit collation keys.

Changes since previous versions are listed in J Changes since XSLT 2.0 and K Changes since the Working Draft of 10 July 2012. The only incompatibilities with XSLT 2.0 relate to the way in which certain error conditions are handled: the details are given in L Incompatibilities with XSLT 2.0. The most significant changes since the previous working draft are the introduction of text value templates and static variables; the introduction of a family of URIs for collations conforming to the Unicode Collation Algorithm; extensive reworking of the syntax for patterns; changes to the way in which accumulator functions are invoked; and a substantial rewrite of the rules for assessing the streamability of stylesheet constructs such as template rules.

Please report errors in this document using W3C's public Bugzilla system (instructions can be found at http://www.w3.org/XML/2005/04/qt-bugzilla). If access to that system is not feasible, you may send your comments to the W3C XSLT/XPath/XQuery public comments mailing list, public-qt-comments@w3.org. It will be very helpful if you include the string "[XSLT30]" in the subject line of your report, whether made in Bugzilla or in email. Please use multiple Bugzilla entries (or, if necessary, multiple email messages) if you have more than one comment to make. Archives of the comments and responses are available at http://lists.w3.org/Archives/Public/public-qt-comments/.

A public test suite for XSLT 3.0 is under development. Implementors and others are encouraged to run these tests, to submit comments and contributions, and to report their results. The test suite is available at https://dvcs.w3.org/hg/xslt30-test/.

Publication as a Last Call Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

Table of Contents

1 Introduction
    1.1 What is XSLT?
    1.2 What's New in XSLT 3.0?
2 Concepts
    2.1 Terminology
    2.2 Notation
    2.3 Initiating a Transformation
        2.3.1 Information needed for Static Analysis
        2.3.2 Priming a Stylesheet
        2.3.3 Invoking an Initial Mode
        2.3.4 Invoking an Initial Template
        2.3.5 Invoking an Initial Function
        2.3.6 Post-processing the Raw Result
    2.4 Executing a Transformation
    2.5 The Evaluation Context
    2.6 Parsing and Serialization
    2.7 Packages and Modules
    2.8 Extensibility
    2.9 Stylesheets and XML Schemas
    2.10 Streaming
    2.11 Error Handling
3 Stylesheet Structure
    3.1 XSLT Namespace
    3.2 Reserved Namespaces
    3.3 Extension Attributes
    3.4 XSLT Media Type
    3.5 Standard Attributes
    3.6 Packages
        3.6.1 Dependencies between Packages
        3.6.2 Named Components in Packages
            3.6.2.1 Visibility of Components
            3.6.2.2 Visibility of Declarations
            3.6.2.3 Exposing Components
            3.6.2.4 Accepting Components
            3.6.2.5 Overriding Named Components from a Used Package
            3.6.2.6 Binding References to Components
        3.6.3 Overriding Template Rules from a Used Package
        3.6.4 Declarations Local to a Package
        3.6.5 Using an XQuery Library Package
    3.7 Stylesheet Modules
    3.8 Stylesheet Element
        3.8.1 The default-collation Attribute
        3.8.2 The [xsl:]default-mode Attribute
        3.8.3 User-defined Data Elements
    3.9 Simplified Stylesheet Modules
    3.10 Backwards Compatible Processing
        3.10.1 XSLT 1.0 Compatibility Mode
        3.10.2 XSLT 2.0 Compatibility Mode
    3.11 Forwards Compatible Processing
    3.12 Combining Stylesheet Modules
        3.12.1 Locating Stylesheet Modules
        3.12.2 Stylesheet Inclusion
        3.12.3 Stylesheet Import
    3.13 Embedded Stylesheet Modules
    3.14 Conditional Element Inclusion
    3.15 Built-in Types
    3.16 Importing Schema Components
4 Data Model
    4.1 XML Versions
    4.2 Stripping Whitespace from the Stylesheet
    4.3 Stripping Type Annotations from a Source Tree
    4.4 Stripping Whitespace from a Source Tree
    4.5 Attribute Types and DTD Validation
    4.6 Data Model for Streaming
    4.7 Limits
    4.8 Disable Output Escaping
5 Features of the XSLT Language
    5.1 Qualified Names
    5.2 Unprefixed Lexical QNames in Expressions and Patterns
    5.3 Expressions
    5.4 The Static and Dynamic Context
        5.4.1 Initializing the Static Context
        5.4.2 Additional Static Context Components used by XSLT
        5.4.3 Initializing the Dynamic Context
            5.4.3.1 Maintaining Position: the Focus
            5.4.3.2 Other Components of the XPath Dynamic Context
        5.4.4 Additional Dynamic Context Components used by XSLT
    5.5 Defining a Decimal Format
    5.6 Patterns
        5.6.1 Examples of Patterns
        5.6.2 Syntax of Patterns
        5.6.3 The Meaning of a Pattern
        5.6.4 Errors in Patterns
    5.7 Value Templates
        5.7.1 Attribute Value Templates
        5.7.2 Text Value Templates
    5.8 Sequence Constructors
        5.8.1 Constructing Complex Content
        5.8.2 Constructing Simple Content
        5.8.3 Namespace Fixup
    5.9 URI References
6 Template Rules
    6.1 Defining Templates
    6.2 Defining Template Rules
    6.3 Applying Template Rules
    6.4 Conflict Resolution for Template Rules
    6.5 Default Priority for Template Rules
    6.6 Modes
        6.6.1 Declaring Modes
        6.6.2 Using Modes
        6.6.3 Streamable Templates
    6.7 Declaring the Context Item
        6.7.1 Declaring the Initial Context Item for a Mode
        6.7.2 Declaring the context item for a template
    6.8 Built-in Template Rules
        6.8.1 Built-in Templates: Text-only Copy
        6.8.2 Built-in Templates: Deep Copy
        6.8.3 Built-in Templates: Shallow Copy
        6.8.4 Built-in Templates: Deep Skip
        6.8.5 Built-in Templates: Shallow Skip
        6.8.6 Built-in Templates: Fail
    6.9 Overriding Template Rules
    6.10 Passing Parameters to Template Rules
7 Repetition
    7.1 The xsl:for-each instruction
    7.2 The xsl:iterate Instruction
8 Conditional Processing
    8.1 Conditional Processing with xsl:if
    8.2 Conditional Processing with xsl:choose
    8.3 Try/Catch
        8.3.1 Try/Catch Examples
9 Variables and Parameters
    9.1 Variables
    9.2 Parameters
    9.3 Values of Variables and Parameters
    9.4 Creating Implicit Document Nodes
    9.5 Global Variables and Parameters
    9.6 Static Variables and Parameters
    9.7 Static Expressions
    9.8 Local Variables and Parameters
    9.9 Scope of Variables
    9.10 Setting Parameter Values
    9.11 Circular Definitions
10 Callable Components
    10.1 Named Templates
        10.1.1 Passing Parameters to Named Templates
        10.1.2 Tunnel Parameters
    10.2 Named Attribute Sets
        10.2.1 Using Attribute Sets
        10.2.2 Visibility of Attribute Sets
        10.2.3 Streamability of Attribute Sets
        10.2.4 Evaluating Attribute Sets
        10.2.5 Attribute Sets: Examples
    10.3 Stylesheet Functions
        10.3.1 Function Name and Arity
        10.3.2 Arguments
        10.3.3 Function Result
        10.3.4 Visibility and Overriding of Functions
        10.3.5 Dynamic Access to Functions
        10.3.6 Determinism of Functions
        10.3.7 Memoization
        10.3.8 Examples of Stylesheet Functions
    10.4 Dynamic XPath Evaluation
        10.4.1 Static context for the target expression
        10.4.2 Dynamic context for the target expression
        10.4.3 The effect of the xsl:evaluate instruction
        10.4.4 xsl:evaluate as an optional feature
        10.4.5 Examples of xsl:evaluate
11 Creating Nodes and Sequences
    11.1 Literal Result Elements
        11.1.1 Setting the Type Annotation for Literal Result Elements
        11.1.2 Attribute Nodes for Literal Result Elements
        11.1.3 Namespace Nodes for Literal Result Elements
        11.1.4 Conditional Creation of Literal Result Elements
        11.1.5 Namespace Aliasing
    11.2 Creating Element Nodes Using xsl:element
        11.2.1 The Content of the Constructed Element Node
        11.2.2 The Name of the Constructed Element Node
        11.2.3 Other Properties of the Constructed Element Node
        11.2.4 The Type Annotation of the Constructed Element Node
        11.2.5 Conditional Construction of Element Nodes
    11.3 Creating Attribute Nodes Using xsl:attribute
        11.3.1 Setting the Type Annotation for a Constructed Attribute Node
        11.3.2 Conditional Creation of Attribute Nodes
    11.4 Creating Text Nodes
        11.4.1 Literal Text Nodes
        11.4.2 Creating Text Nodes Using xsl:text
        11.4.3 Generating Text with xsl:value-of
    11.5 Creating Document Nodes
    11.6 Creating Processing Instructions
    11.7 Creating Namespace Nodes
    11.8 Creating Comments
    11.9 Copying Nodes
        11.9.1 Shallow Copy
            11.9.1.1 Conditional Copying of Nodes
        11.9.2 Deep Copy
    11.10 Constructing Sequences
12 Numbering
    12.1 Formatting a Supplied Number
    12.2 Numbering based on Position in a Document
    12.3 Number to String Conversion Attributes
13 Sorting
    13.1 The xsl:sort Element
        13.1.1 The Sorting Process
        13.1.2 Comparing Sort Key Values
        13.1.3 Sorting Using Collations
    13.2 Creating a Sorted Sequence
    13.3 Processing a Sequence in Sorted Order
    13.4 The Unicode Collation Algorithm
14 Grouping
    14.1 The xsl:for-each-group Element
    14.2 Accessing Information about the Current Group Value
        14.2.1 fn:current-group
        14.2.2 fn:current-grouping-key
    14.3 Ordering among Groups
    14.4 Examples of Grouping
    14.5 Non-Transitivity
15 Merging
    15.1 Terminology for Merging
    15.2 The xsl:merge Instruction
    15.3 Selecting the Sequences to be Merged
    15.4 Streamable Merging
    15.5 Defining the Merge Keys
    15.6 The xsl:merge-action Element
    15.7 Examples of xsl:merge
16 Splitting
    16.1 The xsl:fork Instruction
    16.2 Examples of Splitting with Streamed Data
17 Regular Expressions
    17.1 The xsl:analyze-string Instruction
    17.2 fn:regex-group
    17.3 Examples of Regular Expression Matching
18 Streaming
    18.1 The xsl:stream Instruction
        18.1.1 Validation of Streamed Documents
        18.1.2 Examples of xsl:stream
    18.2 Accumulators
        18.2.1 Declaring an Accumulator
        18.2.2 Informal Model for Accumulators
        18.2.3 Formal Model for Accumulators
        18.2.4 fn:accumulator-before
        18.2.5 fn:accumulator-after
        18.2.6 Visibility and Overriding of Accumulators
        18.2.7 Streamability of Accumulators
        18.2.8 Examples of Accumulators
    18.3 fn:copy-of
    18.4 fn:snapshot
19 Streamability
    19.1 An Optimization: Pattern-Based Scanning
    19.2 Determining the Static Type of a Construct
    19.3 Determining the Context Item Type
    19.4 Operand Roles
        19.4.1 Examples showing the Effect of Operand Usage
    19.5 Determining the Posture of a Construct
    19.6 Determining the Context Posture
    19.7 The Sweep of a Construct
    19.8 Classifying Constructs
        19.8.1 General Rules for Streamability
        19.8.2 Examples of the General Streamability Rules
        19.8.3 Classifying Sequence Constructors
        19.8.4 Classifying Instructions
            19.8.4.1 Streamability of Literal Result Elements
            19.8.4.2 Streamability of extension instructions
            19.8.4.3 Streamability of xsl:analyze-string
            19.8.4.4 Streamability of xsl:apply-imports
            19.8.4.5 Streamability of xsl:apply-templates
            19.8.4.6 Streamability of xsl:assert
            19.8.4.7 Streamability of xsl:attribute
            19.8.4.8 Streamability of xsl:break
            19.8.4.9 Streamability of xsl:call-template
            19.8.4.10 Streamability of xsl:choose
            19.8.4.11 Streamability of xsl:comment
            19.8.4.12 Streamability of xsl:copy
            19.8.4.13 Streamability of xsl:copy-of
            19.8.4.14 Streamability of xsl:document
            19.8.4.15 Streamability of xsl:element
            19.8.4.16 Streamability of xsl:evaluate
            19.8.4.17 Streamability of xsl:for-each
            19.8.4.18 Streamability of xsl:for-each-group
            19.8.4.19 Streamability of xsl:fork
            19.8.4.20 Streamability of xsl:if
            19.8.4.21 Streamability of xsl:iterate
            19.8.4.22 Streamability of xsl:map
            19.8.4.23 Streamability of xsl:map-entry
            19.8.4.24 Streamability of xsl:merge
            19.8.4.25 Streamability of xsl:message
            19.8.4.26 Streamability of xsl:namespace
            19.8.4.27 Streamability of xsl:next-iteration
            19.8.4.28 Streamability of xsl:next-match
            19.8.4.29 Streamability of xsl:number
            19.8.4.30 Streamability of xsl:perform-sort
            19.8.4.31 Streamability of xsl:processing-instruction
            19.8.4.32 Streamability of xsl:result-document
            19.8.4.33 Streamability of xsl:sequence
            19.8.4.34 Streamability of xsl:stream
            19.8.4.35 Streamability of xsl:text
            19.8.4.36 Streamability of xsl:try
            19.8.4.37 Streamability of xsl:value-of
            19.8.4.38 Streamability of xsl:variable
        19.8.5 Classifying Attribute Sets
        19.8.6 Classifying Value Templates
        19.8.7 Classifying Expressions
            19.8.7.1 Streamability of for expressions
            19.8.7.2 Streamability of Quantified Expressions
            19.8.7.3 Streamability of if expressions
            19.8.7.4 Streamability of union, intersect, and except expressions
            19.8.7.5 Streamability of Simple Mapping Expressions
            19.8.7.6 Streamability of Path Expressions
            19.8.7.7 Streamability of Axis Steps
            19.8.7.8 Streamability of Filter Expressions
            19.8.7.9 Streamability of Dynamic Function Calls
            19.8.7.10 Streamability of Variable References
            19.8.7.11 Streamability of the Context Item Expression
            19.8.7.12 Streamability of Function Calls
            19.8.7.13 Streamability of Named Function References
            19.8.7.14 Streamability of Inline Function Declarations
            19.8.7.15 Streamability of map expressions
        19.8.8 Classifying Calls to Built-In Functions
            19.8.8.1 Streamability of the accumulator-after function
            19.8.8.2 Streamability of the accumulator-before function
            19.8.8.3 Streamability of the current function
            19.8.8.4 Streamability of the current-group function
            19.8.8.5 Streamability of the current-grouping-key function
            19.8.8.6 Streamability of the function-lookup function
            19.8.8.7 Streamability of the last function
            19.8.8.8 Streamability of the outermost function
            19.8.8.9 Streamability of the position function
            19.8.8.10 Streamability of the root function
            19.8.8.11 Streamability of the unparsed-entity-public-id function
            19.8.8.12 Streamability of the unparsed-entity-uri function
        19.8.9 Classifying Patterns
    19.9 Examples of Streamability Analysis
    19.10 Streamability Guarantees
20 Additional Functions
    20.1 fn:document
    20.2 Keys
        20.2.1 The xsl:key Declaration
        20.2.2 fn:key
    20.3 Miscellaneous Additional Functions
        20.3.1 fn:current
        20.3.2 fn:unparsed-entity-uri
        20.3.3 fn:unparsed-entity-public-id
        20.3.4 fn:system-property
21 XPath Extensions
    21.1 Maps
        21.1.1 The Type of a Map
        21.1.2 Functions that Operate on Maps
            21.1.2.1 map:new
            21.1.2.2 map:keys
            21.1.2.3 map:contains
            21.1.2.4 map:get
            21.1.2.5 map:entry
            21.1.2.6 map:remove
            21.1.2.7 map:for-each-entry
            21.1.2.8 fn:collation-key
            21.1.2.10 fn:deep-equal
        21.1.3 Map Instructions
        21.1.4 Map Expressions
        21.1.5 Maps and Streaming
        21.1.6 Examples using Maps
    21.2 Processing JSON Data
        21.2.1 XML Representation of JSON
        21.2.2 fn:json-to-xml
        21.2.3 Converting XML to JSON
22 Diagnostics
    22.1 Messages
    22.2 Assertions
23 Extensibility and Fallback
    23.1 Extension Functions
        23.1.1 fn:function-available
        23.1.2 Calling Extension Functions
        23.1.3 External Objects
        23.1.4 fn:type-available
    23.2 Extension Instructions
        23.2.1 Designating an Extension Namespace
        23.2.2 fn:element-available
        23.2.3 Fallback
24 Final Result Trees
    24.1 Creating Final Result Trees
    24.2 Validation
        24.2.1 Validating Constructed Elements and Attributes
            24.2.1.1 Validation using the [xsl:]validation Attribute
            24.2.1.2 Validation using the [xsl:]type Attribute
            24.2.1.3 The Validation Process
        24.2.2 Validating Document Nodes
25 Serialization
    25.1 Character Maps
    25.2 Disabling Output Escaping
26 Conformance
    26.1 Basic XSLT Processor
    26.2 Schema-Awareness Conformance Feature
    26.3 Serialization Feature
    26.4 Compatibility Features
    26.5 Streaming Feature
    26.6 Dynamic Evaluation Feature
    26.7 XQuery Invocation Feature

Appendices

A References
    A.1 Normative References
    A.2 Other References
B XML Representation of JSON
    B.1 Schema for the XML Representation of JSON
    B.2 Stylesheet for converting XML to JSON (without indentation)
    B.3 Stylesheet for converting XML to JSON (with indentation)
C Glossary (Non-Normative)
D Element Syntax Summary (Non-Normative)
E Summary of Error Conditions (Non-Normative)
F Checklist of Implementation-Defined Features (Non-Normative)
G List of XSLT-defined functions (Non-Normative)
H Schema for XSLT Stylesheets (Non-Normative)
I Acknowledgements (Non-Normative)
J Changes since XSLT 2.0 (Non-Normative)
    J.1 Changes in this Specification
    J.2 Changes in Other Related Specifications
K Changes since the Working Draft of 10 July 2012 (Non-Normative)
L Incompatibilities with XSLT 2.0 (Non-Normative)


1 Introduction

1.1 What is XSLT?

This specification defines the syntax and semantics of the XSLT 3.0 language.

[Definition: A transformation in the XSLT language is expressed in the form of a stylesheet, whose syntax is well-formed XML [XML 1.0] conforming to the Namespaces in XML Recommendation [Namespaces in XML].]

A stylesheet generally includes elements that are defined by XSLT as well as elements that are not defined by XSLT. XSLT-defined elements are distinguished by use of the namespace http://www.w3.org/1999/XSL/Transform (see 3.1 XSLT Namespace), which is referred to in this specification as the XSLT namespace. Thus this specification is a definition of the syntax and semantics of the XSLT namespace.

The term stylesheet reflects the fact that one of the important roles of XSLT is to add styling information to an XML source document, by transforming it into a document consisting of XSL formatting objects (see [XSL-FO]), or into another presentation-oriented format such as HTML, XHTML, or SVG. However, XSLT is used for a wide range of transformation tasks, not exclusively for formatting and presentation applications.

A transformation expressed in XSLT describes rules for transforming zero or more source trees into one or more result trees. The structure of these trees is described in [Data Model]. The transformation is achieved by a set of template rules. A template rule associates a pattern, which matches nodes in the source document, with a sequence constructor. In many cases, evaluating the sequence constructor will cause new nodes to be constructed, which can be used to produce part of a result tree. The structure of the result trees can be completely different from the structure of the source trees. In constructing a result tree, nodes from the source trees can be filtered and reordered, and arbitrary structure can be added. This mechanism allows a stylesheet to be applicable to a wide class of documents that have similar source tree structures.

Note:

The use of the term tree in this document does not imply the use of a data structure in memory that holds the entire contents of the document at one time. It implies rather a logical view of the XML input and output in which elements have a hierarchic relationship to each other. When a source document is being processed in a streaming manner, access to the nodes in this tree is constrained, but it is still viewed and described as a tree.

A stylesheet has a modular structure. It may consist of one or more packages developed independently of each other; each package defines the services (functions, templates, etc) that it exposes to its clients. Internally, a package may consist of a number of stylesheet modules.

[Definition: For a given transformation, one stylesheet module functions as the principal stylesheet module. The complete stylesheet is assembled by finding the stylesheet modules referenced directly or indirectly from the principal stylesheet module using xsl:include and xsl:import elements: see 3.12.2 Stylesheet Inclusion and 3.12.3 Stylesheet Import.]

1.2 What's New in XSLT 3.0?

A major focus for enhancements in XSLT 3.0 is the requirement to enable streaming of source documents. This is needed when source documents become too large to hold in main memory, and also for applications where it is important to start delivering results before the entire source document is available.

While implementations of XSLT that use streaming have always been theoretically possible, the nature of the language has made it very difficult to achieve this in practice. The approach adopted in this specification is twofold: it identifies a set of restrictions which, if followed by stylesheet authors, will enable implementations to adopt a streaming mode of operation without placing excessive demands on the optimization capabilities of the processor; and it provides new constructs to indicate that streaming is required, or to express transformations in a way that makes it easier for the processor to adopt a streaming execution plan.

Capabilities provided in this category include:

  • A new xsl:stream instruction, which reads and processes a source document in streaming mode;

  • The ability to declare that a mode is a streaming mode, in which case all the template rules using that mode must be streamable;

  • A new xsl:iterate instruction, which iterates over the items in a sequence, allowing parameters for the processing of one item to be set during the processing of the previous item;

  • A new xsl:merge instruction, allowing multiple input streams to be merged into a single output stream;

  • A new xsl:fork instruction, allowing multiple computations to be performed in parallel during a single pass through an input document.

  • Accumulators, which allow a value to be computed progressively during streamed processing of a document, and accessed as a function of a node in the document, without compromise to the functional nature of the XSLT language.

A second focus for enhancements in XSLT 3.0 is the introduction of a new mechanism for stylesheet modularity, called the package. Unlike the stylesheet modules of XSLT 1.0 and 2.0 (which remain available), a package defines an interface that regulates which functions, variables, templates and other components are visible outside the package, and which can be overridden. There are two main goals for this facility: it is designed to deliver software engineering benefits by improving the reusability and maintainability of code, and it is intended to streamline stylesheet deployment by allowing packages to be compiled independently of each other, and compiled instances of packages to be shared between multiple applications.

Other significant features in XSLT 3.0 include:

  • An xsl:evaluate instruction allowing evaluation of XPath expressions that are dynamically constructed as strings, or that are read from a source document;

  • Enhancements to the syntax of patterns, in particular enabling the matching of atomic values as well as nodes;

  • An xsl:try instruction to allow recovery from dynamic errors;

  • The element xsl:context-item, used to declare the stylesheet's expectations of the initial context item (notably, its type), given the initial mode.

  • A new instruction xsl:assert to assist developers in producing correct and robust code.

XSLT 3.0 also delivers enhancements made to the XPath language and to the standard function library, including the following:

  • Variables can now be bound in XPath using the let expression.

  • Functions are now first class values, and can be passed as arguments to other (higher-order) functions, making XSLT a fully-fledged functional programming language.

  • A number of new functions are available, for example trigonometric functions, and the functions parse-xmlFO30 and serializeFO30 to convert between lexical and tree representations of XML.

This Working Draft includes support for maps (a data structure consisting of key/value pairs, sometimes referred to in other programming languages as dictionaries, hashes, or associative arrays). This feature extends the data model, provides new syntax in XPath, and adds a number of new functions and operators. The XSL Working Group intends that these changes should eventually become part of XPath: however, this has not yet been agreed with all interested parties.

A full list of changes is at J Changes since XSLT 2.0.

2 Concepts

2.1 Terminology

For a full glossary of terms, see C Glossary.

[Definition: The software responsible for transforming source trees into result trees using an XSLT stylesheet is referred to as the processor. This is sometimes expanded to XSLT processor to avoid any confusion with other processors, for example an XML processor.]

[Definition: A specific product that performs the functions of an XSLT processor is referred to as an implementation. ]

[Definition: The term result tree is used to refer to any tree constructed by instructions in the stylesheet. A result tree is either a final result tree or a temporary tree.]

[Definition: A final result tree is a result tree that forms part of the final output of a transformation. Once created, the contents of a final result tree are not accessible within the stylesheet itself.] The xsl:result-document instruction always creates a final result tree, and a final result tree may also be created implicitly by the initial template. The conditions under which this happens are described in 2.4 Executing a Transformation. A final result tree may be serialized as described in 25 Serialization.

[Definition: The term source tree means any tree provided as input to the transformation. This includes the document containing the initial context item if any, documents containing nodes supplied as the values of stylesheet parameters, documents obtained from the results of functions such as document, docFO30, and collectionFO30, documents read using the xsl:stream instruction, and documents returned by extension functions or extension instructions. In the context of a particular XSLT instruction, the term source tree means any tree provided as input to that instruction; this may be a source tree of the transformation as a whole, or it may be a temporary tree produced during the course of the transformation.]

[Definition: The term temporary tree means any tree that is neither a source tree nor a final result tree.] Temporary trees are used to hold intermediate results during the execution of the transformation.

The use of the term "tree" in phrases such as source tree, result tree, and temporary tree is not confined to documents that the processor materializes in memory in their entirety. The processor may, and in some cases must, use streaming techniques to limit the amount of memory used to hold source and result documents. When streaming is used, the nodes of the tree may never all be in memory at the same time, but at an abstract level the information is still modeled as a tree of nodes, and the document is therefore still described as a tree.

In this specification the phrases must, must not, should, should not, may, required, and recommended, when used in normative text and rendered in capitals, are to be interpreted as described in [rfc2119].

Where the phrase must, must not, or required relates to the behavior of the XSLT processor, then an implementation is not conformant unless it behaves as specified, subject to the more detailed rules in 26 Conformance.

Where the phrase must, must not, or required relates to a stylesheet then the processor must enforce this constraint on stylesheets by reporting an error if the constraint is not satisfied.

Where the phrase should, should not, or recommended relates to a stylesheet then a processor may produce warning messages if the constraint is not satisfied, but must not treat this as an error.

[Definition: In this specification, the term implementation-defined refers to a feature where the implementation is allowed some flexibility, and where the choices made by the implementation must be described in documentation that accompanies any conformance claim.]

[Definition: The term implementation-dependent refers to a feature where the behavior may vary from one implementation to another, and where the vendor is not expected to provide a full specification of the behavior.] (This might apply, for example, to limits on the size of source documents that can be transformed.)

In all cases where this specification leaves the behavior implementation-defined or implementation-dependent, the implementation has the option of providing mechanisms that allow the user to influence the behavior.

A paragraph labeled as a Note or described as an example is non-normative.

Many terms used in this document are defined in the XPath specification [XPath 3.0] or the XDM specification [Data Model]. Particular attention is drawn to the following:

  • [Definition: The term atomization is defined in Section 2.4.2 Atomization XP30. It is a process that takes as input a sequence of items, and returns a sequence of atomic values, in which the nodes are replaced by their typed values as defined in [Data Model].] For some items (for example, elements with element-only content, and function items), atomization generates a dynamic error.

  • [Definition: The term typed value is defined in Section 5.15 typed-value Accessor DM30. Every node, other than an element whose type annotation identifies it as having element-only content, has a typed value. For example, the typed value of an attribute of type xs:IDREFS is a sequence of zero or more xs:IDREF values.]

  • [Definition: The term string value is defined in Section 5.13 string-value Accessor DM30. Every node has a string value. For example, the string value of an element is the concatenation of the string values of all its descendant text nodes.]

  • [Definition: The term XPath 1.0 compatibility mode is defined in Section 2.1.1 Static Context XP30. This is a setting in the static context of an XPath expression; it has two values, true and false. When the value is set to true, the semantics of function calls and certain other operations are adjusted to give a greater degree of backwards compatibility between XPath 3.0 and XPath 1.0.]

[Definition: The term core function means a function that is specified in [Functions and Operators] and that is in the standard function namespace.]

2.2 Notation

[Definition: An XSLT element is an element in the XSLT namespace whose syntax and semantics are defined in this specification.] For a non-normative list of XSLT elements, see D Element Syntax Summary.

In this document the specification of each XSLT element is preceded by a summary of its syntax in the form of a model for elements of that element type. A full list of all these specifications can be found in D Element Syntax Summary. The meaning of syntax summary notation is as follows:

  • An attribute that is required is shown with its name in bold. An attribute that may be omitted is shown with a question mark following its name.

  • An attribute that is deprecated is shown in a grayed font within square brackets.

  • The string that occurs in the place of an attribute value specifies the allowed values of the attribute. If this is surrounded by curly brackets ({...}), then the attribute value is treated as an attribute value template, and the string occurring within curly brackets specifies the allowed values of the result of evaluating the attribute value template. Alternative allowed values are separated by |. A quoted string indicates a value equal to that specific string. An unquoted, italicized name specifies a particular type of value.

    The types used are as follows:

    Type name Meaning
    string Any string
    expression An XPath expression
    pattern A pattern as described in 5.6 Patterns.
    sequence-type A SequenceTypeXP30 as defined in the XPath specification
    uri; uris A URI, for example a namespace URI or a collation URI; a whitespace-separated list of URIs
    qname A lexical QName as defined in 5.1 Qualified Names
    eqname; eqnames An EQName as defined in 5.1 Qualified Names; a whitespace-separated list of EQNames
    token; tokens A string containing no significant whitespace; a whitespace-separated list of such strings
    nmtoken; nmtokens A string conforming to the XML schema rules for the type xs:NMTOKEN; a whitespace-separated list of such strings.
    char A string comprising a single Unicode character
    integer An integer, that is a string in the lexical space of the schema type xs:integer
    decimal A decimal value, that is a string in the lexical space of the schema type xs:decimal
    ncname An unprefixed name: a string in the value space of the schema type xs:NCName
    prefix An xs:NCName representing a namespace prefix, which must be in scope for the element on which it appears
    id An xs:NCName used as a unique identifier for an element in the containing XML document

    Except where the set of allowed values of an attribute is specified using the italicized name string or char, leading and trailing whitespace in the attribute value is ignored. In the case of an attribute value template, this applies to the effective value obtained when the attribute value template is expanded.

  • Unless the element is required to be empty, the model element contains a comment specifying the allowed content. The allowed content is specified in a similar way to an element type declaration in XML; sequence constructor means that any mixture of text nodes, literal result elements, extension instructions, and XSLT elements from the instruction category is allowed; other-declarations means that any mixture of XSLT elements from the declaration category, other than xsl:import, is allowed, together with user-defined data elements.

  • The element is prefaced by comments indicating if it belongs to the instruction category or declaration category or both. The category of an element only affects whether it is allowed in the content of elements that allow a sequence constructor or other-declarations.

Example: Syntax Notation

This example illustrates the notation used to describe XSLT elements.

<!-- Category: instruction -->
<xsl:example-element
  select = expression
  debug? = { "yes" | "no" } >
  <!-- Content: ((xsl:variable | xsl:param)*, xsl:sequence) -->
</xsl:example-element>

This example defines a (non-existent) element xsl:example-element. The element is classified as an instruction. It takes a mandatory select attribute, whose value is an XPath expression, and an optional debug attribute, whose value must be either yes or no; the curly brackets indicate that the value can be defined as an attribute value template, allowing a value such as debug="{$debug}", where the variable debug is evaluated to yield "yes" or "no" at run-time.

The content of an xsl:example-element instruction is defined to be a sequence of zero or more xsl:variable and xsl:param elements, followed by an xsl:sequence element.

[ERR XTSE0010] It is a static error if an XSLT-defined element is used in a context where it is not permitted, if a required attribute is omitted, or if the content of the element does not correspond to the content that is allowed for the element.

Attributes are validated as follows. These rules apply to the value of the attribute after removing leading and trailing whitespace.

  • [ERR XTSE0020] It is a static error if an attribute (other than an attribute written using curly brackets in a position where an attribute value template is permitted) contains a value that is not one of the permitted values for that attribute.

  • [ERR XTDE0030] It is a dynamic error if the effective value of an attribute written using curly brackets, in a position where an attribute value template is permitted, is a value that is not one of the permitted values for that attribute. If the processor is able to detect the error statically (for example, when any XPath expressions within the curly brackets can be evaluated statically), then the processor may optionally signal this as a static error.

Special rules apply if the construct appears in part of the stylesheet that is processed with forwards compatible behavior: see 3.11 Forwards Compatible Processing.

[Definition: Some constructs defined in this specification are described as being deprecated. The use of this term implies that stylesheet authors should not use the construct, and that the construct may be removed in a later version of this specification.]

Note:

This working draft includes a non-normative XML Schema for XSLT stylesheet modules (see H Schema for XSLT Stylesheets). The syntax summaries described in this section are normative.

XSLT defines a set of standard functions which are additional to those defined in [Functions and Operators]. A list of these functions appears in G List of XSLT-defined functions. The signatures of these functions are described using the same notation as used in [Functions and Operators]. The names of many of these functions are in the standard function namespace.

2.3 Initiating a Transformation

This document does not specify any application programming interfaces or other interfaces for initiating a transformation. This section, however, describes the information that is supplied when a transformation is initiated. Except where otherwise indicated, the information is required.

The execution of a stylesheet necessarily involves two activities: static analysis and dynamic evaluation. Static analysis consists of those tasks that can be performed by inspection of the stylesheet alone, including the binding of static variables, the evaluation of [xsl:]use-when expressions (see 3.14 Conditional Element Inclusion), and detection of static errors. Dynamic evaluation consists of tasks which in general cannot be carried out until a source document is available.

Dynamic evaluation is further divided into two activities: priming the stylesheet, and invoking a selected component.

  • Priming the stylesheet provides the dynamic context for evaluation, and supplies all the information needed to establish the values of global variables.

  • Invoking a component (such as a template or function) causes evaluation of that template or function to produce a result, which is an arbitrary XDM value.

    [Definition: The result of invoking the selected component, after any required conversion to the declared result type of the component, is referred to as the raw result.]

    This raw result may optionally be post-processed to construct a result tree, to serialize the result, or both, as described in 2.3.6 Post-processing the Raw Result.

Implementations may allow static analysis and dynamic evaluation to be initiated independently, so that the cost of static analysis can be amortized over multiple transformations using the same stylesheet. Implementations may also allow priming of a stylesheet and invocation of components to be initiated independently, in which case a single act of priming the stylesheet may be followed by a series of independent component invocations. Although this specification does not require such a separation, this section distinguishes information that is needed before static analysis can proceed, information that is needed to prime the stylesheet, and information that is needed when invoking components.

The language is designed to allow the static analysis of each package to be performed independently of other packages, with only basic knowledge of the properties of components made available by used packages. Beyond this, the specification leaves it to implementations to decide how to organize this process. When packages are not used explicitly, the entire stylesheet is treated as a single package.

2.3.1 Information needed for Static Analysis

The following information is needed prior to static analysis of a package:

Conceptually, the output of the static analysis of a package is an object which might be referred to (without constraining the implementation) as a compiled package. Prior to dynamic evaluation, all the compiled packages needed for execution must be checked for consistency, and component references must be resolved. This process may be referred to, again without constraining the implementation, as linking.

2.3.2 Priming a Stylesheet

The information needed when priming a stylesheet is as follows:

  • A set (possibly empty) of values for non-static stylesheet parameters (see 9.5 Global Variables and Parameters). These values are available for use within expressions in the stylesheet. As a minimum, values must be supplied for any parameters declared with the attribute required="yes".

    A supplied value is converted if necessary to the declared type of the stylesheet parameter using the function conversion rules.

    Note:

    It is possible for static stylesheet parameters to be declared in any package, and stylesheet parameters in different packages might have the same name.

  • [Definition: An item that acts as the initial context item for the transformation. This item is accessible within the stylesheet as the initial value of the XPath expressions . (dot) and self::node(), as described in 5.4.3.1 Maintaining Position: the Focus ].

    The initial context item is potentially used when initializing global variables and parameters. If the initialization of any global variables or parameter depends on the context item, a dynamic error can occur if the context item is absent. It is implementation-defined whether this error occurs during priming of the stylesheet or subsequently when the variable is referenced; and it is implementation-defined whether the error occurs at all if the variable or parameter is never referenced. The error can be suppressed by use of xsl:try and xsl:catch within the initialization of the variable or parameter.

    If no initial context item is supplied, then the context item, context position, and context size will initially be absent, and the evaluation of any expression that references these values will result in a dynamic error. (Note that the initial context size and context position will always be 1 (one) when an initial context item is supplied, and will be absent if no initial context item is supplied).

  • A base output URI. [Definition:  The base output URI is a URI to be used as the base URI when resolving a relative URI reference allocated to a final result tree. If the transformation generates more than one final result tree, then typically each one will be allocated a URI relative to this base URI. ] The way in which a base output URI is established is implementation-defined.

  • A mechanism for obtaining a document node and a media type, given an absolute URI. The total set of available documents (modeled as a mapping from URIs to document nodes) forms part of the context for evaluating XPath expressions, specifically the docFO30 function. The XSLT document function additionally requires the media type of the resource representation, for use in interpreting any fragment identifier present within a URI Reference.

    Note:

    The set of documents that are available to the stylesheet is implementation-dependent, as is the processing that is carried out to construct a tree representing the resource retrieved using a given URI. Some possible ways of constructing a document (specifically, rules for constructing a document from an Infoset or from a PSVI) are described in [Data Model].

Once a stylesheet is primed, the values of global variables remain stable through all component invocations. In addition, priming a stylesheet creates an execution scopeFO30 during which the dynamic context and all function calls remain stable; for example two calls on the current-dateTimeFO30 function within an execution scope are defined to return the same result.

Parameters passed to the transformation by the client application when a stylesheet is primed are matched against stylesheet parameters (see 9.5 Global Variables and Parameters), not against the template parameters declared within the initial template.

[ERR XTDE0050] It is a dynamic error if a stylesheet declares a visible stylesheet parameter with required="yes" and no value for this parameter is supplied when the stylesheet is primed. A stylesheet parameter is visible if it is not masked by another global variable or parameter with the same name and higher import precedence. If the parameter is a static parameter then the value must be supplied prior to the static analysis phase.

2.3.3 Invoking an Initial Mode

When the stylesheet is evaluated by invoking a mode, processing proceeds by finding the template rules that match the items in a supplied input sequence, and evaluating these template rules with a focus based on this input sequence.

The following information is needed when dynamic evaluation is to start with a template rule:

  • Optionally, a sequence of items to be processed. If no input sequence is supplied explicitly, this defaults to a singleton sequence containing the initial context item.

    Note:

    In earlier versions of this specification, the initial input sequence (to which templates are applied) was always the same as the initial context item (used for computing the values of global variables), and since this is the most common scenario, it is likely to affect the design of APIs.

  • Optionally, an initial mode.

    [Definition: The initial mode, if specified, must either be the default mode, or a mode that is explicitly named either in an xsl:mode declaration, or in the mode attribute of an xsl:template declaration within the stylesheet. If an initial mode is supplied, then in searching for the template rule that best matches the initial context item, the processor considers only those rules that apply to the initial mode. If no initial mode is supplied, then the mode used is that named in the default-mode attribute of the xsl:stylesheet element of the principal stylesheet module; or failing that, the mode named in the default-mode attribute of its containing xsl:package element; or in the absence of such an attribute, the unnamed mode.]

  • Parameters, which will be passed to the template rules used to process items in the input sequence. The parameters consist of two sets of (QName, value) pairs, one set for tunnel parameters and one for non-tunnel parameters, in which the QName identifies the name of a parameter and the value provides the value of the parameter. Either or both sets of parameters may be empty. The effect is the same as when a template is invoked using xsl:apply-templates with an xsl:with-param child specifying tunnel="yes" or tunnel="no" as appropriate. If a parameter is supplied that is not declared or used, the value is simply ignored. These parameters are not used to set stylesheet parameters.

    A supplied value is converted if necessary to the declared type of the template parameter using the function conversion rules.

The raw result of the invocation is the result of processing the supplied input sequence as if by a call on xsl:apply-templates in the specified mode: specifically, each item in the input sequence is processed by selecting and evaluating the best matching template rule, and converting the result (if necessary) to the type declared in the as attribute of that template using the function conversion rules; and the results of processing each item are then concatenated into a single sequence, respecting the order of items in the input sequence.

Note:

If the initial mode is a streamable mode, then streaming will only be possible if nodes in the input sequence are supplied in a form that allows such processing: for example, as a reference to a stream of parsing events.

Note:

The design of the API for invoking a transformation should provide some means for users to designate the unnamed mode as the initial mode in cases where it is not the default mode.

[ERR XTDE0044] It is a dynamic error if the invocation of the stylesheet specifies an initial mode and if no input sequence is supplied (either explicitly, or defaulted to the initial context item).

[ERR XTDE0045] It is a dynamic error if the invocation of the stylesheet specifies an initial mode (other than the unnamed mode) that does not match either the expanded QName in the name attribute of an xsl:mode declaration, or the expanded QName in the mode attribute of any template defined in the stylesheet.

Note:

A stylesheet can process further source documents in addition to those supplied when the transformation is invoked. These additional documents can be loaded using the functions document (see 20.1 fn:document) or docFO30 or collectionFO30 (see [Functions and Operators]), or using the xsl:stream instruction; alternatively, they can be supplied as stylesheet parameters (see 9.5 Global Variables and Parameters), or returned as the result of an extension function (see 23.1 Extension Functions).

2.3.4 Invoking an Initial Template

The following additional information is needed when dynamic evaluation is to start with a named template:

  • Optionally, the name of a named template which is to be executed as the entry point to the transformation. If no template name is supplied, the default template name is xsl:initial-template. The selected template must exist within the stylesheet.

  • Optionally, a context item for evaluation of this named template, defaulting to the initial context item if it exists.

  • Parameters, which will be passed to the selected template rule. The parameters consist of two sets of (QName, value) pairs, one set for tunnel parameters and one for non-tunnel parameters, in which the QName identifies the name of a parameter and the value provides the value of the parameter. Either or both sets of parameters may be empty. The effect is the same as when a template is invoked using xsl:call-template with an xsl:with-param child specifying tunnel="yes" or tunnel="no" as appropriate. If a parameter is supplied that is not declared or used, the value is simply ignored. These parameters are not used to set stylesheet parameters.

    A supplied value is converted if necessary to the declared type of the template parameter using the function conversion rules.

The raw result of the invocation is the result of evaluating the initial template, after conversion of the result to the type declared in the as attribute of that template using the function conversion rules, if such conversion is necessary.

[ERR XTDE0040] It is a dynamic error if the invocation of the stylesheet specifies a template name that does not match the expanded QName of a named template defined in the stylesheet, whose visibility is public or final.

[Definition: The transformation is performed by evaluating an initial template. If a named template is supplied when the transformation is initiated, then this is the initial template; otherwise, the initial template is the template rule selected according to the rules of the xsl:apply-templates instruction for processing the initial context item in the initial mode.]

It is a dynamic error [see ERR XTDE0060] if the initial template defines a template parameter that specifies required="yes" and no value is supplied for that parameter.

2.3.5 Invoking an Initial Function

The following additional information is needed when dynamic evaluation is to start with a stylesheet function

  • The name and arity of a stylesheet function which is to be executed as the entry point to the transformation.

    Note:

    In the design of a concrete API, the arity may be inferred from the length of the parameter list.

  • A list of values to act as parameters to the initial function. The number of values in the list must be the same as the arity of the function.

    A supplied value is converted if necessary to the declared type of the stylesheet parameter using the function conversion rules.

The raw result of the invocation is the result of evaluating the initial function, after conversion of the result to the type declared in the as attribute of that function using the function conversion rules, if such conversion is necessary.

[ERR XTDE0041] It is a dynamic error if the invocation of the stylesheet specifies a function name and arity that does not match the expanded QName and arity of a named stylesheet function defined in the stylesheet, whose visibility is public or final.

[Definition: The transformation is performed by evaluating an initial function. ]

[ERR XTDE0060] It is a dynamic error if the initial template defines a template parameter that specifies required="yes".

2.3.6 Post-processing the Raw Result

At user option, the raw result of a component invocation may either be returned to the calling application unchanged, or it may be post-processed. Two stages of post-processing are defined, both of which are optional:

  1. Result tree construction

    If the raw result is non-empty, then it is used to construct an implicit final result tree, following the rules described in 5.8.1 Constructing Complex Content: the effect is as if the raw result R were processed by the following function:

    <xsl:function name="construct-result-tree" as="document-node()">
      <xsl:param name="R" as="item()*">
      <xsl:document validation="preserve">
        <xsl:sequence select="$R"/>
      </xsl:document>  
    </xsl:function>
    

    An implicit result tree is also created when the raw result is empty, provided that no xsl:result-document instruction has been evaluated during the course of the transformation. In this situation the implicit result tree will consist of a document node with no children.

    Note:

    This means that there is always at least one result tree. It also means that if the content of the initial template is a single xsl:result-document instruction, as in the example above, then only one result tree is produced, not two. It is useful to make the result document explicit as this is a convenient way of invoking document-level validation. (Validation of the implicit result document can also be achieved by adding an xsl:document instruction to the initial template.)

    If the result of the initial template is non-empty, and an explicit xsl:result-document instruction has been evaluated with the empty attribute href="", then an error will occur [see ERR XTDE1490], since it is not possible to create two final result trees with the same URI.

  2. Serialization

    See 2.6 Parsing and Serialization.

    Either the raw result, or a result tree produced as described above, may optionally be serialized as decribed in [serialization].

    Note:

    The first phase of serialization, called sequence normalization, has no effect if the supplied value is a single document node, which will be the case if serialization is preceded by result tree construction. In the case of any other supplied value, the effect of sequence normalization is very similar to the effect of result tree construction, except where an item-separator serialization parameter is present. Use of item-separator allows, for example, a sequence of strings returned by invoking a stylesheet function to be output with newline separators.

Note:

This specification does not constrain the design of application programming interfaces or the choice of defaults. In previous versions of this specification, result tree construction was a mandatory process, while serialization was optional. When invoking stylesheet functions directly, however, result tree construction and serialization may be inappropriate as defaults. These considerations may affect the design of APIs.

2.4 Executing a Transformation

The classic method of executing an XSLT transformation is to apply template rules to an input document, delivering the result as a result tree which is then optionally serialized. This processing model is described in this section. Other ways of invoking a transformation or processing the result are outlined in the previous section.

[Definition: A stylesheet contains a set of template rules (see 6 Template Rules). A template rule has three parts: a pattern that is matched against nodes, a (possibly empty) set of template parameters, and a sequence constructor that is evaluated to produce a sequence of items.] In many cases these items are newly constructed nodes, which are then written to a result tree.

A transformation as a whole is executed by evaluating the sequence constructor of the initial template as described in 5.8 Sequence Constructors.

The result sequence produced by evaluating the initial template is handled as follows:

  1. If the initial template has an as attribute, then the result sequence of the initial template is checked against the required type in the same way as for any other template.

  2. If the result sequence is non-empty, then it is typically used to construct an implicit final result tree, following the rules described in 5.8.1 Constructing Complex Content: the effect is as if the initial template T were called by an implicit template of the form:

    <xsl:template name="IMPLICIT">
      <xsl:result-document href="">
        <xsl:call-template name="T"/>
      </xsl:result-document>
    </xsl:template>
    

The process of generating a result tree from the raw result of the initial template may be replaced with the very similar sequence normalization process described in 25 Serialization. In the latter case the serialization parameter item-separator may be used to separate items in the raw result with a string other than space (for example, newlines).

An implicit result tree is also created when the result sequence is empty, provided that no xsl:result-document instruction has been evaluated during the course of the transformation. In this situation the implicit result tree will consist of a document node with no children.

Note:

This means that there is always at least one result tree. It also means that if the content of the initial template is a single xsl:result-document instruction, as in the example above, then only one result tree is produced, not two. It is useful to make the result document explicit as this is the only way of invoking document-level validation.

If the result of the initial template is non-empty, and an explicit xsl:result-document instruction has been evaluated with the empty attribute href="", then an error will occur [see ERR XTDE1490], since it is not possible to create two final result trees with the same URI.

A sequence constructor is a sequence of sibling nodes in the stylesheet, each of which is either an XSLT instruction, a literal result element, a text node, or an extension instruction.

[Definition: An instruction is either an XSLT instruction or an extension instruction.]

[Definition: An XSLT instruction is an XSLT element whose syntax summary in this specification contains the annotation <!-- category: instruction -->.]

Extension instructions are described in 23.2 Extension Instructions.

The main categories of XSLT instruction are as follows:

Often, a sequence constructor will include an xsl:apply-templates instruction, which selects a sequence of nodes to be processed. Each of the selected nodes is processed by searching the stylesheet for a matching template rule and evaluating the sequence constructor of that template rule. The resulting sequences of items are concatenated, in order, to give the result of the xsl:apply-templates instruction, as described in 6.3 Applying Template Rules; this sequence is often added to a result tree. Since the sequence constructors of the selected template rules may themselves contain xsl:apply-templates instructions, this results in a cycle of selecting nodes, identifying template rules, constructing sequences, and constructing result trees, that recurses through a source tree.

2.5 The Evaluation Context

The results of some expressions and instructions in a stylesheet may depend on information provided contextually. This context information is divided into two categories: the static context, which is known during static analysis of the stylesheet, and the dynamic context, which is not known until the stylesheet is evaluated. Although information in the static context is known at analysis time, it is sometimes used during stylesheet evaluation.

Some context information can be set by means of declarations within the stylesheet itself. For example, the namespace bindings used for any XPath expression are determined by the namespace declarations present in containing elements in the stylesheet. Other information may be supplied externally or implicitly: an example is the current date and time.

The context information used in processing an XSLT stylesheet includes as a subset all the context information required when evaluating XPath expressions. The XPath 3.0 specification defines a static and dynamic context that the host language (in this case, XSLT) may initialize, which affects the results of XPath expressions used in that context. XSLT augments the context with additional information: this additional information is used firstly by XSLT constructs outside the scope of XPath (for example, the xsl:sort element), and secondly, by functions that are defined in the XSLT specification (such as key and current-group) that are available for use in XPath expressions appearing within a stylesheet.

The static context for an expression or other construct in a stylesheet is determined by the place in which it appears lexically. The details vary for different components of the static context, but in general, elements within a stylesheet module affect the static context for their descendant elements within the same stylesheet module.

The dynamic context is maintained as a stack. When an instruction or expression is evaluated, it may add dynamic context information to the stack; when evaluation is complete, the dynamic context reverts to its previous state. An expression that accesses information from the dynamic context always uses the value at the top of the stack.

The most commonly used component of the dynamic context is the context item. This is an implicit variable whose value is the item currently being processed (it may be a node, an atomic value, or a function item). The value of the context item can be referenced within an XPath expression using the expression . (dot).

Full details of the static and dynamic context are provided in 5.4 The Static and Dynamic Context.

2.6 Parsing and Serialization

An XSLT stylesheet describes a process that constructs a set of final result trees from a set of source trees.

The stylesheet does not describe how a source tree is constructed. Some possible ways of constructing source trees are described in [Data Model]. Frequently an implementation will operate in conjunction with an XML parser (or more strictly, in the terminology of [XML 1.0], an XML processor), to build a source tree from an input XML document. An implementation may also provide an application programming interface allowing the tree to be constructed directly, or allowing it to be supplied in the form of a DOM Document object (see [DOM Level 2]). This is outside the scope of this specification. Users should be aware, however, that since the input to the transformation is a tree conforming to the XDM data model as described in [Data Model], constructs that might exist in the original XML document, or in the DOM, but which are not within the scope of the data model, cannot be processed by the stylesheet and cannot be guaranteed to remain unchanged in the transformation output. Such constructs include CDATA section boundaries, the use of entity references, and the DOCTYPE declaration and internal DTD subset.

[Definition: A frequent requirement is to output a final result tree as an XML document (or in other formats such as HTML). This process is referred to as serialization.]

Like parsing, serialization is not part of the transformation process, and it is not required that an XSLT processor must be able to perform serialization. However, for pragmatic reasons, this specification describes declarations (the xsl:output element and the xsl:character-map declarations, see 25 Serialization), and attributes on the xsl:result-document instruction, that allow a stylesheet to specify the desired properties of a serialized output file. When serialization is not being performed, either because the implementation does not support the serialization option, or because the user is executing the transformation in a way that does not invoke serialization, then the content of the xsl:output and xsl:character-map declarations has no effect. Under these circumstances the processor may report any errors in an xsl:output or xsl:character-map declaration, or in the serialization attributes of xsl:result-document, but is not required to do so.

2.7 Packages and Modules

In previous versions of the XSLT language, it has been possible to structure a stylesheet as a collection of modules, using the xsl:include and xsl:import declarations to express the dependency of on module on others.

In XSLT 3.0 an additional layer of modularization of stylesheet code is enabled through the introduction of packages. A package is a collection of stylesheet modules with a controlled interface to the packages that use it: for example, it defines which functions and templates defined in the package are visible to callers, which are purely internal, and which are not only public but capable of being overridden by other functions and templates supplied by the using package.

Packages are introduced with several motivations, which broadly divide into two categories:

  1. Software engineering benefits: greater re-use of code, greater robustness through ease of testing, controlled evolution of code in response to new requirements, ability to deliver code that users cannot see or modify.

  2. Efficiency benefits: the ability to avoid compiling libraries repeatedly when they are used in multiple stylesheets, and to avoid holding multiple copies of the same library in memory simultaneously.

Packages are designed to allow separate compilation: that is, a package can be compiled independently of the packages that use it. This specification does not define a process model for compilation, or expand on what it means to compile different packages independently. Nor does it mandate that implementations offer any feature along these lines. It merely defines language features that are designed to make separate compilation of packages possible.

To achieve this, packages (unlike modules):

  • Must not contain unresolved references to functions, templates, or variables declared in other packages;

  • Have strict rules governing the ability to override declarations in a library package with declarations in a package that uses the library;

  • Constrain the visibility of component names and of context declarations such as the declarations of keys and decimal formats;

  • Can declare a mode (a collection of template rules) as final, which disallows the addition of new overriding template rules in a using package;

  • Require explicit disambiguation where naming conflicts arise, for example when a package uses two other packages that both export like-named components;

  • Allow multiple specializations of library components to coexist in the same application.

A package is defined by means of an XML document whose outermost element is an xsl:package element. This is referred to as the package manifest. The xsl:package element has child elements describing properties of the package, as well as an xsl:stylesheet or xsl:transform child element that defines the content of the package, either directly or by reference through one or more xsl:import or xsl:include declarations.

When no packages are explicitly defined, the entire stylesheet is treated as a single package; the effect is as if the principal stylesheet module were wrapped in an xsl:package element with no other information in the package manifest.

2.8 Extensibility

XSLT defines a number of features that allow the language to be extended by implementers, or, if implementers choose to provide the capability, by users. These features have been designed, so far as possible, so that they can be used without sacrificing interoperability. Extensions other than those explicitly defined in this specification are not permitted.

These features are all based on XML namespaces; namespaces are used to ensure that the extensions provided by one implementer do not clash with those of a different implementer.

The most common way of extending the language is by providing additional functions, which can be invoked from XPath expressions. These are known as extension functions, and are described in 23.1 Extension Functions.

It is also permissible to extend the language by providing new instructions. These are referred to as extension instructions, and are described in 23.2 Extension Instructions. A stylesheet that uses extension instructions in a particular namespace must declare that it is doing so by using the [xsl:]extension-element-prefixes attribute.

Extension instructions and extension functions defined according to these rules may be provided by the implementer of the XSLT processor, and the implementer may also provide facilities to allow users to create further extension instructions and extension functions.

This specification defines how extension instructions and extension functions are invoked, but the facilities for creating new extension instructions and extension functions are implementation-defined. For further details, see 23 Extensibility and Fallback.

The XSLT language can also be extended by the use of extension attributes (see 3.3 Extension Attributes), and by means of user-defined data elements (see 3.8.3 User-defined Data Elements).

2.9 Stylesheets and XML Schemas

An XSLT stylesheet can make use of information from a schema. An XSLT transformation can take place in the absence of a schema (and, indeed, in the absence of a DTD), but where the source document has undergone schema validity assessment, the XSLT processor has access to the type information associated with individual nodes, not merely to the untyped text.

Information from a schema can be used both statically (when the stylesheet is compiled), and dynamically (during evaluation of the stylesheet to transform a source document).

There are places within a stylesheet, and within XPath expressions and patterns in a stylesheet, where it is possible to refer to named type definitions in a schema, or to element and attribute declarations. For example, it is possible to declare the types expected for the parameters of a function. This is done using the SequenceTypeXP30 syntax defined in [XPath 3.0].

[Definition: Type definitions and element and attribute declarations are referred to collectively as schema components.]

[Definition: The schema components that may be referenced by name in a stylesheet are referred to as the in-scope schema components. This set is the same throughout all the modules of a stylesheet.]

The conformance rules for XSLT 3.0, defined in 26 Conformance, distinguish between a basic XSLT processor and a schema-aware XSLT processor. As the names suggest, a basic XSLT processor does not support the features of XSLT that require access to schema information, either statically or dynamically. A stylesheet that works with a basic XSLT processor will produce the same results with a schema-aware XSLT processor provided that the source documents are untyped (that is, they are not validated against a schema). However, if source documents are validated against a schema then the results may be different from the case where they are not validated. Some constructs that work on untyped data may fail with typed data (for example, an attribute of type xs:date cannot be used as an argument of the substringFO30 function) and other constructs may produce different results depending on the datatype (for example, given the element <product price="10.00" discount="2.00"/>, the expression @price gt @discount will return true if the attributes have type xs:decimal, but will return false if they are untyped).

There is a standard set of type definitions that are always available as in-scope schema components in every stylesheet. These are defined in 3.15 Built-in Types.

The remainder of this section describes facilities that are available only with a schema-aware XSLT processor.

Additional schema components (type definitions, element declarations, and attribute declarations) may be added to the in-scope schema components by means of the xsl:import-schema declaration in a stylesheet.

The xsl:import-schema declaration may reference an external schema document by means of a URI, or it may contain an inline xs:schema element.

It is only necessary to import a schema explicitly if one or more of its schema components are referenced explicitly by name in the stylesheet; it is not necessary to import a schema merely because the stylesheet is used to process a source document that has been assessed against that schema. It is possible to make use of the information resulting from schema assessment (for example, the fact that a particular attribute holds a date) even if no schema has been imported by the stylesheet.

Importing a schema does not of itself say anything about the type of the source document that the stylesheet is expected to process. The imported type definitions can be used for temporary nodes or for nodes on a result tree just as much as for nodes in source documents. It is possible to make assertions about the type of an input document by means of tests within the stylesheet. For example:

Example: Asserting the Required Type of the Source Document
<xsl:mode initial="yes" typed="lax">
  <xsl:context-item use="required"
                    as="document-node(schema-element(my:invoice))"/>
</xsl:mode>

This example will cause the transformation to fail with an error message when the initial mode is the unnamed mode, unless the document element of the source document is valid against the top-level element declaration my:invoice, and has been annotated as such.

The setting typed="lax" further ensures that in any match pattern for a template rule in this mode, an element name that corresponds to the name of an element declaration in the schema is taken as referring to elements validated against that declaration: for example, match="employee" will only match a validated employee element. Selecting this option enables the XSLT processor to do more compile-time type-checking against the schema, for example it allows the processor to produce warning or error messages when path expressions contain misspelt element names, or confuse an element with an attribute.

It is also true that importing a schema does not of itself say anything about the structure of the result tree. It is possible to request validation of a result tree against the schema by using the xsl:result-document instruction, for example:

Example: Requesting Validation of the Result Document
<xsl:template match="/">
  <xsl:result-document validation="strict">
    <xhtml:html>
      <xsl:apply-templates/>
    </xhtml:html>
  </xsl:result-document>
</xsl:template>
               

This example will cause the transformation to fail with an error message unless the document element of the result document is valid against the top-level element declaration xhtml:html.

It is possible that a source document may contain nodes whose type annotation is not one of the types imported by the stylesheet. This creates a potential problem because in the case of an expression such as data(.) instance of xs:integer the system needs to know whether the type named in the type annotation of the context node is derived by restriction from the type xs:integer. This information is not explicitly available in an XDM tree, as defined in [Data Model]. The implementation may choose one of several strategies for dealing with this situation:

  1. The processor may signal a dynamic error if a source document is found to contain a type annotation that is not known to the processor.

  2. The processor may maintain additional metadata, beyond that described in [Data Model], that allows the source document to be processed as if all the necessary schema information had been imported using xsl:import-schema. Such metadata might be held in the data structure representing the source document itself, or it might be held in a system catalog or repository.

  3. The processor may be configured to use a fixed set of schemas, which are automatically used to validate all source documents before they can be supplied as input to a transformation. In this case it is impossible for a source document to have a type annotation that the processor is not aware of.

  4. The processor may be configured to treat the source document as if no schema processing had been performed, that is, effectively to strip all type annotations from elements and attributes on input, marking them instead as having type xs:untyped and xs:untypedAtomic respectively.

Where a stylesheet author chooses to make assertions about the types of nodes or of variables and parameters, it is possible for an XSLT processor to perform static analysis of the stylesheet (that is, analysis in the absence of any source document). Such analysis may reveal errors that would otherwise not be discovered until the transformation is actually executed. An XSLT processor is not required to perform such static type-checking. Under some circumstances (see 2.11 Error Handling) type errors that are detected early may be reported as static errors. In addition an implementation may report any condition found during static analysis as a warning, provided that this does not prevent the stylesheet being evaluated as described by this specification.

A stylesheet can also control the type annotations of nodes that it constructs in a final result tree, or in temporary trees. This can be done in a number of ways.

  • It is possible to request explicit validation of a complete document, that is, a tree rooted at a document node. This applies both to temporary trees constructed using the xsl:document (or xsl:copy) instruction and also to final result trees constructed using xsl:result-document. Validation is either strict or lax, as described in [XML Schema Part 1]. If validation of a result tree fails (strictly speaking, if the outcome of the validity assessment is invalid), then the transformation fails, but in all other cases, the element and attribute nodes of the tree will be annotated with the names of the types to which these nodes conform. These type annotations will be discarded if the result tree is serialized as an XML document, but they remain available when the result tree is passed to an application (perhaps another stylesheet) for further processing.

  • It is also possible to validate individual element and attribute nodes as they are constructed. This is done using the type and validation attributes of the xsl:element, xsl:attribute, xsl:copy, and xsl:copy-of instructions, or the xsl:type and xsl:validation attributes of a literal result element.

  • When elements, attributes, or document nodes are copied, either explicitly using the xsl:copy or xsl:copy-of instructions, or implicitly when nodes in a sequence are attached to a new parent node, the options validation="strip" and validation="preserve" are available, to control whether existing type annotations are to be retained or not.

When nodes in a temporary tree are validated, type information is available for use by operations carried out on the temporary tree, in the same way as for a source document that has undergone schema assessment.

For details of how validation of element and attribute nodes works, see 24.2 Validation.

2.10 Streaming

[Definition: The term streaming refers to a manner of processing in which documents (such as source and result documents) are not represented by a complete tree of nodes occupying memory proportional to document size, but instead are processed "on the fly" as a sequence of events, similar in concept to the stream of events notified by an XML parser to represent markup in lexical XML.]

[Definition: A streamed document is a source tree that is processed using streaming, that is, without constructing a complete tree of nodes in memory.]

[Definition: A streamed node is a node in a streamed document.]

Many processors implementing earlier versions of this specification have adopted an architecture that allows streaming of the result tree directly to a serializer, without first materializing the complete result tree in memory. Streaming of the source tree, however, has proved to be more difficult without subsetting the language. This has created a situation where documents exceeding the capacity of virtual memory could not be transformed. XSLT 3.0 therefore introduces facilities allowing stylesheets to be written in a way that makes streaming of source documents possible, without excessive reliance on processor-specific optimization techniques.

Streaming achieves two important objectives: it allows large documents to be transformed without requiring correspondingly large amounts of memory; and it allows the processor to start producing output before it has finished receiving its input, thus reducing latency.

This specification does not attempt to legislate precisely which implementation techniques fall under the definition of streaming, and which do not. A number of techniques are available that reduce memory requirements, while still requiring a degree of buffering, or allocation of memory to partial results. A stylesheet that requests streaming of a source document is indicating that the processor should avoid assuming that the entire source document will fit in memory; in return, the stylesheet must be written in a way that makes streaming possible. This specification does not attempt to describe the algorithms that the processor should actually use, or to impose quantitative constraints on the resources that these algorithms should consume.

Nothing in this specification, nor in its predecessors [XSLT 1.0] and [XSLT 2.0], prevents a processor using streaming whenever it sees an opportunity to do so. However, experience has shown that in order to achieve streaming, it is often necessary to write stylesheet code in such a way as to make this possible. Therefore, XSLT 3.0 provides explicit constructs allowing the stylesheet author to request streaming, and defines explicit static constraints on the structure of the code which are designed to make streaming possible.

A processor that claims conformance with the streaming option offers a guarantee that when streaming is requested for a source document, and when the stylesheet conforms to the rules that make the processing guaranteed-streamable, then an algorithm will be adopted in which memory consumption is either completely independent of document size, or increases only very slowly as document size increases, allowing documents to be processed that are orders-of-magnitude larger than the physical memory available. A processor that does not claim conformance with the streaming option must still process a stylesheet and deliver the correct results, but is not required to use streaming algorithms, and may therefore fail with out-of-memory errors when presented with large source documents.

Apart from the fact that there are constructs to request streaming, and rules that must be followed to guarantee that streaming is possible, the language has been designed so there are as few differences as possible between streaming and non-streaming evaluation. The semantics of the language continue to be expressed in terms of the XDM data model, which is substantively unchanged; but readers must take care to observe that when terms like "node" and "axis" are used, the concepts are completely abstract and may have no direct representation in the run-time execution environment.

Streamed processing of a document can be initiated in one of two ways:

  • The initial mode can be declared as a streamable mode. In this case the initial context item will generally be a document node, and it will be supplied by the calling application in a form that allows streaming (that is, in some form other than a tree in memory; for example, as a reference to a push or pull XML parser primed to deliver a stream of events). The type of the initial context item can be constrained using the xsl:context-item element.

  • Streamed processing of any document can be initiated using the xsl:stream instruction. This has an attribute href whose value is the URI of a document to be processed using streaming, and the actual processing to be applied is defined by the instructions written as children of the xsl:stream instruction.

The rules for streamability, which are defined in detail in 19 Streamability, impose two main constraints:

  • The only nodes reachable from the node that is currently being processed are its attributes and namespaces, its ancestors and their attributes and namespaces, and its descendants and their attributes and namespaces. The siblings of the node, and the siblings of its ancestors, are not reachable in the tree, and any attempt to use their values is a static error. However, constructs (for example, simple forms of xsl:number, and simple positional patterns) that require knowledge of the number of preceding elements by name are permitted.

  • When processing a given node in the tree, each descendant node can only be visited once. Essentially this allows two styles of processing: either visit each of the children once, and then process that child with the same restrictions applied; or process all the descendants in a single pass, in which case it is not possible while processing a descendant to make any further downward selection.

The second restriction, that only one visit to the children is allowed, means that XSLT code that was not designed with streaming in mind will often need to be rewritten to make it streamable. In many cases it is possible to do this using a technique sometimes called windowing or burst-mode streaming (note this is not quite the same meaning as windowing in XQuery 3.0). Many XML documents consist of a large number of elements, each of manageable size, representing transactions or business objects where each such element can be processed independently: in such cases, an effective design pattern is to write a streaming transformation that takes a snapshot of each element in turn, processing the snapshot using the full power of the XSLT language. Each snapshot is a tree built in memory and is therefore fully navigable. For details see the snapshot and copy-of functions.

The new facility of accumulators allows applications complete control over how much information is retained (and by implication, how much memory is required) in the course of a pass over a streamed document. An accumulator computes a value for every node in a streamed document: or more accurately, two values, one for the first visit to a node (before visiting its descendants), and a second value for the second visit to the node (after visiting the descendants). The computation is structured in such a way that the value for a given node can depend only on the value for the previous node in document order together with the data available when positioned at the current node (for example, the attribute values). Based on the well-established fold operation of functional programming languages, accumulators provide the convenience and economy of mutable variables while remaining within the constraints of a purely declarative processing model.

Streaming applications often fall into one of the following categories:

  • Aggregation applications, where a single aggregation operation (perhaps countFO30, sumFO30, existsFO30, or distinct-valuesFO30) is applied to a set of elements selected from the streamed source document by means of a path expression.

  • Record-at-a-time applications, where the source document consists of a long sequence of elements with similar structure ("records"), and each "record" is processed using the same logic, independently of any other "records". This kind of processing is facilitated using the snapshot and copy-of function mentioned earlier.

  • Grouping applications, where the output follows the structure of the input, except that an extra layer of hierarchy is added. For example, the input might be a flat series of banking transactions in date/time order, and the output might contain the same transactions grouped by date.

  • Accumulator applications, which are the same as record-at-a-time applications, except that the processing of one "record" might depend on data encountered earlier in the document. A classical example is processing a sequence of banking transactions in which the input transaction contains a debit or credit amount, and the output adds a running total (the account balance). The xsl:iterate instruction has been introduced to facilitate this style of processing.

  • Isomorphic transformations, in which there is an ordered (often largely one-to-one) relationship between the nodes of the source tree and the nodes of the result tree: for example, transformations that involve only the renaming or selective deletion of nodes, or scalar manipulations of the values held in the leaf nodes. Such transformations are most conveniently expressed using recursive application of template rules. This is possible with a streamed input document only if all the template rules adhere to the constraints required for streamability. To enforce these rules, while still allowing unrestricted processing of other documents within the same transformation, all streaming evaluation must be carried out using a specific mode, which is declared to be a streaming mode by means of an xsl:mode declaration in the stylesheet.

There are important classes of application in which streaming is possible only if multiple streams can be processed in parallel. This specification therefore provides facilities:

  1. allowing multiple sorted input sequences to be merged into one sorted output sequence (the xsl:merge instruction)

  2. allowing multiple output sequences to be generated during a single pass of an input sequence (the xsl:fork instruction).

These facilities have been designed in such a way that they can readily be implemented using streaming, that is, without materializing the input or output sequences in memory.

2.11 Error Handling

[Definition: An error that can be detected by examining a stylesheet before execution starts (that is, before the source document and values of stylesheet parameters are available) is referred to as a static error.]

Errors classified in this specification as static errors must be signaled by all implementations: that is, the processor must indicate that the error is present. A static error must be signaled even if it occurs in a part of the stylesheet that is never evaluated. Static errors are never recoverable. After signaling a static error, a processor may continue for the purpose of signaling additional errors, but it must eventually terminate abnormally without producing any final result tree.

There is an exception to this rule when the stylesheet specifies forwards compatible behavior (see 3.11 Forwards Compatible Processing).

Generally, errors in the structure of the stylesheet, or in the syntax of XPath expressions contained in the stylesheet, are classified as static errors. Where this specification states that an element in the stylesheet must or must not appear in a certain position, or that it must or must not have a particular attribute, or that an attribute must or must not have a value satisfying specified conditions, then any contravention of this rule is a static error unless otherwise specified.

[Definition: An error that is not detected until a source document is being transformed is referred to as a dynamic error.]

When a dynamic error occurs, and is not caught using xsl:catch, the processor must signal the error, and the transformation fails.

Because different implementations may optimize execution of the stylesheet in different ways, the detection of dynamic errors is to some degree implementation-dependent. In cases where an implementation is able to produce the final result trees without evaluating a particular construct, the implementation is never required to evaluate that construct solely in order to determine whether doing so causes a dynamic error. For example, if a variable is declared but never referenced, an implementation may choose whether or not to evaluate the variable declaration, which means that if evaluating the variable declaration causes a dynamic error, some implementations will signal this error and others will not.

There are some cases where this specification requires that a construct must not be evaluated: for example, the content of an xsl:if instruction must not be evaluated if the test condition is false. This means that an implementation must not signal any dynamic errors that would arise if the construct were evaluated.

An implementation may signal a dynamic error before any source document is available, but only if it can determine that the error would be signaled for every possible source document and every possible set of parameter values. For example, some circularity errors fall into this category: see 9.11 Circular Definitions.

There are also some dynamic errors where the specification gives a processor license to signal the error during the analysis phase even if the construct might never be executed; an example is the use of an invalid QName as a literal argument to a function such as key, or the use of an invalid regular expression in the regex attribute of the xsl:analyze-string instruction.

A dynamic error may also be signaled during the static analysis phase if the error occurs during evaluation of a static expression.

The XPath specification states (see Section 2.3.1 Kinds of Errors XP30) that if any expression (at any level) can be evaluated during the analysis phase (because all its explicit operands are known and it has no dependencies on the dynamic context), then any error in performing this evaluation may be reported as a static error. For XPath expressions used in an XSLT stylesheet, however, any such errors must not be reported as static errors in the stylesheet unless they would occur in every possible evaluation of that stylesheet; instead, they must be signaled as dynamic errors, and signaled only if the XPath expression is actually evaluated.

Example: Errors in Constant Subexpressions

An XPath processor may report statically that the expression 1 div 0 fails with a "divide by zero" error. But suppose this XPath expression occurs in an XSLT construct such as:

<xsl:choose>
  <xsl:when test="system-property('xsl:version') = '1.0'">
    <xsl:value-of select="1 div 0"/>
  </xsl:when>
  <xsl:otherwise>
    <xsl:value-of select="xs:double('INF')"/>
  </xsl:otherwise>
</xsl:choose>

Then the XSLT processor must not report an error, because the relevant XPath construct appears in a context where it will never be executed by an XSLT 2.0 or 3.0 processor. (An XSLT 1.0 processor will execute this code successfully, returning positive infinity, because it uses double arithmetic rather than decimal arithmetic.)

[Definition: Certain errors are classified as type errors. A type error occurs when the value supplied as input to an operation is of the wrong type for that operation, for example when an integer is supplied to an operation that expects a node.] If a type error occurs in an instruction that is actually evaluated, then it must be signaled in the same way as a dynamic error. Alternatively, an implementation may signal a type error during the analysis phase in the same way as a static error, even if it occurs in part of the stylesheet that is never evaluated, provided it can establish that execution of a particular construct would never succeed.

It is implementation-defined whether type errors are signaled statically.

Example: A Type Error

The following construct contains a type error, because 42 is not allowed as the value of the select expression of the xsl:number instruction (it must be a node). An implementation may optionally signal this as a static error, even though the offending instruction will never be evaluated, and the type error would therefore never be signaled as a dynamic error.

<xsl:if test="false()">
  <xsl:number select="42"/>
</xsl:if>

On the other hand, in the following example it is not possible to determine statically whether the operand of xsl:number will have a suitable dynamic type. An implementation may produce a warning in such cases, but it must not treat it as an error.

<xsl:template match="para">
  <xsl:param name="p" as="item()"/>
  <xsl:number select="$p"/>
</xsl:template>

If more than one error arises, an implementation is not required to signal any errors other than the first one that it detects. It is implementation-dependent which of the several errors is signaled. This applies both to static errors and to dynamic errors. An implementation is allowed to signal more than one error, but if any errors have been signaled, it must not finish as if the transformation were successful.

When a transformation signals one or more dynamic errors, the final state of any persistent resources updated by the transformation is implementation-dependent. Implementations are not required to restore such resources to their initial state. In particular, where a transformation produces multiple result documents, it is possible that one or more serialized result documents may be written successfully before the transformation terminates, but the application cannot rely on this behavior.

Everything said above about error handling applies equally to errors in evaluating XSLT instructions, and errors in evaluating XPath expressions. Static errors and dynamic errors may occur in both cases.

[Definition: If a transformation has successfully produced a final result tree, it is still possible that errors may occur in serializing the result tree. For example, it may be impossible to serialize the result tree using the encoding selected by the user. Such an error is referred to as a serialization error.] If the processor performs serialization, then it must do so as specified in 25 Serialization, and in particular it must signal any serialization errors that occur.

Errors are identified by a QName. For errors defined in this specification, the namespace of the QName is always http://www.w3.org/2005/xqt-errors (and is therefore not given explicitly), while the local part is an 8-character code in the form PPSSNNNN. Here PP is always XT (meaning XSLT), and SS is one of SE (static error), DE (dynamic error), RE (recoverable dynamic error), or TE (type error). Note that the allocation of an error to one of these categories is purely for convenience and carries no normative implications about the way the error is handled. Many errors, for example, can be reported either dynamically or statically. These error codes are used to label error conditions in this specification, and are summarized in E Summary of Error Conditions.

Errors defined in related specifications ([XPath 3.0], [Functions and Operators] [XSLT and XQuery Serialization]) use QNames with a similar structure, in the same namespace. When errors occur in processing XPath expressions, an XSLT processor should use the original error code reported by the XPath processor, unless a more specific XSLT error code is available.

Implementations must use the codes defined in these specifications when signaling errors, to ensure that xsl:catch behaves in an interoperable way across implementations. Stylesheet authors should note, however, that there are many examples of errors where more than one rule in this specification is violated, and where the processor therefore has discretion in deciding which error code to associate with the condition: there is therefore no guarantee that different processors will always use the same error code for the same erroneous input.

Additional errors defined by an implementation (or by an application) may use QNames in an implementation-defined (or user-defined) namespace without risk of collision.

3 Stylesheet Structure

This section describes the overall structure of a stylesheet as a collection of XML documents.

3.1 XSLT Namespace

[Definition: The XSLT namespace has the URI http://www.w3.org/1999/XSL/Transform. It is used to identify elements, attributes, and other names that have a special meaning defined in this specification.]

Note:

The 1999 in the URI indicates the year in which the URI was allocated by the W3C. It does not indicate the version of XSLT being used, which is specified by attributes (see 3.8 Stylesheet Element and 3.9 Simplified Stylesheet Modules).

XSLT processors must use the XML namespaces mechanism [Namespaces in XML] to recognize elements and attributes from this namespace. Elements from the XSLT namespace are recognized only in the stylesheet and not in the source document. The complete list of XSLT-defined elements is specified in D Element Syntax Summary. Implementations must not extend the XSLT namespace with additional elements or attributes. Instead, any extension must be in a separate namespace. Any namespace that is used for additional instruction elements must be identified by means of the extension instruction mechanism specified in 23.2 Extension Instructions.

This specification uses a prefix of xsl: for referring to elements in the XSLT namespace. However, XSLT stylesheets are free to use any prefix, provided that there is a namespace declaration that binds the prefix to the URI of the XSLT namespace.

Note:

Throughout this specification, an element or attribute that is in no namespace, or an expanded QName whose namespace part is an empty sequence, is referred to as having a null namespace URI.

Note:

The conventions used for the names of XSLT elements, attributes and functions are that names are all lower-case, use hyphens to separate words, and use abbreviations only if they already appear in the syntax of a related language such as XML or HTML. Names of types defined in XML Schema are regarded as single words and are capitalized exactly as in XML Schema. This sometimes leads to composite function names such as current-dateTimeFO30.

3.2 Reserved Namespaces

[Definition: The XSLT namespace, together with certain other namespaces recognized by an XSLT processor, are classified as reserved namespaces and must be used only as specified in this and related specifications.] The reserved namespaces are those listed below.

  • The XSLT namespace, described in 3.1 XSLT Namespace, is reserved.

  • [Definition: The standard function namespace http://www.w3.org/2005/xpath-functions is used for functions in the function library defined in [Functions and Operators] and for standard functions defined in this specification.]

  • The namespace http://www.w3.org/2005/xpath-functions/math is used for mathematical functions in the function library defined in [Functions and Operators].

  • The namespace http://www.w3.org/2005/xpath-functions/map is used for functions defined in this specification relating to the manipulation of maps.

  • [Definition: The XML namespace, defined in [Namespaces in XML] as http://www.w3.org/XML/1998/namespace, is used for attributes such as xml:lang, xml:space, and xml:id.]

  • [Definition: The schema namespace http://www.w3.org/2001/XMLSchema is used as defined in [XML Schema Part 1]]. In a stylesheet this namespace may be used to refer to built-in schema datatypes and to the constructor functions associated with those datatypes.

  • [Definition: The schema instance namespace http://www.w3.org/2001/XMLSchema-instance is used as defined in [XML Schema Part 1]]. Attributes in this namespace, if they appear in a stylesheet, are treated by the XSLT processor in the same way as any other attributes.

  • [Definition: The standard error namespace http://www.w3.org/2005/xqt-errors is used for error codes defined in this specification and related specifications. It is also used for the names of certain predefined variables accessible within the scope of an xsl:catch element.]

  • The namespace http://www.w3.org/2000/xmlns/ is reserved for use as described in [Namespaces in XML]. No element or attribute node can have a name in this namespace, and although the prefix xmlns is implicitly bound to this namespace, no namespace node will ever define this binding.

Reserved namespaces may be used without restriction to refer to the names of elements and attributes in source documents and result documents. As far as the XSLT processor is concerned, reserved namespaces other than the XSLT namespace may be used without restriction in the names of literal result elements and user-defined data elements, and in the names of attributes of literal result elements or of XSLT elements: but other processors may impose restrictions or attach special meaning to them. Reserved namespaces must not be used, however, in the names of stylesheet-defined objects such as variables and stylesheet functions.

Note:

With the exception of the XML namespace, any of the above namespaces that are used in a stylesheet must be explicitly declared with a namespace declaration. Although conventional prefixes are used for these namespaces in this specification, any prefix may be used in a user stylesheet.

[ERR XTSE0080] It is a static error to use a reserved namespace in the name of a named template, a mode, an attribute set, a key, a decimal-format, a variable or parameter, a stylesheet function, a named output definition, or a character map.

3.3 Extension Attributes

[Definition: An element from the XSLT namespace may have any attribute not from the XSLT namespace, provided that the expanded QName (see [XPath 3.0]) of the attribute has a non-null namespace URI. These attributes are referred to as extension attributes.] The presence of an extension attribute must not cause the final result trees produced by the transformation to be different from the result trees that a conformant XSLT 3.0 processor might produce. They must not cause the processor to fail to signal an error that a conformant processor is required to signal. This means that an extension attribute must not change the effect of any instruction except to the extent that the effect is implementation-defined or implementation-dependent.

Furthermore, if serialization is performed using one of the serialization methods xml, xhtml, html, or text described in [XSLT and XQuery Serialization], the presence of an extension attribute must not cause the serializer to behave in a way that is inconsistent with the mandatory provisions of that specification.

Note:

Extension attributes may be used to modify the behavior of extension functions and extension instructions. They may be used to select processing options in cases where the specification leaves the behavior implementation-defined or implementation-dependent. They may also be used for optimization hints, for diagnostics, or for documentation.

Extension attributes may also be used to influence the behavior of the serialization methods xml, xhtml, html, or text, to the extent that the behavior of the serialization method is implementation-defined or implementation-dependent. For example, an extension attribute might be used to define the amount of indentation to be used when indent="yes" is specified. If a serialization method other than one of these four is requested (using a prefixed QName in the method parameter) then extension attributes may influence its behavior in arbitrary ways. Extension attributes must not be used to cause the four standard serialization methods to behave in a non-conformant way, for example by failing to report serialization errors that a serializer is required to report. An implementation that wishes to provide such options must create a new serialization method for the purpose.

An implementation that does not recognize the name of an extension attribute, or that does not recognize its value, must perform the transformation as if the extension attribute were not present. As always, it is permissible to produce warning messages.

The namespace used for an extension attribute will be copied to the result tree in the normal way if it is in scope for a literal result element. This can be prevented using the [xsl:]exclude-result-prefixes attribute.

Example: An Extension Attribute for xsl:message

The following code might be used to indicate to a particular implementation that the xsl:message instruction is to ask the user for confirmation before continuing with the transformation:

<xsl:message abc:pause="yes"
    xmlns:abc="http://vendor.example.com/xslt/extensions">
       Phase 1 complete
</xsl:message>

Implementations that do not recognize the namespace http://vendor.example.com/xslt/extensions will simply ignore the extra attribute, and evaluate the xsl:message instruction in the normal way.

[ERR XTSE0090] It is a static error for an element from the XSLT namespace to have an attribute whose namespace is either null (that is, an attribute with an unprefixed name) or the XSLT namespace, other than attributes defined for the element in this document.

3.4 XSLT Media Type

The media type application/xslt+xml has been registered for XSLT stylesheet modules.

The definition of the media type is at [XSLT Media Type].

This media type should be used for an XML document containing a standard stylesheet module at its top level, and it may also be used for a simplified stylesheet module. It should not be used for an XML document containing an embedded stylesheet module.

3.5 Standard Attributes

[Definition: There are a number of standard attributes that may appear on any XSLT element: specifically default-collation, default-mode, default-validation, exclude-result-prefixes, expand-text, extension-element-prefixes, use-when, version, and xpath-default-namespace.]

These attributes may also appear on a literal result element, but in this case, to distinguish them from user-defined attributes, the names of the attributes are in the XSLT namespace. They are thus typically written as xsl:default-collation, xsl:default-mode, xsl:default-validation, xsl:exclude-result-prefixes, xsl:expand-text, xsl:extension-element-prefixes, xsl:use-when, xsl:version, or xsl:xpath-default-namespace.

It is recommended that all these attributes should also be permitted on extension instructions, but this is at the discretion of the implementer of each extension instruction. They may also be permitted on user-defined data elements, though they will only have any useful effect in the case of data elements that are designed to behave like XSLT declarations or instructions.

In the following descriptions, these attributes are referred to generically as [xsl:]version, and so on.

These attributes all affect the element they appear on, together with any elements and attributes that have that element as an ancestor. The two forms with and without the XSLT namespace have the same effect; the XSLT namespace is used for the attribute if and only if its parent element is not in the XSLT namespace.

In the case of [xsl:]default-collation, [xsl:]expand-text, [xsl:]version, and [xsl:]xpath-default-namespace, the value can be overridden by a different value for the same attribute appearing on a descendant element. The effective value of the attribute for a particular stylesheet element is determined by the innermost ancestor-or-self element on which the attribute appears.

In an embedded stylesheet module, standard attributes appearing on ancestors of the outermost element of the stylesheet module have no effect.

In the case of [xsl:]exclude-result-prefixes and [xsl:]extension-element-prefixes the values are cumulative. For these attributes, the value is given as a whitespace-separated list of namespace prefixes, and the effective value for an element is the combined set of namespace URIs designated by the prefixes that appear in this attribute for that element and any of its ancestor elements. Again, the two forms with and without the XSLT namespace are equivalent.

The effect of the [xsl:]use-when attribute is described in 3.14 Conditional Element Inclusion.

Because these attributes may appear on any XSLT element, they are not listed in the syntax summary of each individual element. Instead they are listed and described in the entry for the xsl:stylesheet, xsl:transform, and xsl:package elements only. This reflects the fact that these attributes are often used on the outermost element of the stylesheet, in which case they apply to the entire stylesheet module or package manifest.

Note that the effect of these attributes does not extend to stylesheet modules referenced by xsl:include or xsl:import declarations, nor to packages referenced using xsl:use-package.

For the detailed effect of each attribute, see the following sections:

[xsl:]default-collation

see 3.8.1 The default-collation Attribute

[xsl:]default-mode

see 3.8.2 The [xsl:]default-mode Attribute

[xsl:]default-validaion

see 24.2 Validation

[xsl:]exclude-result-prefixes

see 11.1.3 Namespace Nodes for Literal Result Elements

[xsl:]expand-text

see 5.7.2 Text Value Templates

[xsl:]extension-element-prefixes

see 23.2 Extension Instructions

[xsl:]use-when

see 3.14 Conditional Element Inclusion

[xsl:]version

see 3.10 Backwards Compatible Processing and 3.11 Forwards Compatible Processing

[xsl:]xpath-default-namespace

see 5.2 Unprefixed Lexical QNames in Expressions and Patterns

3.6 Packages

[Definition: A package is represented by an xsl:package element, which will generally be the outermost element of an XML document.] (This specification does not preclude the xsl:package being embedded in another XML document, but it will never have any other XSLT element as an ancestor).

<xsl:package
  name? = uri
  package-version? = string
  version = decimal
  input-type-annotations? = "preserve" | "strip" | "unspecified"
  default-mode? = eqname | "#unnamed"
  default-validation? = "preserve" | "strip"
  default-collation? = uris
  extension-element-prefixes? = prefixes
  exclude-result-prefixes? = prefixes
  expand-text? = "yes" | "no"
  use-when? = expression
  xpath-default-namespace? = uri >
  <!-- Content: (xsl:use-package*, (xsl:stylesheet | xsl:transform), xsl:expose*) -->
</xsl:package>

[Definition: The content of the xsl:package element is referred to as the package manifest].

The version attribute indicates the version of the XSLT language specification to which the package manifest conforms. The value should be 3.0.

A package typically has a name, given in its name attribute, which must be an absolute URI. Unnamed packages are allowed, but they can only be used as the "top level" of an application; they cannot be the target of a xsl:use-package declaration in another package.

A package may have a version identifier, given in its package-version attribute. This is used to distinguish different packages that have the same package name, perhaps successive versions of a package, or perhaps variants of a package for use in different environments. The version identifier can be any string.

The attributes default-collation, default-mode, default-validation, exclude-result-prefixes, expand-text, extension-element-prefixes, use-when, version, and xpath-default-namespace are standard attributes that can appear on any XSLT element, and potentially affect all descendant elements. Their meaning is described in 3.5 Standard Attributes.

The package manifest is in three parts:

  1. It starts with zero-or-more xsl:use-package elements which identify the packages used by this package, including subsidiary elements that constrain the way in which the components contained in those packages are used.

  2. This is followed by an xsl:stylesheet or xsl:transform element (the two names are synonyms) which is an embedded standard stylesheet module. This can contain references to other stylesheet modules using xsl:include and/or xsl:import declarations, and it can contain other declarations such as xsl:function and xsl:template.

    The modules making up a package are this module, plus all modules that are transitively reachable from it using xsl:import and xsl:include declarations. It is permissible for the same module to appear in more than one package, or indeed more than once in the same package; this situation is no different from having two modules with identical content but different URIs.

  3. Finally, the manifest contains zero or more xsl:expose declarations that define the interface offered by this package to the outside world.

A package that does not itself expose any components (in effect, a stylesheet that makes use of library packages but is not itself intended to act as a library package) may be written using a simplified syntax: the xsl:package element is omitted, and the xsl:use-package children are moved to the xsl:stylesheet or xsl:transform element, which is now the outermost element of the stylesheet module. More formally, an xsl:stylesheet or xsl:transform element having one or more xsl:use-package children is equivalent to the package represented by the output of the following transformation, preserving the base URI of the source:

 <xsl:transform version="3.0" 
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:t="http://www.w3.org/1999/XSL/TransformAlias">
 
    <xsl:namespace-alias stylesheet-prefix="t" result-prefix="xsl"/>
    <xsl:mode on-no-match="shallow-copy"/>
    <xsl:template match="(xsl:stylesheet|xsl:transform)[xsl:use-package]">
      <t:package version="{@version}">
        <xsl:copy-of select="xsl:use-package"/>
        <xsl:copy>
          <xsl:copy-of select="@*"/>
          <xsl:copy-of select="* except xsl:use-package"/>
        </xsl:copy>
      </t:package>
    </xsl:template>
 </xsl:transform>   
       

The effect of the input-type-annotations attribute is defined in 4.3 Stripping Type Annotations from a Source Tree.

3.6.1 Dependencies between Packages

When components in one package reference components in another, the dependency of the first package on the second must be represented by an xsl:use-package element in the package manifest of the first package.

[Definition: If a package Q contains an xsl:use-package element that references package P, then package Q is said to use package P. In this relationship package Q is referred to as the using package, package P as the used package.]

The phrase directly uses is synonymous with uses as defined above, while directly or indirectly uses refers to the transitive closure of this relationship.

<xsl:use-package
  name = uri
  package-version? = token >
  <!-- Content: (xsl:accept | xsl:override)* -->
</xsl:use-package>

A package may be used by more than one other package, but the relationship must not be cyclic. It is possible, but by no means inevitable, that using the same package in more than one place within a stylesheet will cause static errors due to the presence of conflicting components according to the above rules. Where a package is successfully used by more than one other package, its components may be overridden in different ways by different using packages.

The name and package-version attributes together identify the used package. The used package must have a name that is an exact match for the name in the name attribute (using codepoint comparison), and it may have a package-version that matches the pattern given in the package-version attribute, according to the rules below. Omitting this attribute is equivalent to specifying the value as package-version="#", which matches any version.

The value of the package-version attribute consists of a prefix and a suffix separated by a hash sign (#); if there is no hash sign, the entire string is used as the prefix, and the suffix is empty; if there is more than one hash sign, the first one is taken as the separator and others as part of the suffix; if the hash sign is the last character in the string then a suffix of ".*" is assumed. The pattern matches a package version if the package version can be divided into two substrings such that the first substring matches the prefix literally (using codepoint comparison), and the second substring matches the suffix considered as a regular expression (matched according to the rules of the matchesFO30 function with the $flags argument set to a zero length string). Thus the version pattern 3.1 matches version 3.1 only; the pattern 3.1# matches 3.1, 3.1.2, and 3.17; the pattern 3.1#(\.\d+)? matches 3.1 and 3.1.5; and the pattern 3.1#(\.\d+)* matches 3.1, 3.1.5, and 3.1.5.2.

This specification does not define how the implementation locates a package given its name and version. Nor does it define whether this process locates source code or some other representation of the package contents. Such mechanisms are implementation-defined. Use of the package name as a dereferencable URI is not recommended, because the intent of the packaging feature is to allow a package to be distributed as reusable code and therefore to exist in many different locations.

The xsl:accept and xsl:override elements are used to modify the visibility or behavior of components acquired from the used package; they are described in 3.6.2.4 Accepting Components below.

An xsl:use-package element whose parent element is xsl:stylesheet or xsl:transform is allowed only if the xsl:stylesheet or xsl:transform does not form part of an explicit package.

3.6.2 Named Components in Packages

This section discusses the use of named components in packages: specifically functions, named templates, attribute sets, modes, accumulators, keys, modes, and global variables and parameters. Some of the provisions in this section also apply to named modes, but there are differences noted in 3.6.3 Overriding Template Rules from a Used Package. The section is largely concerned with details of the rules that affect references from one component to another by name, whether the components are in the same package or in different packages. The rules are designed to meet a number of requirements:

  • A component defined in one package can be overridden by a component in another package, provided the signatures are type-compatible.

  • The author of a package can declare whether the components in the package are public or private (that is, whether or not they can be used from outside the package) and whether they are final, overridable, or abstract (that is whether they can or must be overridden by the using package).

  • Within an application, two packages can make use of a common library and override its components in different ways.

  • Visibility of components can be defined either as part of the declaration of the component, or in the package manifest.

  • An application that wishes to make use of a library package can be selective about which components from the library it acquires, perhaps to avoid name clashes between components acquired from different libraries.

[Definition: The term component is used to refer to any of the following: a stylesheet function, a named template, a mode, an accumulator an attribute set, a key, global variable, or a mode.]

[Definition: The symbolic identifier of a component is a composite name used to identify the component uniquely within a package. The symbolic identifier comprises the kind of component (stylesheet function, named template, accumulator, attribute set, global variable, or mode), the expanded QName of the component (namespace URI plus local name), and in the case of stylesheet functions, the arity.]

[Definition: Two components are said to be homonymous if they have the same symbolic identifier.]

Every component has a declaration in some stylesheet module and therefore within some package. In the case of attribute sets, there may be several declarations. The declaration is an element in an XDM tree representing the stylesheet module. Declarations therefore have identity, based on XDM node identity.

Not all declarations result in components:

  • Some declarations, such as xsl:decimal-format and xsl:strip-space, declare aspects of the processing context which are not considered to be components as defined here.

  • Template rules (xsl:template with a match attribute) are also not considered to be components for the purposes of this section, which is concerned only with components that are bound by name. However, when an xsl:template has both a match attribute and a name attribute, then it establishes both a template rule and a named template, and in its role as a named template it comes within the scope of this discussion.

  • A named declaration, for example a named template, a function, an accumulator, or a global variable, may be overridden within the same package by another like-named declaration having higher import precedence. When a declaration is overridden in this way it can never be referenced or invoked either from within its containing package or from outside that package; it is effectively dead code, and it therefore does not result in the creation of any component, which means that it plays no part in the component binding process.

  • In the case of xsl:attribute-set and xsl:key declarations, several declarations combine to form a single component.

[Definition: The declaring package of a component is the package that contains the declaration (or, in the case of xsl:attribute-set and xsl:key, multiple declarations) of the component.]

When a component declared in one package is made available in another, the using package will contain a separate component that can be regarded as a modified copy of the original. The new component shares the same symbolic identifier as the original, and it has the same declaration, but it has other properties such as its visibility that may differ from the original.

[Definition: A component declaration results in multiple components, one in the package in which the declaration appears, and potentially one in each package that uses the declaring package, directly or indirectly, subject to the visibility of the component. Each of these multiple compenents has the same declaring package, but each has a different containing package. For the original component, the declaring package and the containing package are the same; for a copy of a component made as a result of a xsl:use-package declaration, the declaring package will be the original package, and the containing package will be the package in which the xsl:use-package declaration appears.]

The properties of a component are as follows:

Note:

When a function F defined in a package P is acquired by two using packages Q and R, we may think of P, Q, and R as all providing access to the "same" function. The detailed semantics, however, demand an understanding that there is one function declaration, but three components. The three components representing the function F within packages P, Q, and R have some properties in common (the same symbolic identifier, the same declaration), but other properties (the visibility and the bindings of symbolic references) that may vary from one of these components to another.

[Definition: The declaration of a component includes constructs that can be interpreted as references to other components by means of their symbolic identifiers. These constructs are generically referred to as symbolic references. Examples of constructs that give rise to symbolic references are the name attribute of xsl:call-template; the [xsl:]use-attribute-sets attribute of xsl:copy, xsl:element, and literal result elements; the mode attribute of xsl:template and xsl:apply-templates; XPath variable references referring to global variables; and XPath function calls referring to stylesheet functions or accumulator functions.]

Symbolic references exist as properties of the declaration of a component. The symbolic identifier being referred to can be determined straightforwardly from the syntactic form and context of the reference: for example, the instruction <xsl:value-of select="f:price($o)" xmlns:f="http://f.com/"/> contains a symbolic reference to a function with expanded name {http://f.com/}price and with arity=1. However, because there may be several (homonymous) function components with this symbolic identifier, translating this symbolic reference into a reference to a specific component (a process called "binding") is less straightforward, and is described in the text that follows.

The process of assembling a stylesheet from its constituent packages is primarily a process of binding these symbolic references to actual components. Within any component whose declaration is D, there is a set of bindings; each binding is an association between an symbolic reference in D and a component whose symbolic identifier matches the outward reference. Outward references for which a component C contains a binding are said to be bound in C; those for which C contains no binding are said to be unbound.

For example, suppose that in some package P, function A calls B, which in turn calls C, and that B is private. Now suppose that in some package Q which uses P, C is overridden. The effect of the binding process is that Q will contain three components corresponding to A, B, and C, which we might call A(Q), B(Q), and C(Q). The declarations of A(Q) and B(Q) are in package P, but the declaration of C(Q) is in Q. The internal visibility of B(Q) will be hidden (meaning that it cannot be referenced from within Q), and B(Q) will contain a binding for the component C(Q) that corresponds to the outward reference from B to C. The effect is that when A calls B and B calls C, it is the overriding version of C that is executed. In another package R that uses P without overriding C, there will be three different components A(R), B(R), and C(R). This time the declaration of all three components is in the original package P. Component B(R) will contain a binding to C(R), so in this package, the original version of C is executed. The fact that one package Q overrides C thus has no effect on R, which does not override it.

Template rules are not components in their own right; unlike named templates, they are never referenced by name. Component references within a template rule (for example, references to functions, global variables, or named templates) are treated as occurring within the component that represents the containing mode. If a template rule lists several modes, it is treated as if there were multiple template rules one in each mode.

Keys behave rather differently from other components. Their visibility is always private, which means they can only be used within their declaring package. In addition, the component binding (the reference to a key definition from a call on the key function) is in the general case made dynamically rather than statically. However, outward references from key definitions to other components (such as global variables and functions) behave in the same way as component references contained in any other private component, in that they may be rebound to an overriding declaration of the target component.

3.6.2.1 Visibility of Components

[Definition: The visibility of a component is one of: private, public, abstract, final, or hidden.]

The meanings of these visibility values is as follows:

Visibility Meaning
public The component can be referenced from other components in this package or in any using package; it can be overridden by a different component in any using package.
private The component can be referenced from other components in this package; it cannot be referenced or overridden within a using package.
abstract The component can be referenced from other components in this package or in any using package; in a using package it can either remain abstract or be overridden by a different component.
final The component can be referenced from other components in this package or in any using package; it cannot be overridden by a different component in any using package.
hidden The component cannot be referenced from other components in this package; it cannot be referenced or overridden within a using package.

The visibility (sometimes called the actual visibility) of a component depends on two factors: its potential visibility and its exposed visibility.

[Definition: The potential visibility of a component is established when the component is declared or accepted into a package.]

[Definition: The exposed visibility of a component is established by an xsl:expose element in the package manifest.]

For a component within its declaring package the potential visibility is the value of the visibility attribute on the component's declaration, or private if the attribute is absent.

For a component accepted from another package, the potential visibility depends on the visibility declared in the relevant xsl:accept or xsl:override element that makes the component available within the using package; this in turn has a default that depends on the (actual) visibility of the corresponding component in the used package.

These rules are described more fully in the sections that follow.

3.6.2.2 Visibility of Declarations

The xsl:function, xsl:template, xsl:attribute-set, xsl:variable, xsl:param, and xsl:mode declarations each have an optional visibility attribute that determines the potential visibility of the component corresponding to this declaration in its declaring package. The value is one of private, public, abstract, final (never hidden), with the default being private. In the case of xsl:attribute-set, all the declarations for an attribute set must have the same value for the visibility attribute. In the case of xsl:key, the visibility cannot be explicitly specified: it is always private.

Whatever the value of this attribute, and whatever the exposed visiblity of the component, other declarations within the same package may contain symbolic references to this declaration: informally, the name of the component is always "in scope" within the package containing its declaration. The way in which these symbolic references are bound to an actual component, however, depends on the component's visibility, as defined in 3.6.2.6 Binding References to Components. For example, a symbolic reference will never be bound to a component whose visibility is abstract.

3.6.2.3 Exposing Components

The visibility of a component within a package may be modified by means of an xsl:expose element in the package manifest.

<xsl:expose
  component = "template" | "function" | "accumulator" | "attribute-set" | "variable" | "mode"
  names = tokens
  visibility = "public" | "private" | "final" | "abstract" />

The xsl:expose element allows selected components within a package to have an exposed visibility different from their potential visibility .

The components in question are identified using their symbolic identifiers. The component attribute defines the kind of component that is selected (variable embraces xsl:variable and xsl:param). The names attribute selects a subset of those components by name (and in the case of functions, arity); its value is a whitespace-separated sequence of tokens each of which is either a NameTestXP30 or a NamedFunctionRefXP30. (Examples are *, p:*, *:local, p:local, and p:local#2.)

The value may be a NamedFunctionRef only in the case of stylesheet functions, and distinguishes functions with the same name and different arity.

The visibility attribute defines the exposed visibility of the selected components.

If a component is matched by more than one xsl:expose element in the package manifest, then its exposed visibility is determined by the best matching NameTestXP30 or LiteralFunctionItem. The rules are similar to those for template rules:

  • A token in the form of a LiteralFunctionItem (for example, f:price#1) has higher priority than any NameTest.

  • Next, any match that has a lower default priority than the default priority of another match is ignored.

  • If several matches have the same default priority (which can happen if the same value is repeated, or if one of the NameTests takes the form *:local and the other takes the form prefix:*), then the xsl:expose element that appears last in document order within the package manifest is used.

If no xsl:expose element matches a component, then the visibility of the component is its potential visibility.

Otherwise, the visibility of the component depends on its potential visibility and its exposed visibility as defined by the following table. In this table, the value N/P means "not permitted".

Exposed visibility Potential visibility
public private final abstract
public public N/P N/P N/P
private private private private N/P
final final N/P final N/P
abstract N/P N/P N/P abstract

[ERR XTSE3010] It is a static error if the exposed visibility of a component is inconsistent with its potential visibility, as defined in the above table, unless the token that matches the component is a wildcard, in which case it is treated as not matching that component.

[ERR XTSE3020] It is a static error if an xsl:expose element matches no components in the containing package, unless the tokens in the names attribute are all wildcards.

3.6.2.4 Accepting Components

When a package Q uses a package P, by virtue of an xsl:use-package element in the package manifest of Q, then Q will contain a component corresponding to every component in P. The potential visibility of the component within Q depends on the visibility of the component in P, optionally modified by two elements that may appear as children of the xsl:use-package element, namely xsl:accept and xsl:override.

For every component C(P) in package P that is not matched by any xsl:override or xsl:accept element in the package manifest of Q, there will be a corresponding component C(Q) in package Q that has the same symbolic identifier and declaration as C(P). The potential visibility of C(Q) will be the same as the (actual) visibility of C(P), except that where the visibility of C(P) is private, the potential visibility of C(Q) will be hidden. The (actual) visibility of C(Q) depends both on its potential visibility and its exposed visibility, as described in 3.6.2.3 Exposing Components.

A component C(P) in package P whose visibility is hidden will never be matched by an xsl:override or xsl:accept element in the package manifest of Q, and therefore Q will contain a hidden component C(Q) corresponding to C(P).

<xsl:accept
  component = "template" | "function" | "accumulator" | "attribute-set" | "variable" | "mode"
  names = tokens
  visibility = "public" | "private" | "final" | "abstract" | "hidden" | "absent" />

The xsl:accept element has the same syntax as xsl:expose, and very similar semantics. Whereas xsl:expose allows a package to restrict the visibility of its own components to other (using) packages, xsl:accept allows a package to restrict the visibility of components exposed by a package that it uses. This may be necessary if, for example, it uses two different packages whose component names conflict. It may also simply be good practice if the package author knows that only a small subset of the functionality of a used package is required.

The rules for determining whether an xsl:accept element matches a particular component, and for which element to use if there are several matches, are the same as the rules for the xsl:expose element.

[ERR XTSE3030] It is a static error if an xsl:accept element matches no components in the used package, unless the tokens in its names attribute are all wildcards.

In the absence of a matching xsl:override element (see 3.6.2.5 Overriding Named Components from a Used Package), the potential visibility of a component that matches an xsl:accept element depends both on the visibility attribute of the best-matching xsl:accept element and on the (actual) visibility of the corresponding component in the used package, according to the following table. In this table the entry "N/P" means "not permitted".

Visibility in xsl:accept element Visibility in used package
public private final abstract
public public N/P N/P N/P
private private N/P private N/P
final final N/P final N/P
abstract N/P N/P N/P abstract
hidden hidden N/P hidden N/P
absent N/P N/P N/P absent

[ERR XTSE3040] It is a static error if the visibility assigned to a component by an xsl:accept element is incompatible with the visibility of the corresponding component in the used package, as defined by the above table, unless the token that matches the component name is a wildcard, in which case the xsl:accept element is treated as not matching that component.

[ERR XTSE3050] It is a static error if the xsl:use-package elements in a package manifest cause two or more homonymous components to be accepted with a visibility other than hidden.

Conflicts between the components accepted from used packages and those declared within the package itself are handled as follows:

  1. If the conflict is between two components both declared within the package itself, then it is resolved by the rules relating to import precedence defined for each kind of component.

  2. If the conflict is between two components both accepted from used packages, or between a component declared within the package and an accepted component, then a static error occurs.

The value visibility="absent" may be used only in the case of a component that is present in the used package with exposed visibility abstract. It is used to indicate that the using package does not intend to provide an implementation of the abstract component, and that any invocation of the abstract component is therefore to result in an error. Specifically:

  1. Any component reference to the component within the using package is a static error, as if the component were hidden: in effect, the name of the component is not in scope in the using package.

  2. Any invocation of the absent component (typically from within its declaring package) causes a dynamic error, as if the component were overridden by a component that unconditionally raises a dynamic error.

    [ERR XTDE3052] It is a dynamic error if an invocation of an absent component (that is, an abstract component accepted into a using package with visibility="absent") is evaluated.

Note:

To override a component accepted from a used package, the overriding declaration must appear as a child of the xsl:override element.

Note:

There is no rule that prevents a function (say) being declared in the using package with the same name as a private function in the used package. This does not create a conflict, since all references in the used package are bound to one function and all those in the using package are bound to another.

3.6.2.5 Overriding Named Components from a Used Package

[Definition: A component in a using package may override a component in a used package, provided that the visibility of the component in the used package is either abstract or public. The overriding declaration is written as a child of the xsl:override element, which in turn appears as a child of xsl:use-package.]

<xsl:override>
  <!-- Content: (xsl:template | xsl:function | xsl:accumulator | xsl:variable | xsl:param | xsl:attribute-set)* -->
</xsl:override>

Note:

This mechanism is distinct from the mechanism for overriding declarations within the same package by relying on import precedence. It imposes stricter rules: the overriding component is required to be type-compatible with the component that it overrides.

If the used package P contains a component C(P) and the xsl:use-package element contains an xsl:override element which contains a declaration D whose symbolic identifier matches the symbolic identifier of C(P), then the using package Q will contain a component whose declaration is D, whose symbolic identifier is that of D, and whose potential visibility is equal to the value of the visibility attribute of D, or private if this is absent.

If the overridden component C(P) has visibility public then the using package Q will also contain a component C′(Q) whose declaration is the same as the declaration of C(P) and whose visibility is hidden. This component is used as the target of a binding for the symbolic reference xsl:original described below.

Other than its appearance as a child of xsl:override, the overriding declaration is a normal xsl:function, xsl:template, xsl:accumulator, xsl:variable, xsl:param, xsl:attribute-set, or xsl:mode element. In the case of xsl:variable and xsl:param, the variable that is declared is a global variable.

The potential visibility of the overriding component in the using package is defined by the visibility attribute appearing on the overriding declaration.

[ERR XTSE3055] It is a static error if a component declaration appearing as a child of xsl:override is homonymous with any other declaration in the using package, regardless of import precedence, including any other overriding declaration in the package manifest of the using package.

Note:

When an attribute set is overridden, the overriding attribute set must be defined using a single xsl:attribute-set element. Attribute sets defined in different packages are never merged by virtue of having the same name, though they may be merged explicitly by using the use-attribute-sets attribute.

[ERR XTSE3058] It is a static error if a component declaration appearing as a child of xsl:override does not match (is not homonymous with) some component in the used package.

[ERR XTSE3060] It is a static error if the component referenced by an xsl:override declaration has visibility other than public or abstract

A package is executable if and only if it contains no component whose visibility is abstract. A package that is not executable is not a stylesheet, and therefore cannot be nominated as the stylesheet to be used when initiating a transformation.

Note:

In other words, if a component is declared as abstract, then some package that uses the declaring package of that component directly or indirectly must override that component with one that is not abstract. It is not necessary for the override to happen in the immediately using package.

[ERR XTSE3070] It is a static error if the signature of an overriding component is not compatible with the signature of the component that it is overriding.

[Definition: The signatures of two components are compatible if they present the same interface to the user of the component. The additional rules depend on the kind of component.]

Compatibility is only relevant when comparing two components that have the same symbolic identifier. The compatibility rules for each kind of component are as follows:

  • Two attribute sets with the same name are compatible if and only if they satisfy the following rule:

    1. If the overridden attribute set specifies streamable="yes" then the overriding attribute set also specifies streamable="yes".

  • Two functions with the same name and arity are compatible if and only if they satisfy all the following rules:

    1. The types of the arguments are pairwise identical.

    2. The return types are identical.

    3. If the overridden function specifies identity-sensitive="no" then the overriding function also specifies identity-sensitive="no".

    4. If the overridden function specifies override-extension-functions="no" (or the equivalent using the deprecated override attribute) then the overriding function also specifies override-extension-functions="no" (or the equivalent).

  • Two accumulators with the same name are compatible if and only if they satisfy all the following rules:

    1. The types (defined in the as attribute) are identical.

    2. If the overridden accumulator specifies streamable="yes" then the overriding accumulator also specifies streamable="yes".

  • Two named templates with the same name are compatible if and only if they satisfy all the following rules:

    1. Their return types are identical.

    2. For every parameter on the overridden template, there is a parameter on the overriding template that has the same name, an identical required type, and the same effective values for the tunnel and required attributes.

    3. Any parameter on the overriding template for which there is no corresponding parameter on the overridden template specifies required="no".

    4. The two templates have equivalent xsl:context-item children, where equivalence means that the use attributes are the same and the required types are identical; an absent xsl:context-item is equivalent to one that specifies use="optional" and as="item()".

  • Two variables (including parameters) with the same name are compatible if and only if they satisfy all the following rules:

    1. Their declared types are identical.

    2. If the overridden variable is a parameter that specifies required="yes" then the overriding variable is either a non-parameter variable, or a parameter that specifies required="yes"

    Note:

    A variable may override a parameter or vice-versa, and the initial value may differ.

    Because static variables and parameters are constrained to have visibility private or final, they cannot be overridden in another package. The compatibility rules therefore do not arise. The reason that such variables cannot be overridden is that they are typically used during stylesheet compilation (for example, in [xsl:]use-when expressions) and it is a design goal that packages should be capable of independent compilation.

[Definition: Types S and T are considered identical for the purpose of these rules if and only if subtype(S, T) and subtype(T, S) both hold, where the subtype relation is defined in Section 2.5.6.1 The judgement subtype(A, B) XP30.]

Note:

  1. One consequence of this rule is that two plain union types are considered identical if they have the same set of member types, even if the union types have different names or the ordering of the member types is different.

  2. While this rule may appear formal, it is not as straightforward as might be supposed, because the subtype relation in XPath has a dependency on the "Type derivation OK (Simple)" relation in XML Schema, which itself appeals to a judgement as to whether the two type definitions being compared "are the same type definition". Both XSD 1.0 and XSD 1.1 add the note "The wording of [this rule] appeals to a notion of component identity which is only incompletely defined by this version of this specification." However, they go on to say that component identity is well defined if the components are named simple type definitions, which will always apply in this case. For named atomic types, the final result of these rules is that two atomic types are identical if and only if they have the same name.

Modes are not overridable, so the xsl:mode declaration cannot appear as a child of xsl:override.

Within the declaration of an overriding component (that is, a component whose declaration is a child of xsl:override), where the overridden component has public visibility, it is possible to use the name xsl:original as a symbolic reference to the overridden component:

  • Within an overriding named template, <xsl:call-template name="xsl:original"/> may be used to call the overridden named template.

  • Within an overriding stylesheet function, xsl:original() may be used to call the overridden stylesheet function.

  • Within an overriding global variable or parameter, $xsl:original may be used to reference the overridden global variable or parameter.

  • Within an overriding attribute set, [xsl:]use-attribute-set="xsl:original" may be used to reference the overridden attribute set.

  • Within an overriding accumulator, however, it is not possible to refer to the overridden accumulator.

Within the overriding component C(Q), this symbolic reference is bound to the hidden component C′(Q) described earlier, whose declaration is that of the component C(P) in the used package. The static context for the overriding declaration is augmented to include a component of the relevant kind (function, named template, attribute set, or variable) with the name xsl:original.

3.6.2.6 Binding References to Components

[Definition: The process of identifying the component to which a symbolic reference applies (possibly chosen from several homonymous alternatives) is called reference binding.] A reference is called bound if the component to which it applies has been identified and fixed, and is unbound otherwise (that is, if it exists only in the form of a symbolic identifier).

Reference resolution for the components in a package occurs conceptually after a package has been fully defined and before the processing of any other package that uses it.

Note:

If packages are separately compiled, then reference resolution is likely to form part of the compilation process.

When reference resolution is performed for a component C, each symbolic reference R that is present in the declaration of C is processed as follows:

  1. If C already contains a binding for R then this binding is retained.

  2. If C contains no binding for R then the processor attempts to locate a component in the containing package of C whose visibility is not hidden and whose symbolic name matches R. If there is no such component, then a static error is reported as described elsewhere in this specification. There can never be more than one. Call the located component D. If D has visibility private or final, then C acquires a binding that associates the symbolic reference R with the component D. Otherwise, the reference remains unbound.

When a package P is used by another package Q, then Q will accept components corresponding to the components in P, as described in previous sections. Until reference resolution is performed for Q, these components will have the same bindings as their corresponding components from P: a symbolic reference that was bound for a component in P will retain the same binding, and a symbolic reference that was unbound in P will remain unbound in the corresponding component in Q. Subsequently, when reference resolution is performed for package Q, these symbolic references may become bound, perhaps to components whose declaration is in Q or in some other package.

When reference resolution is performed on a package that is intended to be used as a stylesheet (that is, for the top-level package), symbolic references to components whose visibility is public are bound in the same way as references to components whose visibility is private or final. At this stage there must be no symbolic references referring to components whose visibility is abstract (that is, an implementation must be provided for every abstract component).

[ERR XTSE3080] It is a static error if a top-level package intended for execution (as distinct from a library package) contains symbolic references referring to components whose visibility is abstract.

Note:

Unresolved references are allowed at the module level but not at the package level. A stylesheet module can contain references to components that are satisfied only when the module is imported into another module that declares the missing component.

Note:

The process of resolving references (or linking) is critical to an implementation that uses separate compilation. One of the aims of these rules is to ensure that when compiling a package, it is always possible to determine the signature of called functions, templates, and other components. A further aim is to establish unambiguously in what circumstances components can be overridden, so that compilers know when it is possible to perform optimizations such as inlining of function and variable references.

Suppose a public template T calls a private function F. When the package containing these two components is referenced by a using package, the template remains public, while the function becomes hidden. Because the function becomes hidden, it can no longer conflict with any other function of the same name, or be overridden by any other function; at this stage the compiler knows exactly which function T will be calling, and can perform optimizations based on this knowledge.

The mechanism for resolving component references described in this section is consistent with the mechanism used for binding function and variable references described in the XPath specification. XPath requires these variable and function names to be present in the static context for an XPath expression. XSLT ensures that all the non-hidden functions, global variables, and global parameters in a package are present in the static context for every XPath expression that appears in that package, along with required information such as the type of a variable and the signature of a function.

3.6.3 Overriding Template Rules from a Used Package

The rules in the previous section apply to named components including functions, named templates, global variables, and named attribute sets. The rules for modes, and the template rules appearing within a mode, are slightly different.

The unnamed mode is local to a package: in effect, each package has its own private unnamed mode, and the unnamed mode of one package does not interact with the unnamed mode of any other package.

A named mode may be declared in an xsl:mode declaration as being either public, private, or final. The values of the visibility attribute are interpreted as follows:

Value Meaning
public A using package may use xsl:apply-templates to invoke templates in this mode; it may also declare additional template rules in this mode, which are selected in preference to template rules in the used package. These may appear only as children of the xsl:override element within the xsl:use-package element.
private A using package may neither reference the mode nor provide additional templates in this mode; the name of the mode is not even visible in the using package, so no such attempt is possible. The using package can use the same name for its own modes without risk of conflict.
final A using package may use xsl:apply-templates to invoke templates in this mode, but it must not provide additional template rules in this mode.

As with other named components, an xsl:use-package declaration may contain an xsl:expose element to control the visibility of a mode acquired from the used package. The allowed values of its visibility attribute are public, private, final, and hidden.

The xsl:mode declaration itself must not be overridden. A using package must not contain an xsl:mode declaration whose name matches that of a public or final xsl:mode component accepted from a used package.

The xsl:expose and xsl:accept elements may be used to reduce the visibility of a mode in a using package; the same rules apply in general, though some of the rules are not applicable because, for example, modes cannot be abstract.

It is not possible for a package to combine the template rules from two other packages into a single mode. When xsl:apply-templates is used without specifying a mode, the chosen template rules will always come from the same package; when it is used with a named mode, then they will come from the package where the mode is defined, or any package that uses that package and adds template rules to the mode. If two template rules defined in different packages match the same node, then the rule in the using package wins over any rule in the used package; this decision is made before taking other factors such as import precedence and priority into account.

A static error occurs if two modes with the same name are visible within a package, either because they are both declared within the package, or because one is declared within the package and the other is acquired from a used package, or because both are accepted from different used packages.

The rules for matching template rules by precedence and priority operate as normal, with the addition that template rules declared within an xsl:use-package element have higher precedence than any template rule declared in the used package.

When a template rule specifies mode="#all" this is interpreted as meaning all modes declared implicitly or explicitly within the declaring package of the xsl:template element.

Note:

If existing XSLT code has been written to use template rules in the unnamed mode, a convenient way to incorporate this code into a library package is to add a stub module that defines a new named public or final mode, in which there is a single template rule whose content is the single instruction <xsl:apply-templates/>. This in effect redirects xsl:apply-templates instructions using the named mode to the rules defined in the unnamed mode.

3.6.4 Declarations Local to a Package

Declarations of keys, decimal formats, namespace aliases (see 11.1.5 Namespace Aliasing), output definitions, and character maps within a package have local scope within that package — they are all effectively private. The elements that declare these constructs do not have a visibility attribute. The unnamed decimal format and the unnamed output format are also local to a package.

If xsl:strip-space or xsl:preserve-space declarations appear within a library package, they only affect calls to the docFO30 or document functions appearing within that package. Such a declaration within the main package additionally affects stripping of whitespace in the principal source document.

An xsl:decimal-format declaration within a package applies only to calls on format-numberFO30 appearing within that package.

An xsl:namespace-alias declarations within a package applies only to literal result elements within the same package.

An xsl:import-schema declaration within a package adds the names of the imported schema components to the static context for that package only; these names are effectively private, in the sense that they do not become available for use in any other packages. However, the names of schema components must be consistent across the stylesheet as a whole: it is not possible for two different packages within a stylesheet to use a type-name such as "part-number" to refer to different schema-defined simple or complex types.

Type names used in the interface of public components in a package (for example, in the arguments of a function) must be respected by callers of those components, in the sense that the caller must supply values of the correct type. Often this will mean that the using component, if it contains calls on such interfaces, must itself import the necessary schema components. However, the requirement for an explicit schema import applies only where the package contains explicit use of the names of schema components required to call such interfaces.

Note:

For example, suppose a library package contains a function which requires an argument of type mfg:part-number. The caller of this function must supply an argument of the correct type, but does not need to import the schema unless it explicitly uses the schema type name mfg:part-number. If it obtains an instance of this type from outside the package, for example as the result of another function call, then it can supply this instance to the acquired function even though it has not imported a schema that defines this type.

At execution time, the schema available for validating instance documents contains (at least) the union of the schema components imported into all constituent packages of the stylesheet.

3.6.5 Using an XQuery Library Package

The capability described in this section is an optional feature that processors are not required to provide.

A processor may recognize the URI supplied in the name attribute of an xsl:use-package element as the module URI of an XQuery library module.

In this case all public functions and global variables declared in the XQuery library module become available for use in the using package as if they were declared as public functions or global variables in an XSLT 3.0 package. XQuery external variables are treated as if they were XSLT stylesheet parameters.

There are some minor differences in semantics between XSLT and XQuery, for example XSLT uses the function conversion rules when initializing a global variable (in XSLT, a node will be atomized if the required type is atomic) whereas XQuery requires the computed value to match the declared type precisely. The way in which such differences are handled is implementation-defined; a conformant implementation may use either the XQuery semantics or the XSLT semantics.

It is implementation-defined whether an XQuery expression that is evaluated in the course of a transformation is evaluated within the same execution scopeFO30 as the calling XSLT code. (It if is, then, for example, calls to current-dateTime will deliver the same result whether called from the XSLT code or the XQuery code.)

It is implementation-defined whether node identity is preserved when calling XQuery code from XSLT code.

Note:

Where the XSLT implementation invokes an XQuery processor developed by a third party, it may be necessary to convert nodes to a different internal representation as part of the calling mechanism, and it may be difficult to do this conversion in a way that retains node identity. It is required, however, that nodes passed to the XQuery processor, or returned in the result, retain all their relationships to other nodes in the same tree. Furthermore, this specification provides no license to drop type annotations.

As when using multiple XSLT packages, it is required that any schema imported by the XQuery library module must be consistent with the schema imported by the using package, and that any type annotation on a node passed from one package to another must refer unambiguously to the same type.

The effect of using an XQuery library module in which there are functions that are updating or nondeterministic is implementation-defined.

Processors may impose additional restrictions on the use of XQuery library modules; for example they may treat variables and functions declared in the library module as final, or they may require that the module uses a particular version of XQuery.

3.7 Stylesheet Modules

[Definition: A package consists of one or more stylesheet modules, each one forming all or part of an XML document.]

Note:

A stylesheet module is represented by an XDM element node (see [Data Model]). In the case of a standard stylesheet module, this will be an xsl:stylesheet or xsl:transform element. In the case of a simplified stylesheet module, it can be any element (not in the XSLT namespace) that has an xsl:version attribute.

Although stylesheet modules will commonly be maintained in the form of documents conforming to XML 1.0 or XML 1.1, this specification does not mandate such a representation. As with source trees, the way in which stylesheet modules are constructed, from textual XML or otherwise, is outside the scope of this specification.

A stylesheet module is either a standard stylesheet module or a simplified stylesheet module:

  • [Definition: A standard stylesheet module is a tree, or part of a tree, consisting of an xsl:stylesheet or xsl:transform element (see 3.8 Stylesheet Element) together with its descendant nodes and associated attributes and namespaces.]

  • [Definition: A simplified stylesheet module is a tree, or part of a tree, consisting of a literal result element together with its descendant nodes and associated attributes and namespaces. This element is not itself in the XSLT namespace, but it must have an xsl:version attribute, which implies that it must have a namespace node that declares a binding for the XSLT namespace. For further details see 3.9 Simplified Stylesheet Modules. ]

Both forms of stylesheet module (standard and simplified) can exist either as an entire XML document, or embedded as part of another XML document, typically but not necessarily a source document that is to be processed using the stylesheet.

[Definition: A standalone stylesheet module is a stylesheet module that comprises the whole of an XML document.]

[Definition: An embedded stylesheet module is a stylesheet module that is embedded within another XML document, typically the source document that is being transformed.] (see 3.13 Embedded Stylesheet Modules).

There are thus four kinds of stylesheet module:

standalone standard stylesheet modules
standalone simplified stylesheet modules
embedded standard stylesheet modules
embedded simplified stylesheet modules

3.8 Stylesheet Element

<xsl:stylesheet
  id? = id
  version? = decimal
  default-mode? = eqname | "#unnamed"
  default-validation? = "preserve" | "strip"
  input-type-annotations? = "preserve" | "strip" | "unspecified"
  default-collation? = uris
  extension-element-prefixes? = prefixes
  exclude-result-prefixes? = prefixes
  expand-text? = "yes" | "no"
  use-when? = expression
  xpath-default-namespace? = uri >
  <!-- Content: (xsl:use-package*, other-declarations) -->
</xsl:stylesheet>

<xsl:transform
  id? = id
  version? = decimal
  default-mode? = eqname | "#unnamed"
  default-validation? = "preserve" | "strip"
  input-type-annotations? = "preserve" | "strip" | "unspecified"
  default-collation? = uris
  extension-element-prefixes? = prefixes
  exclude-result-prefixes? = prefixes
  expand-text? = "yes" | "no"
  use-when? = expression
  xpath-default-namespace? = uri >
  <!-- Content: (xsl:use-package*, other-declarations) -->
</xsl:transform>

A stylesheet module is represented by an xsl:stylesheet element in an XML document. xsl:transform is allowed as a synonym for xsl:stylesheet; everything this specification says about the xsl:stylesheet element applies equally to xsl:transform.

The version attribute indicates the version of XSLT that the stylesheet module requires. The attribute is required, unless the xsl:stylesheet element is a child of an xsl:package element, in which case it is optional: the default is then taken from the parent xsl:package element.

[ERR XTSE0110] The value of the version attribute if present must be a number: specifically, it must be a valid instance of the type xs:decimal as defined in [XML Schema Part 2].

The version attribute is intended to indicate the version of the XSLT specification against which the stylesheet is written. In a stylesheet written to use XSLT 3.0, the value should normally be set to 3.0. If the value is numerically less than 3.0, the stylesheet is processed using the rules for backwards compatible behavior (see 3.10 Backwards Compatible Processing). If the value is numerically greater than 3.0, the stylesheet is processed using the rules for forwards compatible behavior (see 3.11 Forwards Compatible Processing).

The effect of the input-type-annotations attribute is described in 4.3 Stripping Type Annotations from a Source Tree.

The [xsl:]default-validation attribute defines the default value of the validation attribute of all relevant instructions appearing within its scope. For details of the effect of this attribute, see 24.2 Validation.

[ERR XTSE0120] An xsl:stylesheet element must not have any text node children. (This rule applies after stripping of whitespace text nodes as described in 4.2 Stripping Whitespace from the Stylesheet.)

[Definition: An element occurring as a child of an xsl:stylesheet, xsl:transform, or xsl:override element is called a top-level element.]

[Definition: Top-level elements fall into two categories: declarations, and user-defined data elements. Top-level elements whose names are in the XSLT namespace are declarations. Top-level elements in any other namespace are user-defined data elements (see 3.8.3 User-defined Data Elements)].

The declaration elements permitted in the xsl:stylesheet element are:

xsl:use-package
xsl:import
xsl:include
xsl:accumulator
xsl:attribute-set
xsl:character-map
xsl:decimal-format
xsl:function
xsl:import-schema
xsl:key
xsl:mode
xsl:namespace-alias
xsl:output
xsl:param
xsl:preserve-space
xsl:strip-space
xsl:template
xsl:variable

Note that the xsl:variable and xsl:param elements can act either as declarations or as instructions. A global variable or parameter is defined using a declaration; a local variable or parameter using an instruction.

If there are xsl:use-package elements, these must come before any other elements. If there are xsl:import elements, these must come after any xsl:use-package elements but before any other elements. Apart from this, the child elements of the xsl:stylesheet element may appear in any order. In most cases, the ordering of these elements does not affect the results of the transformation; however, as described in 6.4 Conflict Resolution for Template Rules, when two template rules with the same priority match the same nodes, there are situations where the order of the template rules will affect which is chosen.

For the meaning of the xsl:use-package element, see 3.6 Packages.

3.8.1 The default-collation Attribute

The default-collation attribute is a standard attribute that may appear on any element in the XSLT namespace, or (as xsl:default-collation) on a literal result element.

The attribute, when it appears on an element E, is used to specify the default collation used by all XPath expressions appearing in attributes or text value templates that have E as an ancestor, unless overridden by another default-collation attribute on an inner element. It also determines the collation used by certain XSLT constructs (such as xsl:key and xsl:for-each-group) within its scope.

The value of the attribute is a whitespace-separated list of collation URIs. If any of these URIs is a relative URI reference, then it is resolved relative to the base URI of the attribute's parent element. If the implementation recognizes one or more of the resulting absolute collation URIs, then it uses the first one that it recognizes as the default collation.

[ERR XTSE0125] It is a static error if the value of an [xsl:]default-collation attribute, after resolving against the base URI, contains no URI that the implementation recognizes as a collation URI.

Note:

The reason the attribute allows a list of collation URIs is that collation URIs will often be meaningful only to one particular XSLT implementation. Stylesheets designed to run with several different implementations can therefore specify several different collation URIs, one for use with each. To avoid the above error condition, it is possible to include as the last collation URI in the list either the Unicode Codepoint Collation or a collation in the UCA family (see 13.4 The Unicode Collation Algorithm) with the parameter fallback=yes.

The [xsl:]default-collation attribute does not affect the collation used by xsl:sort.

In the absence of an [xsl:]default-collation attribute, the default collation may be set by the calling application in an implementation-defined way. The recommended default, unless the user chooses otherwise, is to use the Unicode codepoint collation.

3.8.2 The [xsl:]default-mode Attribute

The default-mode attribute defines the default value for the mode attribute of all xsl:template and xsl:apply-templates elements within its scope. When the mode attribute of these elements is omitted, or when it contains the value #default, then the mode is taken from the [xsl:]default-mode attribute of the innermost ancestor element that has such an attribute. If there is no such element, then the default is the unnamed mode. This is equivalent to specifying #unnamed.

The value must either be an EQName, or the token #unnamed which refers to the unnamed mode. It is not necessary for the referenced mode to be explicitly declared in an xsl:mode declaration.

Note:

This attribute is provided to support an approach to stylesheet modularity in which all the template rules for one mode are collected together into a single stylesheet module. Using this attribute reduces the risk of forgetting to specify the mode in one or more places where it is needed, and it also makes it easier to reuse an existing stylesheet module that does not use modes in an application where modes are needed to avoid conflicts with existing template rules.

3.8.3 User-defined Data Elements

[Definition: In addition to declarations, the xsl:stylesheet element may contain among its children any element not from the XSLT namespace, provided that the expanded QName of the element has a non-null namespace URI. Such elements are referred to as user-defined data elements.]

[ERR XTSE0130] It is a static error if the xsl:stylesheet element has a child element whose name has a null namespace URI.

An implementation may attach an implementation-defined meaning to user-defined data elements that appear in particular namespaces. The set of namespaces that are recognized for such data elements is implementation-defined. The presence of a user-defined data element must not change the behavior of XSLT elements and functions defined in this document; for example, it is not permitted for a user-defined data element to specify that xsl:apply-templates should use different rules to resolve conflicts. The constraints on what user-defined data elements can and cannot do are exactly the same as the constraints on extension attributes, described in 3.3 Extension Attributes. Thus, an implementation is always free to ignore user-defined data elements, and must ignore such data elements without giving an error if it does not recognize the namespace URI.

User-defined data elements can provide, for example,

3.9 Simplified Stylesheet Modules

A simplified syntax is allowed for a stylesheet module that defines only a single template rule for the document node. The stylesheet module may consist of just a literal result element (see 11.1 Literal Result Elements) together with its contents. The literal result element must have an xsl:version attribute (and it must therefore also declare the XSLT namespace). Such a stylesheet module is equivalent to a standard stylesheet module whose xsl:stylesheet element contains a template rule containing the literal result element, minus its xsl:version attribute; the template rule has a match pattern of /.

Example: A Simplified Stylesheet

For example:

<html xsl:version="3.0"
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
      xmlns="http://www.w3.org/1999/xhtml">
  <head>
    <title>Expense Report Summary</title>
  </head>
  <body>
    <p>Total Amount: <xsl:value-of select="expense-report/total"/></p>
  </body>
</html>

has the same meaning as

<xsl:stylesheet version="3.0"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                xmlns="http://www.w3.org/1999/xhtml">
<xsl:template match="/">
<html>
  <head>
    <title>Expense Report Summary</title>
  </head>
  <body>
    <p>Total Amount: <xsl:value-of select="expense-report/total"/></p>
  </body>
</html>
</xsl:template>
</xsl:stylesheet>

Note that it is not possible, using a simplified stylesheet, to request that the serialized output contains a DOCTYPE declaration. This can only be done by using a standard stylesheet module, and using the xsl:output element.

More formally, a simplified stylesheet module is equivalent to the standard stylesheet module that would be generated by applying the following transformation to the simplified stylesheet module, invoking the transformation by calling the named template expand, with the containing literal result element as the context node:

<xsl:stylesheet version="3.0"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:template name="expand">
  <xsl:element name="xsl:stylesheet">
    <xsl:attribute name="version" select="@xsl:version"/>
    <xsl:element name="xsl:template">
      <xsl:attribute name="match" select="'/'"/>
      <xsl:copy-of select="."/>
    </xsl:element>
  </xsl:element>
</xsl:template>  

</xsl:stylesheet>

[ERR XTSE0150] A literal result element that is used as the outermost element of a simplified stylesheet module must have an xsl:version attribute. This indicates the version of XSLT that the stylesheet requires. For this version of XSLT, the value will normally be 3.0 ; the value must be a valid instance of the type xs:decimal as defined in [XML Schema Part 2].

The allowed content of a literal result element when used as a simplified stylesheet is the same as when it occurs within a sequence constructor. Thus, a literal result element used as the document element of a simplified stylesheet cannot contain declarations. Simplified stylesheets therefore cannot use template rules, global variables, stylesheet parameters, stylesheet functions, keys, attribute-sets, or output definitions. In turn this means that the only useful way to initiate the transformation is to supply a document node as the initial context item, to be matched by the implicit match="/" template rule using the unnamed mode.

3.10 Backwards Compatible Processing

[Definition: The effective version of an element in a stylesheet module or package manifest is the decimal value of the [xsl:]version attribute (see 3.5 Standard Attributes) on that element or on the innermost ancestor element that has such an attribute, excluding the version attribute on an xsl:output element.]

[Definition: An element is processed with backwards compatible behavior if its effective version is less than 3.0.]

Specifically:

  • If the effective version is equal to 1.0, then the element is processed with XSLT 1.0 behavior as described in 3.10.1 XSLT 1.0 Compatibility Mode.

  • If the effective version is equal to 2.0, then the element is processed with XSLT 2.0 behavior as described in 3.10.2 XSLT 2.0 Compatibility Mode.

  • If the effective version is any other value less than 3.0, the recommended action is to report a static error; however, processors may recognize such values and process the element in an implementation-defined way.

    Note:

    XSLT 1.0 allowed the version attribute to take any decimal value, and invoked forwards compatible processing for any value other than 1.0. XSLT 2.0 allowed the attribute to take any decimal value, and invoked backwards compatible (i.e. 1.0-compatible) processing for any value less than 2.0. Some stylesheets may therefore be encountered that use values other than 1.0 or 2.0. In particular, the value 1.1 is sometimes encountered, as it was used at one stage in a draft language proposal.

These rules do not apply to the xsl:output element, whose version attribute has an entirely different purpose: it is used to define the version of the output method to be used for serialization.

It is implementation-defined whether a particular XSLT 3.0 implementation supports backwards compatible behavior for any XSLT version earlier than XSLT 3.0.

[ERR XTDE0160] It is a dynamic error if an element has an effective version of V (with V < 3.0) when the implementation does not support backwards compatible behavior for XSLT version V.

Note:

By making use of backwards compatible behavior, it is possible to write the stylesheet in a way that ensures that its results when processed with an XSLT 3.0 processor are identical to the effects of processing the same stylesheet using a processor for an earlier version of XSLT. To assist with transition, some parts of a stylesheet may be processed with backwards compatible behavior enabled, and other parts with this behavior disabled.

All data values manipulated by an XSLT 3.0 processor are defined by the XDM data model, whether or not the relevant expressions use backwards compatible behavior. Because the same data model is used in both cases, expressions are fully composable. The result of evaluating instructions or expressions with backwards compatible behavior is fully defined in the XSLT 3.0 and XPath 3.0 specifications, it is not defined by reference to earlier versions of the XSLT and XPath specifications.

To write a stylesheet that makes use of features that are new in version N, while also working with a processor that only supports XSLT version M (M < N), it is necessary to understand both the rules for backwards compatible behavior in XSLT version N, and the rules for forwards compatible behavior in XSLT version M. If the xsl:stylesheet element specifies version="2.0" or version="3.0", then an XSLT 1.0 processor will ignore XSLT 2.0 and XSLT 3.0 declarations that were not defined in XSLT 1.0, for example xsl:function and xsl:import-schema. If any new XSLT 3.0 instructions are used (for example xsl:evaluate or xsl:stream), or if new XPath 3.0 features are used (for example, new functions, or let expressions), then the stylesheet must provide fallback behavior that relies only on facilities available in the earliest XSLT version supported. The fallback behavior can be invoked by using the xsl:fallback instruction, or by testing the results of the function-available or element-available functions, or by testing the value of the xsl:version property returned by the system-property function.

3.10.1 XSLT 1.0 Compatibility Mode

[Definition: An element in the stylesheet is processed with XSLT 1.0 behavior if its effective version is equal to 1.0.]

In this mode, if any attribute contains an XPath expression, then the expression is evaluated with XPath 1.0 compatibility mode set to true. For details of this mode, see Section 2.1.1 Static Context XP30. Expressions contained in text value templates are always evaluated with XPath 1.0 compatibility mode set to false, since this construct was not available in XSLT 1.0.

Furthermore, in such an expression any function call for which no implementation is available (unless it uses the standard function namespace) is bound to a fallback error function whose effect when evaluated is to raise a dynamic error [see ERR XTDE1425] . The effect is that with backwards compatible behavior enabled, calls on extension functions that are not available in a particular implementation do not cause an error unless the function call is actually evaluated. For further details, see 23.1 Extension Functions.

Note:

This might appear to contradict the specification of XPath 3.0, which states that a static error [XPST0017] is raised when an expression contains a call to a function that is not present (with matching name and arity) in the static context. This apparent contradiction is resolved by specifying that the XSLT processor constructs a static context for the expression in which every possible function name and arity (other than names in the standard function namespace) is present; when no other implementation of the function is available, the function call is bound to a fallback error function whose run-time effect is to raise a dynamic error.

Certain XSLT constructs also produce different results when XSLT 1.0 compatibility mode is enabled. This is described separately for each such construct.

3.10.2 XSLT 2.0 Compatibility Mode

[Definition: An element is processed with XSLT 2.0 behavior if its effective version is equal to 2.0.]

In this specification, no differences are defined for XSLT 2.0 behavior. An XSLT 3.0 processor will therefore produce the same results whether the effective version of an element is set to 2.0 or 3.0.

Note:

An XSLT 2.0 processor, by contrast, will in some cases produce different results in the two cases. For example, if the stylesheet contains an xsl:iterate instruction with an xsl:fallback child, an XSLT 3.0 processor will process the xsl:iterate instruction regardless whether the effective version is 2.0 or 3.0, while an XSLT 2.0 processor will report a static error if the effective version is 2.0, and will take the fallback action if the effective version is 3.0.

3.11 Forwards Compatible Processing

The intent of forwards compatible behavior is to make it possible to write a stylesheet that takes advantage of features introduced in some version of XSLT subsequent to XSLT 3.0, while retaining the ability to execute the stylesheet with an XSLT 3.0 processor using appropriate fallback behavior.

It is always possible to write conditional code to run under different XSLT versions by using the use-when feature described in 3.14 Conditional Element Inclusion. The rules for forwards compatible behavior supplement this mechanism in two ways:

  • certain constructs in the stylesheet that mean nothing to an XSLT 3.0 processor are ignored, rather than being treated as errors.

  • explicit fallback behavior can be defined for instructions defined in a future XSLT release, using the xsl:fallback instruction.

The detailed rules follow.

[Definition: An element is processed with forwards compatible behavior if its effective version is greater than 3.0.]

These rules do not apply to the version attribute of the xsl:output element, which has an entirely different purpose: it is used to define the version of the output method to be used for serialization.

When an element is processed with forwards compatible behavior:

  • if the element is in the XSLT namespace and appears as a child of the xsl:stylesheet element, and XSLT 3.0 does not allow the element to appear as a child of the xsl:stylesheet element, then the element and its content must be ignored.

  • if the element has an attribute that XSLT 3.0 does not allow the element to have, then the attribute must be ignored.

  • if the element is in the XSLT namespace and appears as part of a sequence constructor, and XSLT 3.0 does not allow such elements to appear as part of a sequence constructor, then:

    1. If the element has one or more xsl:fallback children, then no error is reported either statically or dynamically, and the result of evaluating the instruction is the concatenation of the sequences formed by evaluating the sequence constructors within its xsl:fallback children, in document order. Siblings of the xsl:fallback elements are ignored, even if they are valid XSLT 3.0 instructions.

    2. If the element has no xsl:fallback children, then a static error is reported in the same way as if forwards compatible behavior were not enabled.

Example: Forwards Compatible Behavior

For example, an XSLT 3.0 processor will process the following stylesheet without error, although the stylesheet includes elements from the XSLT namespace that are not defined in this specification:

<xsl:stylesheet version="17.0"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:template match="/">
    <xsl:exciting-new-17.0-feature>
      <xsl:fly-to-the-moon/>
      <xsl:fallback>
        <html>
          <head>
            <title>XSLT 17.0 required</title>
          </head>
          <body>
            <p>Sorry, this stylesheet requires XSLT 17.0.</p>
          </body>
        </html>
      </xsl:fallback>
    </xsl:exciting-new-17.0-feature>
  </xsl:template>
</xsl:stylesheet>

Note:

If a stylesheet depends crucially on a declaration introduced by a version of XSLT after 3.0, then the stylesheet can use an xsl:message element with terminate="yes" (see 22.1 Messages) to ensure that implementations that conform to an earlier version of XSLT will not silently ignore the declaration.

Example: Testing the XSLT Version

For example,

<xsl:stylesheet version="18.0"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

  <xsl:important-new-17.0-declaration/>

  <xsl:template match="/">
    <xsl:choose>
      <xsl:when test="number(system-property('xsl:version')) lt 17.0">
        <xsl:message terminate="yes">
          <xsl:text>Sorry, this stylesheet requires XSLT 17.0.</xsl:text>
        </xsl:message>
      </xsl:when>
      <xsl:otherwise>
        ...
      </xsl:otherwise>
    </xsl:choose>
  </xsl:template>
  ...
</xsl:stylesheet>

Note:

The XSLT 1.0 and XSLT 2.0 specifications did not anticipate the introduction of the xsl:package element. An XSLT 1.0 or 2.0 processor encountering this element will report a static error, regardless of the version setting.

This problem can be circumvented by using the simplified package syntax (whereby xsl:use-package appears as a child of xsl:stylesheet, or by writing the stylesheet code in a separate module from the package manifest, and using the separate module as the version of the stylesheet that is presented to a 2.0 processor.

3.12 Combining Stylesheet Modules

XSLT provides two mechanisms to construct a stylesheet from multiple stylesheet modules:

  • an inclusion mechanism that allows stylesheet modules to be combined without changing the semantics of the modules being combined, and

  • an import mechanism that allows stylesheet modules to override each other.

3.12.1 Locating Stylesheet Modules

The include and import mechanisms use two declarations, xsl:include and xsl:import, which are defined in the sections that follow.

These declarations use an href attribute, whose value is a URI reference, to identify the stylesheet module to be included or imported. If the value of this attribute is a relative URI reference, it is resolved as described in 5.9 URI References.

After resolving against the base URI, the way in which the URI reference is used to locate a representation of a stylesheet module, and the way in which the stylesheet module is constructed from that representation, are implementation-defined. In particular, it is implementation-defined which URI schemes are supported, whether fragment identifiers are supported, and what media types are supported. Conventionally, the URI is a reference to a resource containing the stylesheet module as a source XML document, or it may include a fragment identifier that selects an embedded stylesheet module within a source XML document; but the implementation is free to use other mechanisms to locate the stylesheet module identified by the URI reference.

The referenced stylesheet module may be any of the four kinds of stylesheet module: that is, it may be standalone or embedded, and it may be standard or simplified. If it is a simplified stylesheet module then it is transformed into the equivalent standard stylesheet module by applying the transformation described in 3.9 Simplified Stylesheet Modules.

Implementations may choose to accept URI references containing a fragment identifier defined by reference to the XPointer specification (see [XPointer Framework]). Note that if the implementation does not support the use of fragment identifiers in the URI reference, then it will not be possible to include an embedded stylesheet module.

[ERR XTSE0165] It is a static error if the processor is not able to retrieve the resource identified by the URI reference, or if the resource that is retrieved does not contain a stylesheet module.

Note:

It is appropriate to use this error code when the resource cannot be retrieved, or when the retrieved resource is not well formed XML. If the resource contains XML than can be parsed but that violates the rules for stylesheet modules, then a more specific error code may be more appropriate.

3.12.2 Stylesheet Inclusion

<!-- Category: declaration -->
<xsl:include
  href = uri />

A stylesheet module may include another stylesheet module using an xsl:include declaration.

The xsl:include declaration has a required href attribute whose value is a URI reference identifying the stylesheet module to be included. This attribute is used as described in 3.12.1 Locating Stylesheet Modules.

[ERR XTSE0170] An xsl:include element must be a top-level element.

[Definition: A stylesheet level is a collection of stylesheet modules connected using xsl:include declarations: specifically, two stylesheet modules A and B are part of the same stylesheet level if one of them includes the other by means of an xsl:include declaration, or if there is a third stylesheet module C that is in the same stylesheet level as both A and B.]

[Definition: The declarations within a stylesheet level have a total ordering known as declaration order. The order of declarations within a stylesheet level is the same as the document order that would result if each stylesheet module were inserted textually in place of the xsl:include element that references it.] In other respects, however, the effect of xsl:include is not equivalent to the effect that would be obtained by textual inclusion.

[ERR XTSE0180] It is a static error if a stylesheet module directly or indirectly includes itself.

Note:

It is not intrinsically an error for a stylesheet to include the same module more than once. However, doing so can cause errors because of duplicate definitions. Such multiple inclusions are less obvious when they are indirect. For example, if stylesheet B includes stylesheet A, stylesheet C includes stylesheet A, and stylesheet D includes both stylesheet B and stylesheet C, then A will be included indirectly by D twice. If all of B, C and D are used as independent stylesheets, then the error can be avoided by separating everything in B other than the inclusion of A into a separate stylesheet B' and changing B to contain just inclusions of B' and A, similarly for C, and then changing D to include A, B', C'.

3.12.3 Stylesheet Import

<!-- Category: declaration -->
<xsl:import
  href = uri />

A stylesheet module may import another stylesheet module using an xsl:import declaration. Importing a stylesheet module is the same as including it (see 3.12.2 Stylesheet Inclusion) except that template rules and other declarations in the importing module take precedence over template rules and declarations in the imported module; this is described in more detail below.

The xsl:import declaration has a required href attribute whose value is a URI reference identifying the stylesheet module to be included. This attribute is used as described in 3.12.1 Locating Stylesheet Modules.

[ERR XTSE0190] An xsl:import element must be a top-level element.

Example: Using xsl:import

For example,

<xsl:stylesheet version="3.0"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:import href="article.xsl"/>
  <xsl:import href="bigfont.xsl"/>
  <xsl:attribute-set name="note-style">
    <xsl:attribute name="font-style">italic</xsl:attribute>
  </xsl:attribute-set>
</xsl:stylesheet>

[Definition: The stylesheet levels making up a stylesheet are treated as forming an import tree. In the import tree, each stylesheet level has one child for each xsl:import declaration that it contains.] The ordering of the children is the declaration order of the xsl:import declarations within their stylesheet level.

[Definition: A declaration D in the stylesheet is defined to have lower import precedence than another declaration E if the stylesheet level containing D would be visited before the stylesheet level containing E in a post-order traversal of the import tree (that is, a traversal of the import tree in which a stylesheet level is visited after its children). Two declarations within the same stylesheet level have the same import precedence.]

For example, suppose

  • stylesheet module A imports stylesheet modules B and C in that order;

  • stylesheet module B imports stylesheet module D;

  • stylesheet module C imports stylesheet module E.

Then the import tree has the following structure:

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The order of import precedence (lowest first) is D, B, E, C, A.

In general, a declaration with higher import precedence takes precedence over a declaration with lower import precedence. This is defined in detail for each kind of declaration.

[ERR XTSE0210] It is a static error if a stylesheet module directly or indirectly imports itself.

Note:

The case where a stylesheet module with a particular URI is imported several times is not treated specially. The effect is exactly the same as if several stylesheet modules with different URIs but identical content were imported. This might or might not cause an error, depending on the content of the stylesheet module.

3.13 Embedded Stylesheet Modules

An embedded stylesheet module is a stylesheet module whose containing element is not the outermost element of the containing XML document. Both standard stylesheet modules and simplified stylesheet modules may be embedded in this way.

Two situations where embedded stylesheets may be useful are:

  • The stylesheet may be embedded in the source document to be transformed.

  • The stylesheet may be embedded in an XML document that describes a sequence of processing of which the XSLT transformation forms just one part.

The xsl:stylesheet element may have an id attribute to facilitate reference to the stylesheet module within the containing document.

Note:

In order for such an attribute value to be used as a fragment identifier in a URI, the XDM attribute node must generally have the is-id property: see Section 5.5 is-id Accessor DM30. This property will typically be set if the attribute is defined in a DTD as being of type ID, or if is defined in a schema as being of type xs:ID. It is also necessary that the media type of the containing document should support the use of ID values as fragment identifiers. Such support is widespread in existing products, and is endorsed in respect of the media type application/xml by [XPointer Framework].

An alternative, if the implementation supports it, is to use an xml:id attribute. XSLT allows this attribute (like other namespaced attributes) to appear on any XSLT element.

Example: The xml-stylesheet Processing Instruction

The following example shows how the xml-stylesheet processing instruction (see [XML Stylesheet]) can be used to allow a source document to contain its own stylesheet. The URI reference uses a fragment identifier to locate the xsl:stylesheet element:

<?xml-stylesheet type="application/xslt+xml" href="#style1"?>
<!DOCTYPE doc SYSTEM "doc.dtd">
<doc>
  <head>
    <xsl:stylesheet id="style1"
                    version="3.0"
                    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                    xmlns:fo="http://www.w3.org/1999/XSL/Format">
    <xsl:import href="doc.xsl"/>
    <xsl:template match="id('foo')">
      <fo:block font-weight="bold"><xsl:apply-templates/></fo:block>
    </xsl:template>
    <xsl:template match="xsl:stylesheet">
      <!-- ignore -->
    </xsl:template>
    </xsl:stylesheet>
  </head>
  <body>
    <para id="foo">
    ...
    </para>
  </body>
</doc>

Note:

A stylesheet module that is embedded in the document to which it is to be applied typically needs to contain a template rule that specifies that xsl:stylesheet elements are to be ignored.

Note:

The above example uses the pseudo-attribute type="application/xslt+xml" in the xml-stylesheet processing instruction to denote an XSLT stylesheet. This is the officially registered media type for XSLT: see 3.4 XSLT Media Type. However, browsers developed before this media type was registered are more likely to accept the unofficial designation type="text/xsl".

Note:

Support for the xml-stylesheet processing instruction is not required for conformance with this Recommendation. Implementations are not constrained in the mechanisms they use to identify a stylesheet when a transformation is initiated: see 2.3 Initiating a Transformation.

3.14 Conditional Element Inclusion

Any element in the XSLT namespace may have a use-when attribute whose value is an XPath expression that can be evaluated statically. If the attribute is present and the effective boolean valueXP30 of the expression is false, then the element, together with all the nodes having that element as an ancestor, is effectively excluded from the stylesheet module. When a node is effectively excluded from a stylesheet module the stylesheet module has the same effect as if the node were not there. Among other things this means that no static or dynamic errors will be reported in respect of the element and its contents, other than errors in the use-when attribute itself.

Note:

This does not apply to XML parsing or validation errors, which will be reported in the usual way. It also does not apply to attributes that are necessarily processed before [xsl:]use-when, examples being xml:space and [xsl:]xpath-default-namespace.

A literal result element, or any other element within a stylesheet module that is not in the XSLT namespace, may similarly carry an xsl:use-when attribute.

If the xsl:stylesheet or xsl:transform element itself is effectively excluded, the effect is to exclude all the children of the xsl:stylesheet or xsl:transform element, but not the xsl:stylesheet or xsl:transform element or its attributes.

Note:

This allows all the declarations that depend on the same condition to be included in one stylesheet module, and for their inclusion or exclusion to be controlled by a single use-when attribute at the level of the module.

Conditional element exclusion happens after stripping of whitespace text nodes from the stylesheet, as described in 4.2 Stripping Whitespace from the Stylesheet.

The XPath expression used as the value of the xsl:use-when attribute follows the rules for static expressions.

The use of [xsl:]use-when is illustrated in the following examples.

Example: Using Conditional Exclusion to Achieve Portability

This example demonstrates the use of the use-when attribute to achieve portability of a stylesheet across schema-aware and non-schema-aware processors.

<xsl:import-schema schema-location="http://example.com/schema"
              use-when="system-property('xsl:is-schema-aware')='yes'"/>

<xsl:template match="/" 
              use-when="system-property('xsl:is-schema-aware')='yes'" 
              priority="2">
  <xsl:result-document validation="strict">
    <xsl:apply-templates/>
  </xsl:result-document>
</xsl:template>

<xsl:template match="/">
  <xsl:apply-templates/>
</xsl:template>

The effect of these declarations is that a non-schema-aware processor ignores the xsl:import-schema declaration and the first template rule, and therefore generates no errors in respect of the schema-related constructs in these declarations.

 

Example: Including Variant Stylesheet Modules

This example includes different stylesheet modules depending on which XSLT processor is in use.

<xsl:include href="module-A.xsl" 
     use-when="system-property('xsl:vendor')='vendor-A'"/>
<xsl:include href="module-B.xsl" 
     use-when="system-property('xsl:vendor')='vendor-B'"/>

3.15 Built-in Types

Every XSLT 3.0 processor includes the following named type definitions in the in-scope schema components:

  • All built-in types defined in [XML Schema Part 2], including xs:anyType and xs:anySimpleType.

  • The following types defined in [XPath 3.0]: xs:yearMonthDuration, xs:dayTimeDuration, xs:anyAtomicType, xs:untyped, and xs:untypedAtomic.

XSLT 3.0 processors may optionally include types defined in XSD 1.1 (see [XML Schema]). XSD 1.1 adopts the types xs:yearMonthDuration, xs:dayTimeDuration, and xs:anyAtomicType previously defined in XPath 2.0, and adds one new type: xs:dateTimeStamp. XSD 1.1 also allows implementors to define additional primitive types, and XSLT 3.0 permits such types to be supported by an XSLT processor.

A schema-aware XSLT processor additionally supports:

Note:

The names that are imported from the XML Schema namespace do not include all the names of top-level types defined in either the Schema for Schema Documents or the Schema for Schema Documents (Datatypes). The Schema for Schema Documents, as well as defining built-in types such as xs:integer and xs:double, also defines types that are intended for use only within that schema, such as xs:derivationControl. A stylesheet that is designed to process XML Schema documents as its input or output may import the Schema for Schema Documents.

An implementation may define mechanisms that allow additional schema components to be added to the in-scope schema components for the stylesheet. For example, the mechanisms used to define extension functions (see 23.1 Extension Functions) may also be used to import the types used in the interface to such functions.

These schema components are the only ones that may be referenced in XPath expressions within the stylesheet, or in the [xsl:]type and as attributes of those elements that permit these attributes.

3.16 Importing Schema Components

Note:

The facilities described in this section are not available with a basic XSLT processor. They require a schema-aware XSLT processor, as described in 26 Conformance.

<!-- Category: declaration -->
<xsl:import-schema
  namespace? = uri
  schema-location? = uri >
  <!-- Content: xs:schema? -->
</xsl:import-schema>

The xsl:import-schema declaration is used to identify schema components (that is, top-level type definitions and top-level element and attribute declarations) that need to be available statically, that is, before any source document is available. Names of such components used statically within the stylesheet must refer to an in-scope schema component, which means they must either be built-in types as defined in 3.15 Built-in Types, or they must be imported using an xsl:import-schema declaration.

The xsl:import-schema declaration identifies a namespace containing the names of the components to be imported (or indicates that components whose names are in no namespace are to be imported). The effect is that the names of top-level element and attribute declarations and type definitions from this namespace (or non-namespace) become available for use within XPath expressions in the package, and within other stylesheet constructs such as the type and as attributes of various XSLT elements.

The same schema components are available in all stylesheet modules within the declaring package; importing components in one stylesheet module makes them available throughout the package.

The schema components imported into different packages within a stylesheet must be consistent. Specifically, it is not permitted to use the same name in the same XSD symbol space to refer to different schema components within different packages; and the union of the schema components imported into the packages of a stylesheet must constitute a valid schema (as well as the set of schema components imported into each package forming a valid schema in its own right).

The namespace and schema-location attributes are both optional.

If the xsl:import-schema element contains an xs:schema element, then the schema-location attribute must be absent, and one of the following must be true:

  • the namespace attribute of the xsl:import-schema element and the targetNamespace attribute of the xs:schema element are both absent (indicating a no-namespace schema), or

  • the namespace attribute of the xsl:import-schema element and the targetNamespace attribute of the xs:schema element are both present and both have the same value, or

  • the namespace attribute of the xsl:import-schema element is absent and the targetNamespace attribute of the xs:schema element is present, in which case the target namespace is as given on the xs:schema element.

[ERR XTSE0215] It is a static error if an xsl:import-schema element that contains an xs:schema element has a schema-location attribute, or if it has a namespace attribute that conflicts with the target namespace of the contained schema.

If two xsl:import-schema declarations specify the same namespace, or if both specify no namespace, then only the one with highest import precedence is used. If this leaves more than one, then all the declarations at the highest import precedence are used (which may cause conflicts, as described below).

After discarding any xsl:import-schema declarations under the above rule, the effect of the remaining xsl:import-schema declarations is defined in terms of a hypothetical document called the synthetic schema document, which is constructed as follows. The synthetic schema document defines an arbitrary target namespace that is different from any namespace actually used by the application, and it contains xs:import elements corresponding one-for-one with the xsl:import-schema declarations in the stylesheet, with the following correspondence:

  • The namespace attribute of the xs:import element is copied from the namespace attribute of the xsl:import-schema declaration if it is explicitly present, or is implied by the targetNamespace attribute of a contained xs:schema element, and is absent if it is absent.

  • The schemaLocation attribute of the xs:import element is copied from the schema-location attribute of the xsl:import-schema declaration if present, and is absent if it is absent. If there is a contained xs:schema element, the effective value of the schemaLocation attribute is a URI referencing a document containing a copy of the xs:schema element.

  • The base URI of the xs:import element is the same as the base URI of the xsl:import-schema declaration.

The schema components included in the in-scope schema components (that is, the components whose names are available for use within the stylesheet) are the top-level element and attribute declarations and type definitions that are available for reference within the synthetic schema document. See [XML Schema Part 1] (section 4.2.3, References to schema components across namespaces).

[ERR XTSE0220] It is a static error if the synthetic schema document does not satisfy the constraints described in [XML Schema Part 1] (section 5.1, Errors in Schema Construction and Structure). This includes, without loss of generality, conflicts such as multiple definitions of the same name.

Note:

The synthetic schema document does not need to be constructed by a real implementation. It is purely a mechanism for defining the semantics of xsl:import-schema in terms of rules that already exist within the XML Schema specification. In particular, it implicitly defines the rules that determine whether the set of xsl:import-schema declarations are mutually consistent.

These rules do not cause names to be imported transitively. The fact that a name is available for reference within a schema document A does not of itself make the name available for reference in a stylesheet that imports the target namespace of schema document A. (See [XML Schema Part 1] section 3.15.3, Constraints on XML Representations of Schemas.) The stylesheet must import all the namespaces containing names that it actually references.

The namespace attribute indicates that a schema for the given namespace is required by the stylesheet. This information may be enough on its own to enable an implementation to locate the required schema components. The namespace attribute may be omitted to indicate that a schema for names in no namespace is being imported. The zero-length string is not a valid namespace URI, and is therefore not a valid value for the namespace attribute.

The schema-location attribute is a URI Reference that gives a hint indicating where a schema document or other resource containing the required definitions may be found. It is likely that a schema-aware XSLT processor will be able to process a schema document found at this location.

The XML Schema specification gives implementations flexibility in how to handle multiple imports for the same namespace. Multiple imports do not cause errors if the definitions do not conflict.

A consequence of these rules is that it is not intrinsically an error if no schema document can be located for a namespace identified in an xsl:import-schema declaration. This will cause an error only if it results in the stylesheet containing references to names that have not been imported.

An inline schema document (using an xs:schema element as a child of the xsl:import-schema element) has the same status as an external schema document, in the sense that it acts as a hint for a source of schema components in the relevant namespace. To ensure that the inline schema document is always used, it is advisable to use a target namespace that is unique to this schema document.

The use of a namespace in an xsl:import-schema declaration does not by itself associate any namespace prefix with the namespace. If names from the namespace are used within the stylesheet module then a namespace declaration must be included in the stylesheet module, in the usual way.

Example: An Inline Schema Document

The following example shows an inline schema document. This declares a simple type local:yes-no, which the stylesheet then uses in the declaration of a variable.

The example assumes the namespace declaration xmlns:local="http://example.com/ns/yes-no"

<xsl:import-schema>
  <xs:schema targetNamespace="http://example.com/ns/yes-no"
             xmlns:xs="http://www.w3.org/2001/XMLSchema"
             xmlns:local="http://example.com/ns/yes-no">
    <xs:simpleType name="yes-no">
      <xs:restriction base="xs:string">
        <xs:enumeration value="yes"/>
        <xs:enumeration value="no"/>
      </xs:restriction>
    </xs:simpleType>
  </xs:schema>
</xsl:import-schema>

<xsl:variable name="condition" select="local:yes-no('yes')" 
                               as="local:yes-no"/>

4 Data Model

The data model used by XSLT is the XPath 3.0 and XQuery 3.0 data model (XDM), as defined in [Data Model]. XSLT operates on source, result and stylesheet documents using the same data model.

This section elaborates on some particular features of XDM as it is used by XSLT:

The rules in 4.2 Stripping Whitespace from the Stylesheet and 4.4 Stripping Whitespace from a Source Tree make use of the concept of a whitespace text node.

[Definition: A whitespace text node is a text node whose content consists entirely of whitespace characters (that is, #x09, #x0A, #x0D, or #x20).]

Note:

Features of a source XML document that are not represented in the XDM tree will have no effect on the operation of an XSLT stylesheet. Examples of such features are entity references, CDATA sections, character references, whitespace within element tags, and the choice of single or double quotes around attribute values.

4.1 XML Versions

The XDM data model defined in [Data Model] is capable of representing either an XML 1.0 document (conforming to [XML 1.0] and [Namespaces in XML]) or an XML 1.1 document (conforming to [XML 1.1] and [Namespaces in XML 1.1]), and it makes no distinction between the two. In principle, therefore, XSLT 3.0 can be used with either of these XML versions.

Construction of the XDM tree is outside the scope of this specification, so XSLT 3.0 places no formal requirements on an XSLT processor to accept input from either XML 1.0 documents or XML 1.1 documents or both. This specification does define a serialization capability (see 25 Serialization), though from a conformance point of view it is an optional feature. Although facilities are described for serializing the XDM tree as either XML 1.0 or XML 1.1 (and controlling the choice), there is again no formal requirement on an XSLT processor to support either or both of these XML versions as serialization targets.

Because the XDM tree is the same whether the original document was XML 1.0 or XML 1.1, the semantics of XSLT processing do not depend on the version of XML used by the original document. There is no reason in principle why all the input and output documents used in a single transformation must conform to the same version of XML.

Some of the syntactic constructs in XSLT 3.0 and XPath 3.0, for example the productions CharXML and NCNameNames, are defined by reference to the XML and XML Namespaces specifications. There are slight variations between the XML 1.0 and XML 1.1 versions of these productions (and, indeed, between different editions of XML 1.0). Implementations may support any version; it is recommended that an XSLT 3.0 processor that implements the 1.1 versions should also provide a mode that supports the 1.0 versions. It is thus implementation-defined whether the XSLT processor supports XML 1.0 with XML Namespaces 1.0, or XML 1.1 with XML Namespaces 1.1, or supports both versions at user option.

Note:

The specification referenced as [Namespaces in XML] was actually published without a version number.

The current version of [XML Schema Part 2] (that is, XSD 1.0) does not reference the XML 1.1 specifications. This means that datatypes such as xs:NCName and xs:ID are constrained by the XML 1.0 rules, and do not allow the full range of values permitted by XML 1.1. This situation will not be resolved until a new version of [XML Schema Part 2] becomes available; in the meantime, it is recommended that implementers wishing to support XML 1.1 should consult [XML Schema 1.0 and XML 1.1] for guidance. An XSLT 3.0 processor that supports XML 1.1 should implement the rules in later versions of [XML Schema Part 2] as they become available.

4.2 Stripping Whitespace from the Stylesheet

The tree representing the stylesheet is preprocessed as follows:

  1. All comments and processing instructions are removed.

  2. Any text nodes that are now adjacent to each other are merged.

  3. Any whitespace text node that satisfies both the following conditions is removed from the tree:

    • The parent of the text node is not an xsl:text element

    • The text node does not have an ancestor element that has an xml:space attribute with a value of preserve, unless there is a closer ancestor element having an xml:space attribute with a value of default.

  4. Any whitespace text node whose parent is one of the following elements is removed from the tree, regardless of any xml:space attributes:

    xsl:accumulator
    xsl:analyze-string
    xsl:apply-imports
    xsl:apply-templates
    xsl:attribute-set
    xsl:call-template
    xsl:character-map
    xsl:choose
    xsl:evaluate
    xsl:fork
    xsl:merge
    xsl:merge-source
    xsl:mode
    xsl:next-iteration
    xsl:next-match
    xsl:override
    xsl:package
    xsl:stylesheet
    xsl:transform
    xsl:use-package

  5. Any whitespace text node whose immediate following-sibling node is an xsl:param or xsl:sort element is removed from the tree, regardless of any xml:space attributes.

  6. Any whitespace text node whose immediate preceding-sibling node is an xsl:catch or xsl:on-completion element is removed from the tree, regardless of any xml:space attributes.

[ERR XTSE0260] Within an XSLT element that is required to be empty, any content other than comments or processing instructions, including any whitespace text node preserved using the xml:space="preserve" attribute, is a static error.

Note:

Using xml:space="preserve" in parts of the stylesheet that contain sequence constructors will cause whitespace text nodes in that part of the stylesheet to be copied to the result of the sequence constructor. When the result of the sequence constructor is used to form the content of an element, this can cause errors if such text nodes are followed by attribute nodes generated using xsl:attribute.

Note:

If an xml:space attribute is specified on a literal result element, it will be copied to the result tree in the same way as any other attribute.

4.3 Stripping Type Annotations from a Source Tree

[Definition: The term type annotation is used in this specification to refer to the value returned by the dm:type-name accessor of a node: see Section 5.14 type-name Accessor DM30.]

There is sometimes a requirement to write stylesheets that produce the same results whether or not the source documents have been validated against a schema. To achieve this, an option is provided to remove any type annotations on element and attribute nodes in a source tree, replacing them with an annotation of xs:untyped in the case of element nodes, and xs:untypedAtomic in the case of attribute nodes.

Such stripping of type annotations can be requested by specifying input-type-annotations="strip" on the xsl:package element. This attribute has three permitted values: strip, preserve, and unspecified. The default value is unspecified.

The input-type-annotations attribute may also be specified on the xsl:stylesheet element; if it is specified at this level then it must be consistent for all stylesheet modules within the same package.

[ERR XTSE0265] It is a static error if there is a stylesheet module in a package that specifies input-type-annotations="strip" and another stylesheet module that specifies input-type-annotations="preserve", or if a stylesheet module specifies the value strip or preserve and the same value is not specified on the xsl:package element of the containing package.

The source trees to which this applies are the same as those affected by xsl:strip-space and xsl:preserve-space: see 4.4 Stripping Whitespace from a Source Tree. As with whitespace stripping, the rules for stripping of type annotations may vary from one package to another, and have the effect of modifying the mapping from URIs to document nodes defined in the XPath dynamic context; this means that two calls to the docFO30 function (for example) supplying the same URI may produce different document nodes if the calls appear in different packages.

When type annotations are stripped, the following changes are made to the source tree:

  • The type annotation of every element node is changed to xs:untyped

  • The type annotation of every attribute node is changed to xs:untypedAtomic

  • The typed value of every element and attribute node is set to be the same as its string value, as an instance of xs:untypedAtomic.

  • The is-nilled property of every element node is set to false.

The values of the is-id and is-idrefs properties are not changed.

Note:

Stripping type annotations does not necessarily return the document to the state it would be in had validation not taken place. In particular, any defaulted elements and attributes that were added to the tree by the validation process will still be present , and elements and attributes validated as IDs will still be accessible using the idFO30 function.

4.4 Stripping Whitespace from a Source Tree

A source tree supplied as input to the transformation process may contain whitespace text nodes that are of no interest, and that do not need to be retained by the transformation. Conceptually, an XSLT processor makes a copy of the source tree from which unwanted whitespace text nodes have been removed. This process is referred to as whitespace stripping.

For the purposes of this section, the term source tree means the document containing the initial context item if it is a node, any document returned by the functions document, docFO30, or collectionFO30, and any document read using xsl:stream. It does not include documents passed as the values of stylesheet parameters or parameters of the initial template or function, nor values returned from extension functions.

Each source tree is associated with a package: the relevant package for the initial context item is the top-level package; the relevant package for a call on document, docFO30, or collectionFO30; is the package in which that call appears; and the relevant package for evaluation of xsl:stream is the package in which that instruction appears.

The stripping process takes as input a set of element names whose child whitespace text nodes are to be preserved. The way in which this set of element names is established using the xsl:strip-space and xsl:preserve-space declarations is described later in this section.

Formally, the stripping process modifies the mapping from URIs to document nodes defined in the XPath dynamic context. This mapping can therefore vary from one package to another. The mapping that applies to a particular call on document, docFO30, or collectionFO30, or a particular evaluation of xsl:stream, is affected by the xsl:strip-space and xsl:preserve-space declarations within the package in which that construct appears. This means that two calls on the docFO30 function (for example) may return different nodes if the calls appear in different packages.

A whitespace text node is preserved if either of the following apply:

  • The element name of the parent of the text node is in the set of whitespace-preserving element names.

  • An ancestor element of the text node has an xml:space attribute with a value of preserve, and no closer ancestor element has xml:space with a value of default.

Otherwise, the whitespace text node is stripped.

The xml:space attributes are not removed from the tree.

<!-- Category: declaration -->
<xsl:strip-space
  elements = tokens />

<!-- Category: declaration -->
<xsl:preserve-space
  elements = tokens />

The set of whitespace-preserving element names is specified by xsl:strip-space and xsl:preserve-space declarations. Whether an element name is included in the set of whitespace-preserving names is determined by the best match among all the xsl:strip-space or xsl:preserve-space declarations: it is included if and only if there is no match or the best match is an xsl:preserve-space element. The xsl:strip-space and xsl:preserve-space elements each have an elements attribute whose value is a whitespace-separated list of NameTestsXP30; an element name matches an xsl:strip-space or xsl:preserve-space element if it matches one of the NameTestsXP30. An element matches a NameTestXP30 if and only if the NameTestXP30 would be true for the element as an XPath node test.

The effect of xsl:strip-space and xsl:preserve-space is local to the package in which they appear. Declarations within a library package only affect the handling of documents loaded using a call on the document, docFO30, or collectionFO30 functions or an evaluation of an xsl:stream instruction appearing lexically within the same package. Declarations within the top-level package also affect the processing of the main input document.

[ERR XTSE0270] It is a static error if within any package the same NameTestXP30 appears in both an xsl:strip-space and an xsl:preserve-space declaration if both have the same import precedence. Two NameTests are considered the same if they match the same set of names (which can be determined by comparing them after expanding namespace prefixes to URIs).

Otherwise, when more than one xsl:strip-space and xsl:preserve-space element within the relevant package matches, the best matching element is determined by the best matching NameTestXP30. The rules are similar to those for template rules:

  • First, any match with lower import precedence than another match is ignored.

  • Next, any match that has a lower default priority than the default priority of another match is ignored.

  • If several matches have the same default priority (which can only happen if one of the NameTests takes the form *:local and the other takes the form prefix:*), then the declaration that appears last in declaration order is used.

If an element in a source document has a type annotation that is a simple type or a complex type with simple content, then any whitespace text nodes among its children are preserved, regardless of any xsl:strip-space declarations. The reason for this is that stripping a whitespace text node from an element with simple content could make the element invalid: for example, it could cause the minLength facet to be violated.

Stripping of type annotations happens before stripping of whitespace text nodes, so this situation will not occur if input-type-annotations="strip" is specified.

Note:

In [Data Model], processes are described for constructing an XDM tree from an Infoset or from a PSVI. Those processes deal with whitespace according to their own rules, and the provisions in this section apply to the resulting tree. In practice this means that elements that are defined in a DTD or a Schema to contain element-only content will have whitespace text nodes stripped, regardless of the xsl:strip-space and xsl:preserve-space declarations in the stylesheet.

However, source trees are not necessarily constructed using those processes; indeed, they are not necessarily constructed by parsing XML documents. Nothing in the XSLT specification constrains how the source tree is constructed, or what happens to whitespace text nodes during its construction. The provisions in this section relate only to whitespace text nodes that are present in the tree supplied as input to the XSLT processor. The XSLT processor cannot preserve whitespace text nodes unless they were actually present in the supplied tree.

4.5 Attribute Types and DTD Validation

The mapping from the Infoset to the XDM data model, described in [Data Model], does not retain attribute types. This means, for example, that an attribute described in the DTD as having attribute type NMTOKENS will be annotated in the XDM tree as xs:untypedAtomic rather than xs:NMTOKENS, and its typed value will consist of a single xs:untypedAtomic value rather than a sequence of xs:NMTOKEN values.

Attributes with a DTD-derived type of ID, IDREF, or IDREFS will be marked in the XDM tree as having the is-id or is-idrefs properties. It is these properties, rather than any type annotation, that are examined by the functions idFO30 and idrefFO30 described in [Functions and Operators].

4.6 Data Model for Streaming

The data model for nodes in a document that is being streamed is no different from the standard XDM data model, in that it contains the same objects (nodes) with the same properties and relationships. The facilities for streaming do not change the data model; instead they impose rules that limit the ability of stylesheets to navigate the data model.

A useful way to visualize streaming is to suppose that at any point in time, there is a current position in the streamed input document which may be the start or end of the document, the start or end tag of an element, or a text, comment, or processing instruction node. From this position, the stylesheet has access to the following information:

  • Properties intrinsic to the node, such as its name, its base URI, its type annotation, and its is-id and is-idref properties.

  • The ancestors of the node (but navigation downwards from the ancestors is not permitted).

  • The attributes of the node, and the attributes of its ancestors. For each such attribute, all the properties of the node including its string value and typed value are available, but there are limitations that restrict navigation from the attribute node to other nodes in the document.

  • The in-scope namespace bindings of the node.

  • In the case of attributes, text nodes, comments, and processing instructions, the string value and typed value of the node.

  • Summary data about the preceding siblings of the node, and of each of its ancestor nodes: specifically, for each distinct combination of node kind, node name, and type annotation, a count of the number of preceding siblings that have that combination of properties. This information allows patterns such as match="para[1]" to be used, and it permits some limited use of the xsl:number instruction.

The children and other descendants of a node are not accessible except as a by-product of changing the current position in the document. The same applies to properties of an element or document node that require examination of the node's descendants, that is, the string value and typed value. This is enforced by means of a rule that only one expression requiring downward navigation from a node is permitted.

There is an assumption that information about unparsed entities is available at all times during the processing of a document. This has two implications: firstly, the processor may need to read ahead at the start of the document to determine this information so that it is available while processing the document root node; and secondly, the information then needs to be retained for the duration of the processing.

Expressions such as (/) instance of document-node(element(invoice)) also require look-ahead as far as the start-tag of the first element.

A streaming processor is required to read only as much of the source document as is needed to generate correct stylesheet output. It is not required to read the full source document merely in order to satisfy the requirement imposed by the XML Recommendation that an XML Processor must report violations of well-formedness in the input.

More detailed rules are defined in 19 Streamability.

4.7 Limits

The XDM data model (see [Data Model]) leaves it to the host language to define limits. This section describes the limits that apply to XSLT.

Limits on some primitive datatypes are defined in [XML Schema Part 2]. Other limits, listed below, are implementation-defined. Note that this does not necessarily mean that each limit must be a simple constant: it may vary depending on environmental factors such as available resources.

The following limits are implementation-defined:

  1. For the xs:decimal type, the maximum number of decimal digits (the totalDigits facet). This must be at least 18 digits. (Note, however, that support for the full value range of xs:unsignedLong requires 20 digits.)

  2. For the types xs:date, xs:time, xs:dateTime, xs:gYear, and xs:gYearMonth: the range of values of the year component, which must be at least +0001 to +9999; and the maximum number of fractional second digits, which must be at least 3.

  3. For the xs:duration type: the maximum absolute values of the years, months, days, hours, minutes, and seconds components.

  4. For the xs:yearMonthDuration type: the maximum absolute value, expressed as an integer number of months.

  5. For the xs:dayTimeDuration type: the maximum absolute value, expressed as a decimal number of seconds.

  6. For the types xs:string, xs:hexBinary, xs:base64Binary, xs:QName, xs:anyURI, xs:NOTATION, and types derived from them: the maximum length of the value.

  7. For sequences, the maximum number of items in a sequence.

4.8 Disable Output Escaping

For backwards compatibility reasons, XSLT 3.0 continues to support the disable-output-escaping feature introduced in XSLT 1.0. This is an optional feature and implementations are not required to support it. A new facility, that of named character maps (see 25.1 Character Maps) was introduced in XSLT 2.0. It provides similar capabilities to disable-output-escaping, but without distorting the data model.

If an implementation supports the disable-output-escaping attribute of xsl:text and xsl:value-of, (see 25.2 Disabling Output Escaping), then the data model for trees constructed by the processor is augmented with a boolean value representing the value of this property. This boolean value, however, can be set only within a final result tree that is being passed to the serializer.

Conceptually, each character in a text node on such a result tree has a boolean property indicating whether the serializer is to disable the normal rules for escaping of special characters (for example, outputting of & as &amp;) in respect of this character.

Note:

In practice, the nodes in a final result tree will often be streamed directly from the XSLT processor to the serializer. In such an implementation, disable-output-escaping can be viewed not so much a property stored with nodes in the tree, but rather as additional information passed across the interface between the XSLT processor and the serializer.

5 Features of the XSLT Language

5.1 Qualified Names

The name of a stylesheet-defined object, specifically a named template, a mode, an attribute set, a key, a decimal-format, a variable or parameter, a stylesheet function, a named output definition, or a character map is a qualified name: that is, it consists of a local name and an optional namespace URI.

In most cases where such names are written in a stylesheet, the syntax for expressing the name is given by the production EQNameXP30 in the XPath specification. In practice, this means that three forms are permitted:

  • A simple NCName appearing on its own (without any prefix). This represents the local name of the object. The interpretation of unprefixed names is described below.

  • A lexical QName written in the form NCName ":" NCName where the first part is a namespace prefix and the second part is the local name. The namespace part of the object's name is then derived from the prefix by examining the in-scope namespace bindings of the element node in the stylesheet where the name appears.

  • A URIQualifiedNameXP30 in the form "Q{" URI? "}" NCName where the two parts of the name, that is the namespace part and the local part, both appear explicitly. If the URI part is omitted (for example Q{}local), the resulting expanded QName is a QName whose namespace part is absent.

Note:

There are a few places where the third form, a URIQualifiedName, is not permitted. These include the name attribute of xsl:element and xsl:attribute (which have a separate namespace attribute for the purpose), and constructs defined by other specifications. For example, names appearing within an embedded xs:schema element must follow the XSD rules.

[Definition: An expanded QName is a value in the value space of the xs:QName datatype as defined in the XDM data model (see [Data Model]): that is, a triple containing namespace prefix (optional), namespace URI (optional), and local name. Two expanded QNames are equal if the namespace URIs are the same (or both absent) and the local names are the same. The prefix plays no part in the comparison, but is used only if the expanded QName needs to be converted back to a string.]

[Definition: An EQName is a string representing a expanded QName where the string, after removing leading and trailing whitespace, is in the form defined by the EQNameXP30 production in the XPath specification.]

[Definition: A lexical QName is a string representing a expanded QName where the string, after removing leading and trailing whitespace, is within the lexical space of the xs:QName datatype as defined in XML Schema (see [XML Schema Part 2]): that is, a local name optionally preceded by a namespace prefix and a colon.]

Note that every lexical QName is an EQName, but the converse is not true.

The following rules are used when interpreting a lexical QName:

  1. [Definition: A string in the form of a lexical QName may occur as the value of an attribute node in a stylesheet module, or within an XPath expression contained in an attribute or text node within a stylesheet module, or as the result of evaluating an XPath expression contained in such a node. The element containing this attribute or text node is referred to as the defining element of the lexical QName.]

  2. If the lexical QName has a prefix, then the prefix is expanded into a URI reference using the namespace declarations in effect on its defining element. The expanded QName consisting of the local part of the name and the possibly null URI reference is used as the name of the object. The default namespace of the defining element (see Section 6.2 Element Nodes DM30) is not used for unprefixed names.

    [ERR XTSE0280] In the case of a prefixed lexical QName used as the value (or as part of the value) of an attribute in the stylesheet, or appearing within an XPath expression in the stylesheet, it is a static error if the defining element has no namespace node whose name matches the prefix of the lexical QName.

    [ERR XTDE0290] Where the result of evaluating an XPath expression (or an attribute value template) is required to be a lexical QName, or if it is permitted to be a lexical QName and the actual value takes the form of a lexical QName, then unless otherwise specified it is a dynamic error if the value has a prefix and the defining element has no namespace node whose name matches that prefix. This error may be signaled as a static error if the value of the expression can be determined statically.

  3. If the lexical QName has no prefix, then:

    1. In the case of an unprefixed QName used as a NameTest within an XPath expression (see 5.3 Expressions) , and in certain other contexts, the namespace to be used in expanding the QName may be specified by means of the [xsl:]xpath-default-namespace attribute, as specified in 5.2 Unprefixed Lexical QNames in Expressions and Patterns.

    2. If the name is in one of the following categories, then the default namespace of the defining element is used:

      1. Where a QName is used to define the name of an element being constructed. This applies both to cases where the name is known statically (that is, the name of a literal result element) and to cases where it is computed dynamically (the value of the name attribute of the xsl:element instruction).

      2. The default namespace is used when expanding the first argument of the function element-available.

      3. The default namespace applies to any unqualified element names appearing in the cdata-section-elements attribute of xsl:output or xsl:result-document

    3. In all other cases, a lexical QName with no prefix represents an expanded QName in no namespace (that is, an xs:QName value in which both the prefix and the namespace URI are absent).

5.2 Unprefixed Lexical QNames in Expressions and Patterns

The attribute [xsl:]xpath-default-namespace (see 3.5 Standard Attributes) may be used on an element in the stylesheet to define the namespace that will be used for an unprefixed element name or type name within an XPath expression, and in certain other contexts listed below.

The value of the attribute is the namespace URI to be used.

For any element in the stylesheet, this attribute has an effective value, which is the value of the [xsl:]xpath-default-namespace on that element or on the innermost containing element that specifies such an attribute, or the zero-length string if no containing element specifies such an attribute.

For any element in the stylesheet, the effective value of this attribute determines the value of the default namespace for element and type names in the static context of any XPath expression contained in an attribute or text node of that element (including XPath expressions in attribute value templates and text value templates). The effect of this is specified in [XPath 3.0]; in summary, it determines the namespace used for any unprefixed type name in the SequenceType production, and for any element name appearing in a path expression or in the SequenceType production.

The effective value of this attribute similarly applies to any of the following constructs appearing within its scope:

The [xsl:]xpath-default-namespace attribute must be in the XSLT namespace if and only if its parent element is not in the XSLT namespace.

If the effective value of the attribute is a zero-length string, which will be the case if it is explicitly set to a zero-length string or if it is not specified at all, then an unprefixed element name or type name refers to a name that is in no namespace. The default namespace of the parent element (see Section 6.2 Element Nodes DM30) is not used.

The attribute does not affect other names, for example function names, variable names, or template names, or strings that are interpreted as lexical QNames during stylesheet evaluation, such as the effective value of the name attribute of xsl:element or the string supplied as the first argument to the key function.

5.3 Expressions

XSLT uses the expression language defined by XPath 3.0 [XPath 3.0]. Expressions are used in XSLT for a variety of purposes including:

  • selecting nodes for processing;

  • specifying conditions for different ways of processing a node;

  • generating text to be inserted in a result tree.

[Definition: Within this specification, the term XPath expression, or simply expression, means a string that matches the production ExprXP30 defined in [XPath 3.0].]

An XPath expression may occur as the value of certain attributes on XSLT-defined elements, and also within curly brackets in attribute value templates and text value templates.

Except where forwards compatible behavior is enabled (see 3.11 Forwards Compatible Processing), it is a static error if the value of such an attribute, or the text between curly brackets in an attribute value template or text value template, does not match the XPath production ExprXP30, or if it fails to satisfy other static constraints defined in the XPath specification, for example that all variable references must refer to variables that are in scope. Error codes are defined in [XPath 3.0].

The transformation fails with a dynamic error if any XPath expression is evaluated and raises a dynamic error. Error codes are defined in [XPath 3.0].

The transformation fails with a type error if an XPath expression raises a type error, or if the result of evaluating the XPath expression is evaluated and raises a type error, or if the XPath processor signals a type error during static analysis of an expression. Error codes are defined in [XPath 3.0].

[Definition: The context within a stylesheet where an XPath expression appears may specify the required type of the expression. The required type indicates the type of the value that the expression is expected to return.] If no required type is specified, the expression may return any value: in effect, the required type is then item()*.

[Definition: Except where otherwise indicated, the actual value of an expression is converted to the required type using the function conversion rules. These are the rules defined in [XPath 3.0] for converting the supplied argument of a function call to the required type of that argument, as defined in the function signature. The relevant rules are those that apply when XPath 1.0 compatibility mode is set to false.]

This specification also invokes the XPath 3.0 function conversion rules to convert the result of evaluating an XSLT sequence constructor to a required type (for example, the sequence constructor enclosed in an xsl:variable, xsl:template, or xsl:function element).

Any dynamic error or type error that occurs when applying the function conversion rules to convert a value to a required type results in the transformation failing, in the same way as if the error had occurred while evaluating an expression.

Note:

Note the distinction between the two kinds of error that may occur. Attempting to convert an integer to a date is a type error, because such a conversion is never possible. Type errors can be reported statically if they can be detected statically, whether or not the construct in question is ever evaluated. Attempting to convert the string 2003-02-29 to a date is a dynamic error rather than a type error, because the problem is with this particular value, not with its type. Dynamic errors are reported only if the instructions or expressions that cause them are actually evaluated.

5.4 The Static and Dynamic Context

XPath defines the concept of an expression contextXP30 which contains all the information that can affect the result of evaluating an expression. The expression context has two parts, the static contextXP30, and the dynamic contextXP30. The components that make up the expression context are defined in the XPath specification (see Section 2.1 Expression Context XP30). This section describes the way in which these components are initialized when an XPath expression is contained within an XSLT stylesheet.

As well as providing values for the static and dynamic context components defined in the XPath specification, XSLT defines additional context components of its own. These context components are used by XSLT instructions (for example, xsl:next-match and xsl:apply-imports), and also by the functions in the extended function library described in this specification.

The following four sections describe:

5.4.1 Initializing the Static Context
5.4.2 Additional Static Context Components used by XSLT
5.4.3 Initializing the Dynamic Context
5.4.4 Additional Dynamic Context Components used by XSLT

5.4.1 Initializing the Static Context

The static contextXP30 of an XPath expression appearing in an XSLT stylesheet is initialized as follows. In these rules, the term containing element means the element within the stylesheet that is the parent of the attribute or text node whose value contains the XPath expression in question, and the term enclosing element means the containing element or any of its ancestors.

5.4.2 Additional Static Context Components used by XSLT

Some of the components of the XPath static context are used also by XSLT elements. For example, the xsl:sort element makes use of the collations defined in the static context, and attributes such as type and as may reference types defined in the in-scope schema components.

Many top-level declarations in a stylesheet, and attributes on the xsl:stylesheet element, affect the behavior of instructions within the stylesheet. Each of these constructs is described in its appropriate place in this specification.

A number of these constructs are of particular significance because they are used by functions defined in XSLT, which are added to the library of functions available for use in XPath expressions within the stylesheet. These are:

  • The set of named keys, used by the key function

  • The values of system properties, used by the system-property function

  • The set of available instructions, used by the element-available function

A dynamic function call clears the first of these components: this means that a dynamic call to the key function will always raise a dynamic error (the key name is unknown). The values of system properties and the set of available instructions, by contrast, reflect the capabilities and configuration of the processor rather than values specific to the stylesheet code itself; the result of a dynamic call to system-property or element-available will reflect the information available to the processor at evaluation time.

Note:

If these functions are called within a static expression, the results will reflect the capabilities and configuration of the processor used to perform static analysis, while if they are called elsewhere, the results should reflect the capabilities and configuration of the processor used to perform dynamic evaluation, which might give a different result. These calls should not be pre-evaluated at compile time unless it is known that this will give the same result.

5.4.3 Initializing the Dynamic Context

For convenience, the dynamic context is described in two parts: the focus, which represents the place in the source document that is currently being processed, and a collection of additional context variables.

A number of functions specified in [Functions and Operators] are defined to be deterministicFO30, meaning that if they are called twice during the same execution scopeFO30, with the same arguments, then they return the same results (see Section 1.6 Terminology FO30). In XSLT, the execution of a stylesheet defines the execution scope. This means, for example, that if the function current-dateTimeFO30 is called repeatedly during a transformation, it produces the same result each time. By implication, the components of the dynamic context on which these functions depend are also stable for the duration of the transformation. Specifically, the following components defined in Section 2.1.2 Dynamic Context XP30 must be stable: function implementations, current dateTime, implicit timezone, available documents, available collections, and default collection. The values of global variables and stylesheet parameters are also stable for the duration of a transformation. The focus is not stable; the additional dynamic context components defined in 5.4.4 Additional Dynamic Context Components used by XSLT are also not stable.

As specified in [Functions and Operators], implementations may provide user options that relax the requirement for the docFO30 and collectionFO30 functions (and therefore, by implication, the document function) to return stable results. By default, however, the functions must be stable. The manner in which such user options are provided, if at all, is implementation-defined.

XPath expressions contained in [xsl:]use-when attributes are not considered to be evaluated "during the transformation" as defined above. For details see 3.14 Conditional Element Inclusion.

[Definition: A component of the context that has no value is said to be absent.] This is a distinguishable state, and is not the same as having the empty sequence as its value.

5.4.3.1 Maintaining Position: the Focus

[Definition: When a sequence constructor is evaluated, the processor keeps track of which items are being processed by means of a set of implicit variables referred to collectively as the focus.] More specifically, the focus consists of the following three values:

  • [Definition: The context item is the item currently being processed. An item (see [Data Model]) is either an atomic value (such as an integer, date, or string), a node, or a function item. The context item is initially set to the initial context item supplied when the transformation is invoked (see 2.3 Initiating a Transformation). It changes whenever instructions such as xsl:apply-templates and xsl:for-each are used to process a sequence of items; each item in such a sequence becomes the context item while that item is being processed.] The context item is returned by the XPath expression . (dot).

  • [Definition: The context position is the position of the context item within the sequence of items currently being processed. It changes whenever the context item changes. When an instruction such as xsl:apply-templates or xsl:for-each is used to process a sequence of items, the first item in the sequence is processed with a context position of 1, the second item with a context position of 2, and so on.] The context position is returned by the XPath expression position().

  • [Definition: The context size is the number of items in the sequence of items currently being processed. It changes whenever instructions such as xsl:apply-templates and xsl:for-each are used to process a sequence of items; during the processing of each one of those items, the context size is set to the count of the number of items in the sequence (or equivalently, the position of the last item in the sequence).] The context size is returned by the XPath expression last().

[Definition: If the context item is a node (as distinct from an atomic value such as an integer), then it is also referred to as the context node. The context node is not an independent variable, it changes whenever the context item changes. When the context item is an atomic value or a function item, there is no context node.] The context node is returned by the XPath expression self::node(), and it is used as the starting node for all relative path expressions.

Where the containing element of an XPath expression is an instruction or a literal result element, the initial context item, context position, and context size for the XPath expression are the same as the context item, context position, and context size for the evaluation of the containing instruction or literal result element.

For an XPath expression contained in a value template, the initial context item, context position, and context size for the XPath expression are the same as the context item, context position, and context size for the evaluation of the containing sequence constructor.

In other cases (for example, where the containing element is xsl:sort, xsl:with-param, or xsl:key), the rules are given in the specification of the containing element.

The current function can be used within any XPath expression to select the item that was supplied as the context item to the XPath expression by the XSLT processor. Unlike . (dot) this is unaffected by changes to the context item that occur within the XPath expression. The current function is described in 20.3.1 fn:current.

On completion of an instruction that changes the focus (such as xsl:apply-templates or xsl:for-each), the focus reverts to its previous value.

When a stylesheet function is called, the focus within the body of the function is initially absent. The focus is also absent on initial entry to the stylesheet if no initial context item is supplied.

When the focus is absent, evaluation of any expression that references the context item, context position, or context size results in a dynamic error [ERR XPDY0002] XP30

The description above gives an outline of the way the focus works. Detailed rules for the effect of each instruction are given separately with the description of that instruction. In the absence of specific rules, an instruction uses the same focus as its parent instruction.

[Definition: A singleton focus based on an item J has the context item (and therefore the context node, if J is a node) set to J, and the context position and context size both set to 1 (one).]

5.4.3.2 Other Components of the XPath Dynamic Context

The previous section explained how the focus for an XPath expression appearing in an XSLT stylesheet is initialized. This section explains how the other components of the dynamic contextXP30 of an XPath expression are initialized.

  • The dynamic variablesXP30 are the current values of the in-scope variable binding elements.

  • The current date and time represents an implementation-dependent point in time during processing of the transformation; it does not change during the course of the transformation.

  • The implicit timezoneXP30 is implementation-defined.

  • The available documentsXP30, and the available collectionsXP30 are determined as part of the process for initiating a transformation (see 2.3 Initiating a Transformation).

    The available documentsXP30 are defined as part of the XPath 3.0 dynamic context to support the docFO30 function, but this component is also referenced by the similar XSLT document function: see 20.1 fn:document. This variable defines a mapping between URIs passed to the docFO30 or document function and the document nodes that are returned.

    The mapping from URIs to document nodes is affected by xsl:strip-space declarations and by the input-type-annotations attribute, and may therefore vary from one package to another.

    Note:

    Defining this as part of the evaluation context is a formal way of specifying that the way in which URIs get turned into document nodes is outside the control of the language specification, and depends entirely on the run-time environment in which the transformation takes place.

    The XSLT-defined document function allows the use of URI references containing fragment identifiers. The interpretation of a fragment identifier depends on the media type of the resource representation. Therefore, the information supplied in available documentsXP30 for XSLT processing must provide not only a mapping from URIs to document nodes as required by XPath, but also a mapping from URIs to media types.

  • The default collectionXP30 is implementation-defined. This allows options such as setting the default collection to be an empty sequence, or to be absent.

5.4.4 Additional Dynamic Context Components used by XSLT

In addition to the values that make up the focus, an XSLT processor maintains a number of other dynamic context components that reflect aspects of the evaluation context. These components are fully described in the sections of the specification that maintain and use them. They are:

The following non-normative table summarizes the initial state of each of the components in the evaluation context, and the instructions which cause the state of the component to change.

Component Initial Setting Set by Cleared by
focus singleton focus based on the initial context item if supplied xsl:apply-templates, xsl:for-each, xsl:for-each-group, xsl:analyze-string, evaluation of patterns Calls to stylesheet functions
current template rule If a named template is supplied as the entry point to the transformation, then absent; otherwise the initial template xsl:apply-templates, xsl:apply-imports, xsl:next-match xsl:for-each, xsl:for-each-group, xsl:analyze-string, xsl:iterate, xsl:stream, xsl:merge, xsl:evaluate, and calls to stylesheet functions, and dynamic function calls. Also cleared while evaluating global variables or default values of stylesheet parameters, patterns, and the sequence constructors contained in xsl:key and xsl:sort.
current mode the initial mode xsl:apply-templates Calls to stylesheet functions. Also cleared while evaluating global variables and stylesheet parameters, patterns, and the sequence constructor contained in xsl:key or xsl:sort. Clearing the current mode causes the current mode to be set to the default (unnamed) mode.
current group absent xsl:for-each-group, xsl:merge Calls to stylesheet functions, dynamic function calls, evaluation of global variables, stylesheet parameters, and patterns, calls on xsl:for-each-group with a bind-group attribute.
current grouping key absent xsl:for-each-group, xsl:merge Calls to stylesheet functions, dynamic function calls, evaluation of global variables, stylesheet parameters, and patterns, calls on xsl:for-each-group with a bind-grouping-key attribute or with a group-starting-with or group-ending-with attribute.
current captured substrings empty sequence xsl:matching-substring xsl:non-matching-substring; Calls to stylesheet functions, dynamic function calls, evaluation of global variables, stylesheet parameters, and patterns
output state final output state Set to temporary output state by instructions such as xsl:variable, xsl:attribute, etc., and by calls on stylesheet functions None

[Definition: The term non-contextual function call is used to refer to function calls that do not pass the dynamic context to the called function. This includes all calls on stylesheet functions and all dynamic function invocationsXP30, (that is calls to function items as permitted by XPath 3.0). It does not include calls to all core functions in particular those that explicitly depend on the context, such as the current-group and regex-group functions. It is implementation-defined whether, and under what circumstances, calls to extension functions are non-contextual.]

Named function references (such as position#0) and calls on function-lookupFO30 (for example, function-lookup("position", 0)) are defined to retain the XPath static and dynamic context at the point of invocation as part of the closure of the resulting function item, and to use this preserved context when a dynamic function call is subsequently made using the function item. This rule does not extend to the XSLT extensions to the dynamic context defined in this section. If a dynamic function call is made that depends on the XSLT part of the dynamic context (for example, regex-group#1(2)), then the relevant components of the context are cleared as described in the table above.

5.5 Defining a Decimal Format

The definition of the format-numberFO30 function is now in [Functions and Operators]. What remains here is the definition of the xsl:decimal-format declaration, which provides the context for this function when used in an XSLT stylesheet.

<!-- Category: declaration -->
<xsl:decimal-format
  name? = eqname
  decimal-separator? = char
  grouping-separator? = char
  infinity? = string
  minus-sign? = char
  NaN? = string
  percent? = char
  per-mille? = char
  zero-digit? = char
  digit? = char
  pattern-separator? = char />

The xsl:decimal-format element sets the statically known decimal formats component of the static context for XPath expressions, which controls the interpretation of a picture string used by the format-numberFO30 function.

[Definition: The picture string is the string supplied as the second argument of the format-numberFO30 function.]

Note:

The format-numberFO30 function, previously defined in this specification, is now a core function defined in [Functions and Operators].

A package may contain multiple xsl:decimal-format declarations and may include or import stylesheet modules that also contain xsl:decimal-format declarations. The name of an xsl:decimal-format declaration is the value of its name attribute, if any.

[Definition: All the xsl:decimal-format declarations in a package that share the same name are grouped into a named decimal format; those that have no name are grouped into a single unnamed decimal format.]

The attributes of the xsl:decimal-format declaration define the value of the corresponding attribute in the relevant decimal format in the Statically known decimal formatsXP30 component of the static context for all XPath expressions in the package. The attribute names used in the XSLT 3.0 syntax are the same as the attribute names used in the definition of the static context, except that the digit attribute of xsl:decimal-format corresponds to the digit-sign attribute in the static context.

The scope of an xsl:decimal-format name is the package in which it is declared; the name is available for use only in calls to format-numberFO30 that appear within the same package.

If a package does not contain a declaration of the unnamed decimal format, a declaration equivalent to an xsl:decimal-format element with no attributes is implied.

The attributes of the xsl:decimal-format declaration establish values for a number of variables used as input to the algorithm followed by the format-numberFO30 function. An outline of the purpose of each attribute is given below; however, the definitive explanations are given as part of the specification of format-numberFO30.

For any named decimal format, the effective value of each attribute is taken from an xsl:decimal-format declaration that has that name, and that specifies an explicit value for the required attribute. If there is no such declaration, the default value of the attribute is used. If there is more than one such declaration, the one with highest import precedence is used.

For any unnamed decimal format, the effective value of each attribute is taken from an xsl:decimal-format declaration that is unnamed, and that specifies an explicit value for the required attribute. If there is no such declaration, the default value of the attribute is used. If there is more than one such declaration, the one with highest import precedence is used.

[ERR XTSE1290] It is a static error if a named or unnamed decimal format contains two conflicting values for the same attribute in different xsl:decimal-format declarations having the same import precedence, unless there is another definition of the same attribute with higher import precedence.

The following attributes control the interpretation of characters in the picture string supplied to the format-numberFO30 function, and also specify characters that may appear in the result of formatting the number. In each case the value must be a single character [see ERR XTSE0020].

  • decimal-separator specifies the character used for the decimal-separator-sign; the default value is the period character (.)

  • grouping-separator specifies the character used for the grouping-sign, which is typically used as a thousands separator; the default value is the comma character (,)

  • percent specifies the character used for the percent-sign; the default value is the percent character (%)

  • per-mille specifies the character used for the per-mille-sign; the default value is the Unicode per-mille character (#x2030)

  • zero-digit specifies the character used for the digit-zero-sign; the default value is the digit zero (0). This character must be a digit (category Nd in the Unicode property database), and it must have the numeric value zero. This attribute implicitly defines the Unicode character that is used to represent each of the values 0 to 9 in the final result string: Unicode is organized so that each set of decimal digits forms a contiguous block of characters in numerical sequence.

[ERR XTSE1295] It is a static error if the character specified in the zero-digit attribute is not a digit or is a digit that does not have the numeric value zero.

The following attributes control the interpretation of characters in the picture string supplied to the format-numberFO30 function. In each case the value must be a single character [see ERR XTSE0020].

  • digit specifies the character used for the digit-sign in the picture string; the default value is the number sign character (#)

  • pattern-separator specifies the character used for the pattern-separator-sign, which separates positive and negative sub-pictures in a picture string; the default value is the semi-colon character (;)

The following attributes specify characters or strings that may appear in the result of formatting the number:

  • infinity specifies the string used for the infinity-symbol; the default value is the string Infinity

  • NaN specifies the string used for the NaN-symbol, which is used to represent the value NaN (not-a-number); the default value is the string NaN

  • minus-sign specifies the character used for the minus-symbol; the default value is the hyphen-minus character (-, #x2D). The value must be a single character.

[ERR XTSE1300] It is a static error if, for any named or unnamed decimal format, the variables representing characters used in a picture string do not each have distinct values. These variables are decimal-separator-sign, grouping-sign, percent-sign, per-mille-sign, digit-zero-sign, digit-sign, and pattern-separator-sign.

Every (named or unnamed) decimal format defined in a package is added to the statically known decimal formatsXP30 in the static contextXP30 of every expression in the package, excluding expressions appearing in [xsl:]use-when attributes.

5.6 Patterns

In XSLT 3.0, patterns can match any kind of item: atomic values and function items as well as nodes.

A template rule identifies the items to which it applies by means of a pattern. As well as being used in template rules, patterns are used for numbering (see 12 Numbering), for grouping (see 14 Grouping), and for declaring keys (see 20.2 Keys).

[Definition: A pattern specifies a set of conditions on an item. An item that satisfies the conditions matches the pattern; an item that does not satisfy the conditions does not match the pattern.]

There are two basic kinds of pattern: predicate patterns, and path patterns. Patterns may also be formed by combining other patterns using union, intersection, and difference operators.

A predicate pattern uses the syntax .[ Expr ] written with zero or or more predicates in square brackets; it matches an item if each of the predicates matches the context item. The detailed semantics are given in 5.6.3 The Meaning of a Pattern. This construct can be used to match items of any kind (nodes, atomic values, and function items). For example, the pattern .[starts-with(., '$')] matches any string that starts with the character "$", or a node whose atomized value starts with "$". This example shows a predicate pattern with a single predicate, but the grammar allows any number of predicates (zero or more).

The syntax for path patterns is a subset of the syntax for expressions. Path patterns are used only for matching nodes; an item other than a node will never match a path pattern. As explained in detail below, a node matches a path pattern if the node can be selected by deriving an equivalent expression, and evaluating this expression with respect to some possible context.

Note:

The specification uses the phrases an item matches a pattern and a pattern matches an item interchangeably. They are equivalent: an item matches a pattern if and only if the pattern matches the item.

5.6.1 Examples of Patterns

Example: Patterns

Here are some examples of patterns:

  • . matches any item.

  • * matches any element.

  • para matches any para element.

  • chapter|appendix matches any chapter element and any appendix element.

  • olist/entry matches any entry element with an olist parent.

  • appendix//para matches any para element with an appendix ancestor element.

  • schema-element(us:address) matches any element that is annotated as an instance of the type defined by the schema element declaration us:address, and whose name is either us:address or the name of another element in its substitution group.

  • attribute(*, xs:date) matches any attribute annotated as being of type xs:date.

  • / matches a document node.

  • document-node() matches a document node.

  • document-node(schema-element(my:invoice)) matches the document node of a document whose document element is named my:invoice and matches the type defined by the global element declaration my:invoice.

  • text() matches any text node.

  • namespace-node() matches any namespace node.

  • node() matches any node other than an attribute node, namespace node, or document node.

  • id("W33") matches the element with unique ID W33.

  • para[1] matches any para element that is the first para child element of its parent. It also matches a parentless para element.

  • //para matches any para element that has a parent node.

  • bullet[position() mod 2 = 0] matches any bullet element that is an even-numbered bullet child of its parent.

  • div[@class="appendix"]//p matches any p element with a div ancestor element that has a class attribute with value appendix.

  • @class matches any class attribute (not any element that has a class attribute).

  • @* matches any attribute node.

  • $xyz matches any node that is present in the value of the variable $xyz.

  • $xyz//* matches any element that is a descendant of a node that is present in the value of the variable $xyz.

  • doc('product.xml')//* matches any element within the document whose document URI is 'product.xml'.

  • .[. instance of node()] matches any node. (Note the distinction from the pattern node().)

  • .[. instance of xs:date] matches any atomic value of type xs:date (or a type derived by restriction from xs:date).

  • .[. gt current-date()] matches any date in the future. It can match an atomic value of type xs:date or xs:untypedAtomic, or a node whose atomized value is an xs:date or xs:untypedAtomic value.

  • .[starts-with(., 'e')] matches any node or atomic value that after conversion to a string using the function conversion rules starts with the letter 'e'.

  • .[. instance of function(*)] matches any function item.

  • .[$f(.)] matches any item provided that the call on the function bound to the variable $f returns a result whose effective boolean value is true.

5.6.2 Syntax of Patterns

[ERR XTSE0340] Where an attribute is defined to contain a pattern, it is a static error if the pattern does not match the production Pattern30.

The grammar for patterns uses the notation defined in Section A.1.1 Notation XP30.

The lexical rules for patterns are the same as the lexical rules for XPath expressions, as defined in Section A.2 Lexical structure XP30. Comments are permitted between tokens, using the syntax (: ... :). All other provisions of the XPath grammar apply where relevant, for example the rules for whitespace handling and extra-grammatical constraints.

Patterns
[1]    Pattern30    ::=    PredicatePattern | UnionExprP
[2]    PredicatePattern    ::=    "." PredicateListXP30
[3]    UnionExprP    ::=    IntersectExceptExprP (("union" | "|") IntersectExceptExprP)*
[4]    IntersectExceptExprP    ::=    PathExprP (("intersect" | "except") PathExprP)*
[5]    PathExprP    ::=    RootedPath
| ("/" RelativePathExprP?)
| ("//" RelativePathExprP)
| RelativePathExprP
[6]    RootedPath    ::=    (VarRefXP30 | FunctionCallP) PredicateListXP30 (("/" | "//") RelativePathExprP)?
[7]    FunctionCallP    ::=    OuterFunctionName ArgumentListP
[8]    OuterFunctionName    ::=    "doc" | "id" | "element-with-id" | "key" | PrefixedQName | URIQualifiedNameXP30
[10]    ArgumentListP    ::=    "(" (ArgumentP ("," ArgumentP)*)? ")"
[11]    ArgumentP    ::=    VarRefXP30 | LiteralXP30
[12]    RelativePathExprP    ::=    StepExprP (("/" | "//") StepExprP)*
[13]    StepExprP    ::=    PostfixExprP | AxisStepP
[14]    PostfixExprP    ::=    ParenthesizedExprP PredicateListXP30
[15]    ParenthesizedExprP    ::=    "(" UnionExprP ")"
[16]    AxisStepP    ::=    ForwardStepP PredicateListXP30
[17]    ForwardStepP    ::=    (ForwardAxisP NodeTestXP30) | AbbrevForwardStepXP30
[18]    ForwardAxisP    ::=    ("child" "::")
| ("descendant" "::")
| ("attribute" "::")
| ("self" "::")
| ("descendant-or-self" "::")
| ("namespace" "::")
[122]    PrefixedQName    ::=    NCNameXP30 ":" NCNameXP30

The names of these constructs are chosen to align with the XPath 3.0 grammar. Constructs whose names are suffixed with P are restricted forms of the corresponding XPath 3.0 construct without the suffix. Constructs labelled with the suffix "XP30" are defined in [XPath 3.0].

In a FunctionCallP, the EQName used for the function name must have local part doc, id, element-with-id, or key, and must use the standard function namespace either explicitly or implicitly.

Note:

As with XPath expressions, the pattern / union /* can be parsed in two different ways, and the chosen interpretation is to treat union as an element name rather than as an operator. The other interpretation can be achieved by writing (/) union (/*)

5.6.3 The Meaning of a Pattern

The meaning of a pattern is defined formally as follows, where "if" is to be read as "if and only if".

If the pattern is a PredicatePattern PP, then it matches an item J if the XPath expression taking the same form as PP returns a non-empty sequence when evaluated with a singleton focus based on J.

Note:

The pattern ., which is a PredicatePattern with an empty PredicateList, matches every item.

A predicate with the numeric value 1 (one) always matches, and a predicate with any other numeric value never matches. Numeric predicates in a PredicatePattern are therefore not useful, but are defined this way in the interests of consistency with XPath.

Otherwise (the pattern is a PathPattern), the pattern is converted to an expression, called the equivalent expression. The equivalent expression to a Pattern is the XPath expression that takes the same lexical form as the Pattern as written, with the following adjustment:

  • If any PathExprP in the Pattern is a RelativePathExprP, then the first StepExprP PS of this RelativePathExprP is adjusted to allow it to match a parentless element, attribute, or namespace node. The adjustment depends on the axis used in this step, whether it appears explicitly or implicitly (according to the rules of Section 3.3.5 Abbreviated Syntax XP30), and is made as follows:

    1. If the NodeTest in PS is document-node() (optionally with arguments), and if no explicit axis is specified, then the axis in step PS is taken as self rather than child.

    2. If PS uses the child axis (explicitly or implicitly), and if the NodeTest in PS is not document-node() (optionally with arguments), then the axis in step PS is replaced by child-or-top, which is defined as follows. If the context node is a parentless element, comment, processing-instruction, or text node then the child-or-top axis selects the context node; otherwise it selects the children of the context node. It is a forwards axis whose principal node kind is element.

    3. If PS uses the attribute axis (explicitly or implicitly), then the axis in step PS is replaced by attribute-or-top, which is defined as follows. If the context node is an attribute node with no parent, then the attribute-or-top axis selects the context node; otherwise it selects the attributes of the context node. It is a forwards axis whose principal node kind is attribute.

    4. If PS uses the namespace axis (explicitly or implicitly), then the axis in step PS is replaced by namespace-or-top, which is defined as follows. If the context node is a namespace node with no parent, then the namespace-or-top axis selects the context node; otherwise it selects the namespace nodes of the context node. It is a forwards axis whose principal node kind is namespace.

    The axes child-or-top, attribute-or-top, and namespace-or-top are introduced only for definitional purposes. They cannot be used explicitly in a user-written pattern or expression.

    Note:

    The purpose of this adjustment is to ensure that a pattern such as person matches any element named person, even if it has no parent; and similarly, that the pattern @width matches any attribute named width, even a parentless attribute. The rule also ensures that a pattern using a NodeTest of the form document-node(...) matches a document node. The pattern node() will match any element, text node, comment, or processing instruction, whether or not it has a parent. For backwards compatibility reasons, the pattern node(), when used without an explicit axis, does not match document nodes, attribute nodes, or namespace nodes. The rules are also phrased to ensure that positional patterns of the form para[1] continue to count nodes relative to their parent, if they have one. To match any node at all, XSLT 3.0 allows the pattern .[. instance of node()] to be used.

The meaning of the pattern is then defined in terms of the semantics of the equivalent expression, denoted below as EE.

Specifically, an item N matches a pattern P if the following applies, where EE is the equivalent expression to P:

  1. N is a node, and the result of evaluating the expression root(.)//(EE) with a singleton focus based on N is a sequence that includes the node N

If a pattern appears in an attribute of an element that is processed with XSLT 1.0 behavior (see 3.10 Backwards Compatible Processing), then the semantics of the pattern are defined on the basis that the equivalent XPath expression is evaluated with XPath 1.0 compatibility mode set to true.

Example: The Semantics of Path Patterns

The path pattern p matches any p element, because a p element will always be present in the result of evaluating the expression root(.)//(child-or-top::p). Similarly, / matches a document node, and only a document node, because the result of the expression root(.)//(/) returns the root node of the tree containing the context node if and only if it is a document node.

The path pattern node() matches all nodes selected by the expression root(.)//(child-or-top::node()), that is, all element, text, comment, and processing instruction nodes, whether or not they have a parent. It does not match attribute or namespace nodes because the expression does not select nodes using the attribute or namespace axes. It does not match document nodes because for backwards compatibility reasons the child-or-top axis does not match a document node.

The path pattern $V matches all nodes selected by the expression root(.)//($V), that is, all nodes in the value of $V (which will typically be a global variable, though when the pattern is used in contexts such as the xsl:number or xsl:for-each-group instructions, it can also be a local variable).

The path pattern doc('product.xml')//product matches all nodes selected by the expression root(.)//(doc('product.xml')//product), that is, all product elements in the document whose URI is product.xml.

Although the semantics of path patterns are specified formally in terms of expression evaluation, it is possible to understand pattern matching using a different model. A path pattern such as book/chapter/section can be examined from right to left. A node will only match this pattern if it is a section element; and then, only if its parent is a chapter; and then, only if the parent of that chapter is a book. When the pattern uses the // operator, one can still read it from right to left, but this time testing the ancestors of a node rather than its parent. For example appendix//section matches every section element that has an ancestor appendix element.

The formal definition, however, is useful for understanding the meaning of a pattern such as para[1]. This matches any node selected by the expression root(.)//(child-or-top::para[1]): that is, any para element that is the first para child of its parent, or a para element that has no parent.

Note:

An implementation, of course, may use any algorithm it wishes for evaluating patterns, so long as the result corresponds with the formal definition above. An implementation that followed the formal definition by evaluating the equivalent expression and then testing the membership of a specific node in the result would probably be very inefficient.

5.6.4 Errors in Patterns

A dynamic error or type error that occurs during the evaluation of a pattern against a particular item has the effect that the item being tested is treated as not matching the pattern. The error does not cause the transformation to fail, and cannot be caught by a try/catch expression surrounding the instruction that causes the pattern to be evaluated.

Note:

The reason for this provision is that it is difficult for the stylesheet author to predict which predicates in a pattern will actually be evaluated. In the case of match patterns in template rules, it is not even possible to predict which patterns will be evaluated against a particular node.

There is a risk that ignoring errors in this way may make programming mistakes harder to debug. Implementations may mitigate this by providing warnings or other diagnostics when evaluation of a pattern triggers an error condition.

Static errors in patterns, including dynamic and type errors that are signaled statically as permitted by the specification, are reported in the normal way and cause the transformation to fail.

5.7 Value Templates

The string value of an attribute or text node in the stylesheet may in particular circumstances contain embedded expressions enclosed between curly brackets. Attributes and text nodes that use (or are permitted to use) this mechanism are referred to respectively as attribute value templates and text value templates..

[Definition: Collectively, attribute value templates and text value templates are referred to as value templates.]

A value template is a string consisting of an alternating sequence of fixed parts and variable parts. A variable part consists of an XPath expression enclosed in curly brackets ({}). A fixed part may contain any characters, except that a left curly bracket must be written as {{ and a right curly bracket must be written as }}.

Note:

An expression within a variable part may contain an unescaped curly bracket within a StringLiteralXP30 or within a comment.

Currently no XPath expression starts with an opening curly bracket, so the use of {{ creates no ambiguity. If an enclosed expression ends with a closing curly bracket, no whitespace is required between this and the closing delimiter.

[ERR XTSE0350] It is a static error if an unescaped left curly bracket appears in a fixed part of a value template without a matching right curly bracket.

It is a static error if the string contained between matching curly brackets in a value template does not match the XPath production ExprXP30, or if it contains other XPath static errors. The error is signaled using the appropriate XPath error code.

[ERR XTSE0370] It is a static error if an unescaped right curly bracket occurs in a fixed part of a value template.

[Definition: The result of evaluating a value template is referred to as its effective value.] The effective value is the string obtained by concatenating the expansions of the fixed and variable parts:

  • The expansion of a fixed part is obtained by replacing any double curly brackets ({{ or }}) by the corresponding single curly bracket.

  • The expansion of a variable part is obtained by evaluating the enclosed XPath expression and converting the resulting value to a string. This conversion is done using the rules given in 5.8.2 Constructing Simple Content.

Note:

This process can generate dynamic errors, for example if the sequence contains an element with a complex content type (which cannot be atomized).

In the case of an attribute value template, the effective value becomes the string value of the new attribute node. In the case of a text value template, the effective value becomes the string value of the new text node.

5.7.1 Attribute Value Templates

[Definition: In an attribute that is designated as an attribute value template, such as an attribute of a literal result element, an expression can be used by surrounding the expression with curly brackets ({}), following the general rules for value templates].

Curly brackets are not treated specially in an attribute value in an XSLT stylesheet unless the attribute is specifically designated as one that permits an attribute value template; in an element syntax summary, the value of such attributes is surrounded by curly brackets.

Note:

Not all attributes are designated as attribute value templates. Attributes whose value is an expression or pattern, attributes of declaration elements and attributes that refer to named XSLT objects are generally not designated as attribute value templates (an exception is the format attribute of xsl:result-document). Namespace declarations are not XDM attribute nodes and are therefore never treated as attribute value templates.

If the element containing the attribute is processed with XSLT 1.0 behavior, then the rules for converting the value of the expression to a string (given in 5.7 Value Templates) are modified as follows. After atomizing the result of the expression, all items other than the first item in the resulting sequence are discarded, and the effective value is obtained by converting the first item in the sequence to a string. If the atomized sequence is empty, the result is a zero-length string.

Note:

The above rule applies to attribute value templates but not to text value templates, since the latter were not available in XSLT 1.0.

Example: Attribute Value Templates

The following example creates an img result element from a photograph element in the source; the value of the src and width attributes are computed using XPath expressions enclosed in attribute value templates:

<xsl:variable name="image-dir" select="'/images'"/>

<xsl:template match="photograph">
  <img src="{$image-dir}/{href}" width="{size/@width}"/>
</xsl:template>

With this source

<photograph>
  <href>headquarters.jpg</href>
  <size width="300"/>
</photograph>

the result would be

<img src="/images/headquarters.jpg" width="300"/>

 

Example: Producing a Space-Separated List

The following example shows how the values in a sequence are output as a space-separated list. The following literal result element:

<temperature readings="{10.32, 5.50, 8.31}"/>

produces the output node:

<temperature readings="10.32 5.5 8.31"/>

Curly brackets are not recognized recursively inside expressions.

Example: Curly Brackets can not be Nested

For example:

<a href="#{id({@ref})/title}">

is not allowed. Instead, use simply:

<a href="#{id(@ref)/title}">

5.7.2 Text Value Templates

The standard attribute [xsl:]expand-text may appear on any element in the stylesheet, and determines whether descendant text nodes of that element are treated as text value templates. A text node in the stylesheet is treated as a text value template if (a) it is part of a sequence constructor, (b) there is an ancestor element with an [xsl:]expand-text attribute, and (c) on the innermost ancestor element that has such an attribute, the value of the attribute is yes. The value of the attribute must be yes or no.

This section describes how text nodes appearing in sequence constructors are processed when the effective value is yes. Such text nodes are referred to as text value templates.

[Definition: In a text node that is designated as a text value template, expressions can be used by surrounding each expression with curly brackets ({}).]

The rules for text value templates are given in 5.7 Value Templates. A text node in a sequence constructor whose value is a text value template results in the construction of a text node in the result of the sequence constructor. The string value of that text node is obtained by computing the effective value of the value template.

Note:

The content of an xsl:text element is not a sequence constructor, and therefore cannot contain a text value template.

The result of evaluating a text value template is a (possibly zero-length) text node. This text node becomes part of the result of the containing sequence constructor, and is thereafter handled exactly as if the value had appeared explicitly as a text node in the stylesheet.

The way in which the effective value is computed does not depend on any separator attribute on a containing xsl:value-of or xsl:attribute instruction. The separator attribute only affects how the text node is combined with adjacent items in the result of the containing sequence constructor.

Fixed parts consisting entirely of whitespace are significant and are handled in the same way as any other fixed part. This is different from the default treatment of "boundary space" in XQuery.

Example: Using a text value template to construct message output
<xsl:variable name="id" select="'A123'"/>
<xsl:variable name="step" select="5"/>
<xsl:message expand-text="yes"
     >Processing id={$id}, step={$step}</xsl:message>

This will typically output the message text Processing id=A123, step=5.

 

Example: Using a text value template to define the result of a function
<xsl:function name="f:sum" expand-text="yes" as="xs:integer">
<xsl:param name="x" as="xs:integer"/>
<xsl:param name="y" as="xs:integer"/>
  {$x + $y}
</xsl:function>

Note that although this is a very readable way of expressing the computation performed by the function, the semantics are somewhat complex, and this could mean that execution is inefficient. The function computes the value of $x + $y as an integer, and then constructs a text node containing the string representation of this integer (preceded and followed by whitespace). Because the declared result type of the function is xs:integer, this text node is then atomized, giving an xs:untypedAtomic value, and the xs:untypedAtomic value is then cast to an xs:integer.

Note:

The main motivations for adding text value templates to the XSLT language are firstly, to make it easier to construct parameterized text in contexts such as xsl:value-of and xsl:message, and secondly, to allow use of complex multi-line XPath expressions where maintaining correct indentation is important for readability. The fact that XML processors are required to normalize whitespace in attribute values means that writing such expressions within a select attribute is not ideal.

The facility is only present if enabled using the [xsl:]expand-text attribute. This is partly for backwards compatibility, and partly to avoid creating difficulties when constructing content that is rich in curly brackets, for example Javascript code or CSS style sheets.

5.8 Sequence Constructors

[Definition: A sequence constructor is a sequence of zero or more sibling nodes in the stylesheet that can be evaluated to return a sequence of nodes, atomic values, and function items. The way that the resulting sequence is used depends on the containing instruction.]

Many XSLT elements, and also literal result elements, are defined to take a sequence constructor as their content.

Four kinds of nodes may be encountered in a sequence constructor:

  1. A Text node appearing in the stylesheet (if it has not been removed in the process of whitespace stripping: see 4.2 Stripping Whitespace from the Stylesheet) is processed as follows:

    1. if the effective value of the standard attribute [xsl:]expand-text is no, or in the absence of this attribute, the text node in the stylesheet is copied to create a new parentless text node in the result of the sequence constructor.

      Note:

      For an xsl:text element, the effective value of [xsl:]expand-text is always "no".

    2. Otherwise (the effective value of [xsl:]expand-text is yes), the text node in the stylesheet is processed as described in 5.7.2 Text Value Templates.

  2. A literal result element is evaluated to create a new parentless element node, having the same expanded QName as the literal result element: see 11.1 Literal Result Elements.

  3. An XSLT instruction produces a sequence of zero, one, or more items as its result. For most XSLT instructions, these items are nodes, but some instructions (such as xsl:sequence and xsl:copy-of) can also produce atomic values or function items. Several instructions, such as xsl:element, return a newly constructed parentless node (which may have its own attributes, namespaces, children, and other descendants). Other instructions, such as xsl:if, pass on the items produced by their own nested sequence constructors. The xsl:sequence instruction may return atomic values, function items, or existing nodes.

  4. An extension instruction (see 23.2 Extension Instructions) also produces a sequence of items as its result.

The result of evaluating a sequence constructor is the sequence of items formed by concatenating the results of evaluating each of the nodes in the sequence constructor, retaining order.

There are several ways the result of a sequence constructor may be used.

5.8.1 Constructing Complex Content

This section describes how the sequence obtained by evaluating a sequence constructor may be used to construct the children of a newly constructed document node, or the children, attributes and namespaces of a newly constructed element node. The sequence of items may be obtained by evaluating the sequence constructor contained in an instruction such as xsl:copy, xsl:element, xsl:document, xsl:result-document, or a literal result element.

When constructing the content of an element, the inherit-namespaces attribute of the xsl:element or xsl:copy instruction, or the xsl:inherit-namespaces property of the literal result element, determines whether namespace nodes are to be inherited. The effect of this attribute is described in the rules that follow.

The sequence is processed as follows (applying the rules in the order they are listed):

  1. The containing instruction may generate attribute nodes and/or namespace nodes, as specified in the rules for the individual instruction. For example, these nodes may be produced by expanding an [xsl:]use-attribute-sets attribute, or by expanding the attributes of a literal result element. Any such nodes are prepended to the sequence produced by evaluating the sequence constructor.

  2. Any atomic value in the sequence is cast to a string.

    Note:

    Casting from xs:QName or xs:NOTATION to xs:string always succeeds, because these values retain a prefix for this purpose. However, there is no guarantee that the prefix used will always be meaningful in the context where the resulting string is used.

  3. Any consecutive sequence of strings within the result sequence is converted to a single text node, whose string value contains the content of each of the strings in turn, with a single space (#x20) used as a separator between successive strings.

  4. Any document node within the result sequence is replaced by a sequence containing each of its children, in document order.

  5. Zero-length text nodes within the result sequence are removed.

  6. Adjacent text nodes within the result sequence are merged into a single text node.

  7. Invalid items in the result sequence are detected as follows.

    [ERR XTDE0410] It is a dynamic error if the result sequence used to construct the content of an element node contains a namespace node or attribute node that is preceded in the sequence by a node that is neither a namespace node nor an attribute node.

    [ERR XTDE0420] It is a dynamic error if the result sequence used to construct the content of a document node contains a namespace node or attribute node.

    [ERR XTDE0430] It is a dynamic error if the result sequence contains two or more namespace nodes having the same name but different string values (that is, namespace nodes that map the same prefix to different namespace URIs).

    [ERR XTDE0440] It is a dynamic error if the result sequence contains a namespace node with no name and the element node being constructed has a null namespace URI (that is, it is an error to define a default namespace when the element is in no namespace).

    [ERR XTDE0450] It is a dynamic error if the result sequence contains a function item.

  8. If the result sequence contains two or more namespace nodes with the same name (or no name) and the same string value (that is, two namespace nodes mapping the same prefix to the same namespace URI), then all but one of the duplicate nodes are discarded.

    Note:

    Since the order of namespace nodes is implementation-dependent, it is not significant which of the duplicates is retained.

  9. If an attribute A in the result sequence has the same name as another attribute B that appears later in the result sequence, then attribute A is discarded from the result sequence. Before discarding attribute A, the processor may signal any type errors that would be signaled if attribute B were not present.

  10. Each node in the resulting sequence is attached as a namespace, attribute, or child of the newly constructed element or document node. Conceptually this involves making a deep copy of the node; in practice, however, copying the node will only be necessary if the existing node can be referenced independently of the parent to which it is being attached. When copying an element or processing instruction node, its base URI property is changed to be the same as that of its new parent, unless it has an xml:base attribute (see [XML Base]) that overrides this. If the copied element has an xml:base attribute, its base URI is the value of that attribute, resolved (if it is relative) against the base URI of the new parent node.

  11. If the newly constructed node is an element node, then namespace fixup is applied to this node, as described in 5.8.3 Namespace Fixup.

  12. If the newly constructed node is an element node, and if namespaces are inherited, then each namespace node of the newly constructed element (including any produced as a result of the namespace fixup process) is copied to each descendant element of the newly constructed element, unless that element or an intermediate element already has a namespace node with the same name (or absence of a name) or that descendant element or an intermediate element is in no namespace and the namespace node has no name.

Example: A Sequence Constructor for Complex Content

Consider the following stylesheet fragment:

<td>
  <xsl:attribute name="valign">top</xsl:attribute>
  <xsl:value-of select="@description"/>
</td>

This fragment consists of a literal result element td, containing a sequence constructor that consists of two instructions: xsl:attribute and xsl:value-of. The sequence constructor is evaluated to produce a sequence of two nodes: a parentless attribute node, and a parentless text node. The td instruction causes a td element to be created; the new attribute therefore becomes an attribute of the new td element, while the text node created by the xsl:value-of instruction becomes a child of the td element (unless it is zero-length, in which case it is discarded).

 

Example: Space Separators in Element Content

Consider the following stylesheet fragment:

<doc>
  <e><xsl:sequence select="1 to 5"/></e>
  <f>
    <xsl:for-each select="1 to 5">
      <xsl:value-of select="."/>
    </xsl:for-each>
  </f>
</doc>

This produces the output (when indented):

<doc>
  <e>1 2 3 4 5</e>
  <f>12345</f>
</doc>

The difference between the two cases is that for the e element, the sequence constructor generates a sequence of five atomic values, which are therefore separated by spaces. For the f element, the content is a sequence of five text nodes, which are concatenated without space separation.

It is important to be aware of the distinction between xsl:sequence, which returns the value of its select expression unchanged, and xsl:value-of, which constructs a text node.

5.8.2 Constructing Simple Content

The instructions xsl:attribute, xsl:comment, xsl:processing-instruction, xsl:namespace, and xsl:value-of all create nodes that cannot have children. Specifically, the xsl:attribute instruction creates an attribute node, xsl:comment creates a comment node, xsl:processing-instruction creates a processing instruction node, xsl:namespace creates a namespace node, and xsl:value-of creates a text node. The string value of the new node is constructed using either the select attribute of the instruction, or the sequence constructor that forms the content of the instruction. The select attribute allows the content to be specified by means of an XPath expression, while the sequence constructor allows it to be specified by means of a sequence of XSLT instructions. The select attribute or sequence constructor is evaluated to produce a result sequence, and the string value of the new node is derived from this result sequence according to the rules below.

These rules are also used to compute the effective value of an value template. In this case the sequence being processed is the result of evaluating an XPath expression enclosed between curly brackets, and the separator is a single space character.

  1. Zero-length text nodes in the sequence are discarded.

  2. Adjacent text nodes in the sequence are merged into a single text node.

  3. The sequence is atomized (which may cause a dynamic error).

  4. Every value in the atomized sequence is cast to a string.

  5. The strings within the resulting sequence are concatenated, with a (possibly zero-length) separator inserted between successive strings. The default separator is a single space. In the case of xsl:attribute and xsl:value-of, a different separator can be specified using the separator attribute of the instruction; it is permissible for this to be a zero-length string, in which case the strings are concatenated with no separator. In the case of xsl:comment, xsl:processing-instruction, and xsl:namespace, and when expanding a value template, the default separator cannot be changed.

  6. In the case of xsl:processing-instruction, any leading spaces in the resulting string are removed.

  7. The resulting string forms the string value of the new attribute, namespace, comment, processing-instruction, or text node.

Example: Space Separators in Attribute Content

Consider the following stylesheet fragment:

<doc>
  <xsl:attribute name="e" select="1 to 5"/>
  <xsl:attribute name="f">
    <xsl:for-each select="1 to 5">
      <xsl:value-of select="."/>
    </xsl:for-each>
  </xsl:attribute>
  <xsl:attribute name="g" expand-text="yes">{1 to 5}</xsl:attribute>
</doc>

This produces the output:

<doc e="1 2 3 4 5" f="12345" g="1 2 3 4 5"/>

The difference between the three cases is as follows. For the e attribute, the sequence constructor generates a sequence of five atomic values, which are therefore separated by spaces. For the f attribute, the content is supplied as a sequence of five text nodes, which are concatenated without space separation. For the g attribute, the text value template constructs a text node using the rules for constructing simple content, which insert space separators between atomic values; the text node is then atomized to form the value of the attribute.

Specifying separator="" on the first xsl:attribute instruction would cause the attribute value to be e="12345". A separator attribute on the second xsl:attribute instruction would have no effect, since the separator only affects the way adjacent atomic values are handled: separators are never inserted between adjacent text nodes. A separator on the third xsl:attribute instruction would also have no effect, because text value templates are evaluated without regard to the containing instruction.

Note:

If an attribute value template contains a sequence of fixed and variable parts, no additional whitespace is inserted between the expansions of the fixed and variable parts. For example, the effective value of the attribute a="chapters{4 to 6}" is a="chapters4 5 6".

5.8.3 Namespace Fixup

In a tree supplied to or constructed by an XSLT processor, the constraints relating to namespace nodes that are specified in [Data Model] must be satisfied. For example

  • If an element node has an expanded QName with a non-null namespace URI, then that element node must have at least one namespace node whose string value is the same as that namespace URI.

  • If an element node has an attribute node whose expanded QName has a non-null namespace URI, then the element must have at least one namespace node whose string value is the same as that namespace URI and whose name is non-empty.

  • Every element must have a namespace node whose expanded QName has local-part xml and whose string value is http://www.w3.org/XML/1998/namespace. The namespace prefix xml must not be associated with any other namespace URI, and the namespace URI http://www.w3.org/XML/1998/namespace must not be associated with any other prefix.

  • A namespace node must not have the name xmlns or the string value http://www.w3.org/2000/xmlns/.

[Definition: The rules for the individual XSLT instructions that construct a result tree (see 11 Creating Nodes and Sequences) prescribe some of the situations in which namespace nodes are written to the tree. These rules, however, are not sufficient to ensure that the prescribed constraints are always satisfied. The XSLT processor must therefore add additional namespace nodes to satisfy these constraints. This process is referred to as namespace fixup.]

The actual namespace nodes that are added to the tree by the namespace fixup process are implementation-dependent, provided firstly, that at the end of the process the above constraints must all be satisfied, and secondly, that a namespace node must not be added to the tree unless the namespace node is necessary either to satisfy these constraints, or to enable the tree to be serialized using the original namespace prefixes from the source document or stylesheet.

Namespace fixup must not result in an element having multiple namespace nodes with the same name.

Namespace fixup may, if necessary to resolve conflicts, change the namespace prefix contained in the QName value that holds the name of an element or attribute node. This includes the option to add or remove a prefix. However, namespace fixup must not change the prefix component contained in a value of type xs:QName or xs:NOTATION that forms the typed value of an element or attribute node.

Note:

Namespace fixup is not used to create namespace declarations for xs:QName or xs:NOTATION values appearing in the content of an element or attribute.

Where values acquire such types as the result of validation, namespace fixup does not come into play, because namespace fixup happens before validation: in this situation, it is the user's responsibility to ensure that the element being validated has the required namespace nodes to enable validation to succeed.

Where existing elements are copied along with their existing type annotations (validation="preserve") the rules require that existing namespace nodes are also copied, so that any namespace-sensitive values remain valid.

Where existing attributes are copied along with their existing type annotations, the rules of the XDM data model require that a parentless attribute node cannot contain a namespace-sensitive typed value; this means that it is an error to copy an attribute using validation="preserve" if it contains namespace-sensitive content.

Namespace fixup is applied to every element that is constructed using a literal result element, or one of the instructions xsl:element, xsl:copy, or xsl:copy-of. An implementation is not required to perform namespace fixup for elements in any source document, that is, for a document in the initial input sequence, documents loaded using the document, docFO30 or collectionFO30 function, documents supplied as the value of a stylesheet parameter, or documents returned by an extension function or extension instruction.

Note:

A source document (an input document, a document returned by the document, docFO30 or collectionFO30 functions, a document returned by an extension function or extension instruction, or a document supplied as a stylesheet parameter) is required to satisfy the constraints described in [Data Model], including the constraints imposed by the namespace fixup process. The effect of supplying a pseudo-document that does not meet these constraints is implementation-dependent.

In an Infoset (see [XML Information Set]) created from a document conforming to [Namespaces in XML], it will always be true that if a parent element has an in-scope namespace with a non-empty namespace prefix, then its child elements will also have an in-scope namespace with the same namespace prefix, though possibly with a different namespace URI. This constraint is removed in [Namespaces in XML 1.1]. XSLT 3.0 supports the creation of result trees that do not satisfy this constraint: the namespace fixup process does not add a namespace node to an element merely because its parent node in the result tree has such a namespace node. However, the process of constructing the children of a new element, which is described in 5.8.1 Constructing Complex Content, does cause the namespaces of a parent element to be inherited by its children unless this is prevented using [xsl:]inherit-namespaces="no" on the instruction that creates the parent element.

Note:

This has implications on serialization, defined in [XSLT and XQuery Serialization]. It means that it is possible to create final result trees that cannot be faithfully serialized as XML 1.0 documents. When such a result tree is serialized as XML 1.0, namespace declarations written for the parent element will be inherited by its child elements as if the corresponding namespace nodes were present on the child element, except in the case of the default namespace, which can be undeclared using the construct xmlns="". When the same result tree is serialized as XML 1.1, however, it is possible to undeclare any namespace on the child element (for example, xmlns:foo="") to prevent this inheritance taking place.

5.9 URI References

[Definition: Within this specification, the term URI Reference, unless otherwise stated, refers to a string in the lexical space of the xs:anyURI datatype as defined in [XML Schema Part 2].] Note that this is a wider definition than that in [RFC3986]: in particular, it is designed to accommodate Internationalized Resource Identifiers (IRIs) as described in [RFC3987], and thus allows the use of non-ASCII characters without escaping.

URI References are used in XSLT with three main roles:

  • As namespace URIs

  • As collation URIs

  • As identifiers for resources such as stylesheet modules; these resources are typically accessible using a protocol such as HTTP. Examples of such identifiers are the URIs used in the href attributes of xsl:import, xsl:include, and xsl:result-document.

The rules for namespace URIs are given in [Namespaces in XML] and [Namespaces in XML 1.1]. Those specifications deprecate the use of relative URI references as namespace URIs.

The rules for collation URIs are given in [Functions and Operators].

URI references used to identify external resources must conform to the same rules as the locator attribute (href) defined in section 5.4 of [XLink]. If the URI reference is relative, then it is resolved (unless otherwise specified) against the base URI of the containing element node, according to the rules of [RFC3986], after first escaping all characters that need to be escaped to make it a valid RFC3986 URI reference. (But a relative URI reference in the href attribute of xsl:result-document is resolved against the Base Output URI.)

Other URI references appearing in an XSLT stylesheet document, for example the system identifiers of external entities or the value of the xml:base attribute, must follow the rules in their respective specifications.

The base URI of an element node in the stylesheet is determined as defined in Section 5.2 base-uri Accessor DM30. Some implementations may allow the output of the static analysis phase of stylesheet processing (a "compiled stylesheet") to be evaluated in a different location from that where static analysis took place. Furthermore, stylesheet authors may in such cases which to avoid exposing the location of resources that are private to the development environment. If the base URI of an element in the stylesheet is defined by an absolute URI appearing in an xml:base attribute within the stylesheet, this value must be used as the static base URI. In other cases where processing depends on the static base URI of a stylesheet module, implementations may use different values for the static base URI during static analysis and during dynamic evaluation (for example, an implementation may use different base URIs for resolving xsl:import module references and for resolving a relative reference used as an argument to the docFO30 function). In such cases an implementation must document how the static base URI is computed for each situation in which it is required.

6 Template Rules

Template rules define the processing that can be applied to items that match a particular pattern.

6.1 Defining Templates

<!-- Category: declaration -->
<xsl:template
  match? = pattern
  name? = eqname
  priority? = decimal
  mode? = tokens
  as? = sequence-type
  visibility? = "public" | "private" | "final" | "abstract" >
  <!-- Content: (xsl:context-item?, xsl:param*, sequence-constructor) -->
</xsl:template>

[Definition: An xsl:template declaration defines a template, which contains a sequence constructor ; this sequence constructor is evaluated to determine the result of the template. A template can serve either as a template rule, invoked by matching items against a pattern, or as a named template, invoked explicitly by name. It is also possible for the same template to serve in both capacities.]

[ERR XTSE0500] An xsl:template element must have either a match attribute or a name attribute, or both. An xsl:template element that has no match attribute must have no mode attribute and no priority attribute. An xsl:template element that has no name attribute must have no visibility attribute.

If an xsl:template element has a match attribute, then it is a template rule. If it has a name attribute, then it is a named template.

A template may be invoked in a number of ways, depending on whether it is a template rule, a named template, or both. The result of invoking the template is the result of evaluating the sequence constructor contained in the xsl:template element (see 5.8 Sequence Constructors).

For details of the optional xsl:context-item child element, see 6.7.2 Declaring the context item for a template.

If an as attribute of the xsl:template element is present, the as attribute defines the required type of the result. The result of evaluating the sequence constructor is then converted to the required type using the function conversion rules. If no as attribute is specified, the default value is item()*, which permits any value. No conversion then takes place.

[ERR XTTE0505] It is a type error if the result of evaluating the sequence constructor cannot be converted to the required type.

If the visibility attribute is present with the value abstract then (a) the sequence constructor defining the template body must be empty: that is, the only permitted children are xsl:context-item and xsl:param, and (b) there must be no match attribute.

If the parent of the xsl:template element is an xsl:override element, then there must be a name attribute and no match attribute, and the package that is the target of the containing xsl:use-package element must contain among its components a named template whose symbolic identifier is the same as this named template, and which has a compatible signature.

6.2 Defining Template Rules

This section describes template rules. Named templates are described in 10.1 Named Templates.

A template rule is specified using the xsl:template element with a match attribute. The match attribute is a Pattern that identifies the items to which the rule applies. The result of applying the template rule is the result of evaluating the sequence constructor contained in the xsl:template element, with the matching item used as the context item.

Example: A Simple Template Rule

For example, an XML document might contain:

This is an <emph>important</emph> point.

The following template rule matches emph elements and produces a fo:wrapper element with a font-weight property of bold.

<xsl:template match="emph">
  <fo:wrapper font-weight="bold" 
              xmlns:fo="http://www.w3.org/1999/XSL/Format">
    <xsl:apply-templates/>
  </fo:wrapper>
</xsl:template>

A template rule is evaluated when an xsl:apply-templates instruction selects an item that matches the pattern specified in the match attribute. The xsl:apply-templates instruction is described in the next section. If several template rules match a selected item, only one of them is evaluated, as described in 6.4 Conflict Resolution for Template Rules.

6.3 Applying Template Rules

<!-- Category: instruction -->
<xsl:apply-templates
  select? = expression
  mode? = token >
  <!-- Content: (xsl:sort | xsl:with-param)* -->
</xsl:apply-templates>

The xsl:apply-templates instruction takes as input a sequence of items (typically nodes in a source tree), and produces as output a sequence of items; these will often be nodes to be added to a result tree.

If the instruction has one or more xsl:sort children, then the input sequence is sorted as described in 13 Sorting. The result of this sort is referred to below as the sorted sequence; if there are no xsl:sort elements, then the sorted sequence is the same as the input sequence.

Each item in the input sequence is processed by finding a template rule whose pattern matches that item. If there is more than one such template rule, the best among them is chosen, using rules described in 6.4 Conflict Resolution for Template Rules. If there is no template rule whose pattern matches the item, a built-in template rule is used (see 6.8 Built-in Template Rules). The chosen template rule is evaluated. The rule that matches the Nth item in the sorted sequence is evaluated with that item as the context item, with N as the context position, and with the length of the sorted sequence as the context size. Each template rule that is evaluated produces a sequence of items as its result. The resulting sequences (one for each item in the sorted sequence) are then concatenated, to form a single sequence. They are concatenated retaining the order of the items in the sorted sequence. The final concatenated sequence forms the result of the xsl:apply-templates instruction.

Example: Applying Template Rules

Suppose the source document is as follows:

<message>Proceed <emph>at once</emph> to the exit!</message>

This can be processed using the two template rules shown below.

<xsl:template match="message">
  <p>
    <xsl:apply-templates select="child::node()"/>
  </p>
</xsl:template>

<xsl:template match="emph">
  <b>
    <xsl:apply-templates select="child::node()"/>
  </b>
</xsl:template>

There is no template rule for the document node; the built-in template rule for this node will cause the message element to be processed. The template rule for the message element causes a p element to be written to the result tree; the contents of this p element are constructed as the result of the xsl:apply-templates instruction. This instruction selects the three child nodes of the message element (a text node containing the value "Proceed ", an emph element node, and a text node containing the value " to the exit!"). The two text nodes are processed using the built-in template rule for text nodes, which returns a copy of the text node. The emph element is processed using the explicit template rule that specifies match="emph".

When the emph element is processed, this template rule constructs a b element. The contents of the b element are constructed by means of another xsl:apply-templates instruction, which in this case selects a single node (the text node containing the value "at once"). This is again processed using the built-in template rule for text nodes, which returns a copy of the text node.

The final result of the match="message" template rule thus consists of a p element node with three children: a text node containing the value "Proceed ", a b element that is the parent of a text node containing the value "at once", and a text node containing the value " to the exit!". This result tree might be serialized as:

<p>Proceed <b>at once</b> to the exit!</p>

The default value of the select attribute is child::node(), which causes all the children of the context node to be processed.

[ERR XTTE0510] It is a type error if an xsl:apply-templates instruction with no select attribute is evaluated when the context item is not a node.

A select attribute can be used to process items selected by an expression instead of processing all children. The value of the select attribute is an expression.

Example: Applying Templates to Selected Nodes

The following example processes all of the given-name children of the author elements that are children of author-group:

<xsl:template match="author-group">
  <fo:wrapper>
    <xsl:apply-templates select="author/given-name"/>
  </fo:wrapper>
</xsl:template>

 

Example: Applying Templates to Nodes that are not Descendants

It is also possible to process elements that are not descendants of the context node. This example assumes that a department element has group children and employee descendants. It finds an employee's department and then processes the group children of the department.

<xsl:template match="employee">
  <fo:block>
    Employee <xsl:apply-templates select="name"/> belongs to group
    <xsl:apply-templates select="ancestor::department/group"/>
  </fo:block>
</xsl:template>

 

Example: Matching Nodes by Schema-Defined Types

It is possible to write template rules that are matched according to the schema-defined type of an element or attribute. The following example applies different formatting to the children of an element depending on their type:

<xsl:template match="product">
  <table>
    <xsl:apply-templates select="*"/>
  </table>
</xsl:template>

<xsl:template match="product/*" priority="3">
  <tr>
    <td><xsl:value-of select="name()"/></td>
    <td><xsl:next-match/></td>
  </tr>
</xsl:template>

<xsl:template match="product/element(*, xs:decimal) | 
                     product/element(*, xs:double)" priority="2">  
  <xsl:value-of select="format-number(xs:double(.), '#,###0.00')"/>
</xsl:template>

<xsl:template match="product/element(*, xs:date)" priority="2">
  <xsl:value-of select="format-date(., '[Mn] [D], [Y]')"/>
</xsl:template>

<xsl:template match="product/*" priority="1.5">
  <xsl:value-of select="."/>
</xsl:template>

The xsl:next-match instruction is described in 6.9 Overriding Template Rules.

 

Example: Re-ordering Elements in the Result Tree

Multiple xsl:apply-templates elements can be used within a single template to do simple reordering. The following example creates two HTML tables. The first table is filled with domestic sales while the second table is filled with foreign sales.

<xsl:template match="product">
  <table>
    <xsl:apply-templates select="sales/domestic"/>
  </table>
  <table>
    <xsl:apply-templates select="sales/foreign"/>
  </table>
</xsl:template>

 

Example: Processing Recursive Structures

It is possible for there to be two matching descendants where one is a descendant of the other. This case is not treated specially: both descendants will be processed as usual.

For example, given a source document

<doc><div><div></div></div></doc>

the rule

<xsl:template match="doc">
  <xsl:apply-templates select=".//div"/>
</xsl:template>

will process both the outer div and inner div elements.

This means that if the template rule for the div element processes its own children, then these grandchildren will be processed more than once, which is probably not what is required. The solution is to process one level at a time in a recursive descent, by using select="div" in place of select=".//div"

 

Example: Applying Templates to Atomic Values

This example reads a non-XML text file and processes it line-by-line, applying different template rules based on the content of each line:

<xsl:template name="main">
  <xsl:apply-templates select="unparsed-text-lines('input.txt')"/>
</xsl:template>

<xsl:template match=".[starts-with(., '==')]">
  <h2><xsl:value-of select="replace(., '==', '')"/></h2>
</xsl:template>

<xsl:template match=".[starts-with(., '::')]">
  <p class="indent"><xsl:value-of select="replace(., '::', '')"/></p>
</xsl:template>

<xsl:template match=".">
  <p class="body"><xsl:value-of select="."/></p>
</xsl:template>

Note:

The xsl:apply-templates instruction is most commonly used to process nodes that are descendants of the context node. Such use of xsl:apply-templates cannot result in non-terminating processing loops. However, when xsl:apply-templates is used to process elements that are not descendants of the context node, the possibility arises of non-terminating loops. For example,

<xsl:template match="foo">
  <xsl:apply-templates select="."/>
</xsl:template>

Implementations may be able to detect such loops in some cases, but the possibility exists that a stylesheet may enter a non-terminating loop that an implementation is unable to detect. This may present a denial of service security risk.

6.4 Conflict Resolution for Template Rules

It is possible for a selected item to match more than one template rule with a given mode M. When this happens, only one template rule is evaluated for the item. The template rule to be used is determined as follows:

  1. First, only the matching template rule or rules with the highest import precedence are considered. Other matching template rules with lower precedence are eliminated from consideration.

  2. Next, of the remaining matching rules, only those with the highest priority are considered. Other matching template rules with lower priority are eliminated from consideration.

    [Definition: The priority of a template rule is specified by the priority attribute on the xsl:template declaration. If no priority is specified explicitly for a template rule, its default priority is used, as defined in 6.5 Default Priority for Template Rules.]

    [ERR XTSE0530] The value of the priority attribute must conform to the rules for the xs:decimal type defined in [XML Schema Part 2]. Negative values are permitted.

  3. If this leaves more than one matching template rule, then:

    1. If the mode M has an xsl:mode declaration, and the attribute value on-multiple-match="fail" is specified in the mode declaration, a dynamic error is signaled. The error is treated as occurring in the xsl:apply-templates instruction, and can be recovered by wrapping that instruction in an xsl:try instruction.

      [ERR XTDE0540] It is a dynamic error if the conflict resolution algorithm for template rules leaves more than one matching template rule when the declaration of the relevant mode has an on-multiple-match attribute with the value fail.

    2. Otherwise, of the matching template rules that remain, the one that occurs last in declaration order is used.

    Note:

    This was a recoverable error in XSLT 2.0, meaning that it was implementation-defined whether the error was signaled, or whether the ambiguity was resolved by taking the last matching rule in declaration order. In XSLT 3.0 this situation is not an error unless the attribute value on-multiple-match="fail" is specified in the mode declaration. It is also possible to request warnings when this condition arises, by means of the attribute warning-on-multiple-match="yes".

6.5 Default Priority for Template Rules

[Definition: If no priority attribute is specified on an xsl:template element, a default priority is computed, based on the syntax of the pattern supplied in the match attribute.] The rules are as follows.

  1. If the top-level pattern is a ParenthesizedExprP then the outer parentheses are effectively stripped; these rules are applied recursively to the UnionExprP contained in the ParenthesizedExprP.

  2. If the top-level pattern is a UnionExprP consisting of multiple alternatives separated by | or union, then the template rule is treated equivalently to a set of template rules, one for each alternative. These template rules are adjacent to each other in declaration order, and the declaration order within this set of template rules (which affects the result of xsl:next-match if the alternatives have the same default priority) is the order of alternatives in the UnionExprP.

    Note:

    The splitting of a template rule into multiple rules occurs only if there is no explicit priority attribute.

  3. If the top-level pattern is a IntersectExceptExprP containing two or more PathExprP operands separated by intersect or except operators, then the priority of the pattern is that of the first PathExprP.

  4. If the pattern is a PredicatePattern then its priority is 1 (one), unless the PredicateList is empty, in which case the priority is −1 (minus one).

  5. If the pattern is a PathExprP taking the form /, then the priority is −0.5 (minus 0.5).

  6. If the pattern is a PathExprP taking the form of an EQName optionally preceded by a ForwardAxisP or has the form processing-instruction( StringLiteralXP30 ) or processing-instruction( NCNameNames ) optionally preceded by a ForwardAxisP, then the priority is 0 (zero).

  7. If the pattern is a PathExprP taking the form of an ElementTestXP30 or AttributeTestXP30, optionally preceded by a ForwardAxisP, then the priority is as shown in the table below. In this table, the symbols E, A, and T represent an arbitrary element name, attribute name, and type name respectively, while the symbol * represents itself. The presence or absence of the symbol ? following a type name does not affect the priority.

    Format Priority Notes
    element() −0.5 (equivalent to *)
    element(*) −0.5 (equivalent to *)
    attribute() −0.5 (equivalent to @*)
    attribute(*) −0.5 (equivalent to @*)
    element(E) 0 (equivalent to E)
    element(*,T) 0 (matches by type only)
    attribute(A) 0 (equivalent to @A)
    attribute(*,T) 0 (matches by type only)
    element(E,T) 0.25 (matches by name and type)
    schema-element(E) 0.25 (matches by substitution group and type)
    attribute(A,T) 0.25 (matches by name and type)
    schema-attribute(A) 0.25 (matches by name and type)
  8. If the pattern is a PathExprP taking the form of a DocumentTestXP30, then if it includes no ElementTestXP30 or SchemaElementTestXP30 the priority is −0.5. If it does include an ElementTestXP30 or SchemaElementTestXP30, then the priority is the same as the priority of that ElementTestXP30 or SchemaElementTestXP30, computed according to the table above.

  9. If the pattern is a PathExprP taking the form of an NCNameNames:* or *:NCNameNames, optionally preceded by a ForwardAxisP, then the priority is −0.25.

  10. If the pattern is a PathExprP taking the form of any other NodeTestXP30, optionally preceded by a ForwardAxisP, then the priority is −0.5.

  11. In all other cases, the priority is +0.5.

Note:

In many cases this means that highly selective patterns have higher priority than less selective patterns. The most common kind of pattern (a pattern that tests for a node of a particular kind, with a particular expanded QName or a particular type) has priority 0. The next less specific kind of pattern (a pattern that tests for a node of a particular kind and an expanded QName with a particular namespace URI) has priority −0.25. Patterns less specific than this (patterns that just test for nodes of a given kind) have priority −0.5. Patterns that specify both the name and the required type have a priority of +0.25, putting them above patterns that only specify the name or the type. Patterns more specific than this, for example patterns that include predicates or that specify the ancestry of the required node, have priority 0.5.

However, it is not invariably true that a more selective pattern has higher priority than a less selective pattern. For example, the priority of the pattern node()[self::*] is higher than that of the pattern salary. Similarly, the patterns attribute(*, xs:decimal) and attribute(*, xs:short) have the same priority, despite the fact that the latter pattern matches a subset of the nodes matched by the former. Therefore, to achieve clarity in a stylesheet it is good practice to allocate explicit priorities.

6.6 Modes

[Definition:  Modes allow a node in a source tree to be processed multiple times, each time producing a different result. They also allow different sets of template rules to be active when processing different trees, for example when processing documents loaded using the document function (see 20.1 fn:document) or when processing temporary trees.]

Modes are identified by an expanded QName; in addition to any named modes, there is always one unnamed mode available. Whether a mode is named or unnamed, its properties may be defined in an xsl:mode declaration. If a mode name is used (for example in an xsl:template declaration or an xsl:apply-templates instruction) and no declaration of that mode appears in the stylesheet, the mode is implicitly declared with default properties.

6.6.1 Declaring Modes

<!-- Category: declaration -->
<xsl:mode
  name? = eqname
  streamable? = "yes" | "no"
  on-no-match? = "deep-copy" | "shallow-copy" | "deep-skip" | "shallow-skip" | "text-only-copy" | "fail"
  on-multiple-match? = "use-last" | "fail"
  warning-on-no-match? = "yes" | "no"
  warning-on-multiple-match? = "yes" | "no"
  typed? = "yes" | "no" | "strict" | "lax" | "unspecified"
  visibility? = "public" | "private" | "final" >
  <!-- Content: (xsl:context-item?) -->
</xsl:mode>

[Definition: There is always an unnamed mode available. The unnamed mode is the default mode used when no mode attribute is specified on an xsl:apply-templates instruction or xsl:template declaration, unless a different default mode has been specified using the [xsl:]default-mode attribute of a containing element.]

Every mode other than the unnamed mode is identified by an expanded QName.

A stylesheet may contain multiple xsl:mode declarations and may include or import stylesheet modules that also contain xsl:mode declarations. The name of an xsl:mode declaration is the value of its name attribute, if any.

[Definition: All the xsl:mode declarations in a stylesheet that share the same name are grouped into a named mode definition; those that have no name are grouped into a single unnamed mode definition.]

If a stylesheet does not contain a declaration of the unnamed mode, a declaration is implied equivalent to an xsl:mode element with the single attribute initial="yes". Similarly, if there is a mode that is named in an xsl:template or xsl:apply-templates element, or in the [xsl:]default-mode attribute of a containing element, and the stylesheet does not contain a declaration of that mode, then a declaration is implied comprising an xsl:mode element with a name attribute plus the attribute initial="yes".

The contained xsl:context-item element, if present, is used to declare requirements for the initial context item when this mode is used as the initial mode. Therefore, there must be no xsl:context-item child if initial="no" is specified.

[ERR XTSE0542] It is a static error if an xsl:mode declaration specifying initial="no" contains an xsl:context-item element.

The attributes of the xsl:mode declaration establish values for a number of properties of a mode. The allowed values and meanings of the attributes are given in the following table.

Attribute Values Meaning
name A EQName Specifies the name of the mode. If omitted, this xsl:mode declaration provides properties of the unnamed mode
streamable yes or no (default no) Determines whether template rules in this mode are to be capable of being processed using streaming. If the value yes is specified, then the body of any template rule that uses this mode must conform to the rules for streamable templates given in 6.6.3 Streamable Templates.
on-no-match One of deep-copy, shallow-copy, deep-skip, shallow-skip, text-only-copy or fail (default text-only-copy) Determines selection of the built-in template rules that are used to process a node when an xsl:apply-templates instruction selects a node that does not match any user-written template rule in the stylesheet. For details, see 6.8 Built-in Template Rules.
on-multiple-match One of fail or use-last (default use-last) Defines the action to be taken when xsl:apply-templates is used in this mode and more than one user-written template rule is available to process the node, having the same import precedence and priority. The value fail indicates that it is a dynamic error if more than one template rule matches the node. The value use-last indicates that the situation is not to be treated as an error (the last template in declaration order is the one that is used).
warning-on-no-match One of yes or no. The default is implementation-defined Requests the processor to output (or not to output) a warning message in the case where an xsl:apply-templates instruction selects a node that matches no template rule. The form and destination of such warnings is implementation-defined. The processor may ignore this attribute, for example if the environment provides no suitable means of communicating with the user.
warning-on-multiple-match One of yes or no. The default is implementation-defined Requests the processor to output a warning message in the case where an xsl:apply-templates instruction selects a node that matches multiple template rules having the same import precedence and priority. The form and destination of such warnings is implementation-defined. The processor may ignore this attribute, for example if the environment provides no suitable means of communicating with the user.
typed One of yes, no, strict, lax, or unspecified. The default is unspecified. Informs the processor whether the nodes to be processed by template rules in this mode are to be typed or untyped. If the value yes is specified, then all nodes processed in this mode must be typed (a dynamic error occurs if xsl:apply-templates in this mode selects an element or attribute whose type annotation is xs:untyped or xs:untypedAtomic). If the value no is specified, then all nodes processed in this mode must be untyped (a dynamic error occurs if xsl:apply-templates in this mode selects an element or attribute whose type annotation is anything other than xs:untyped or xs:untypedAtomic). The value strict is equivalent to yes, with the additional provision that within the match pattern of every template rule in this mode, any NameTest used as an AbbrevForwardStep (with no preceding "@") in the ForwardStepP of the first StepExprP of a RelativePathExprP is interpreted as match="schema-element(product)", while match="product/code" is interpreted as match="schema-element(product)/code". The value lax is equivalent to strict, except that the interpretation of a NameTest as a SchemaElementTest occurs only if it matches the name of a global element declaration in the in-scope schema declarations. The value unspecified is equivalent to omitting the attribute, and places no constraints on whether the nodes to be processed in this mode are typed or untyped.
visibility One of public, private, or final. The default is private. See 3.6.2.2 Visibility of Declarations. A mode is not eligible to be used as the initial mode if its visibility is private.

[ERR XTTE3100] It is a type error if an xsl:apply-templates instruction in a particular mode selects an element or attribute whose type is xs:untyped or xs:untypedAtomic when the typed attribute of that mode specifies the value yes, strict, or lax.

[ERR XTTE3110] It is a type error if an xsl:apply-templates instruction in a particular mode selects an element or attribute whose type is anything other than xs:untyped or xs:untypedAtomic when the typed attribute of that mode specifies the value no.

[Definition: A streamable mode is a mode that is declared in an xsl:mode declaration with the attribute streamable="yes".]

For any named mode, the effective value of each attribute is taken from an xsl:mode declaration that has a matching name in its name attribute, and that specifies an explicit value for the required attribute. If there is more than one such declaration, the one with highest import precedence is used.

For the unnamed mode, the effective value of each attribute is taken from an xsl:mode declaration that has no name attribute, and that specifies an explicit value for the required attribute. If there is no such declaration, the default value of the attribute is used. If there is more than one such declaration, the one with highest import precedence is used.

The above rules apply both to the attributes (other than name) of the xsl:mode element itself, and to the attributes of the contained xsl:context-item element if present.

[ERR XTSE0545] It is a static error if a named or unnamed mode contains two conflicting values for the same attribute in different xsl:mode declarations having the same import precedence, unless there is another definition of the same attribute with higher import precedence. The attributes in question are the attributes other than name on the xsl:mode element, and the as attribute on the contained xsl:context-item element if present.

If the initial context item supplied to a stylesheet is a streamed document node, then it is not permitted for the values of global variables to be dependent on the context item in a way that requires reading of the input stream. This constraint is enforced by the following static rule:

[ERR XTSE0548] It is a static error if there is both (a) a mode definition in the stylesheet that has the effective attribute values streamable="yes" and initial="yes", and (b) a global variable in the stylesheet whose initializing expression is not motionless with respect to its context item, as defined in 19 Streamability.

6.6.2 Using Modes

A template rule is applicable to one or more modes. The modes to which it is applicable are defined by the mode attribute of the xsl:template element. If the attribute is omitted, then the template rule is applicable to the default mode specified in the [xsl:]default-mode attribute of the innermost containing element that has such an attribute, which in turn defaults to the unnamed mode. If the mode attribute is present, then its value must be a non-empty whitespace-separated list of tokens, each of which defines a mode to which the template rule is applicable. Each token must be one of the following:

  • an EQName, which is expanded as described in 5.1 Qualified Names to define the name of the mode

  • the token #default, to indicate that the template rule is applicable to the default mode that would apply if the mode attribute were absent

  • the token #unnamed, to indicate that the template rule is applicable to the unnamed mode

  • the token #all, to indicate that the template rule is applicable to all modes (specifically, to the unnamed mode and to every mode that is named explicitly or implicitly in an xsl:apply-templates instruction anywhere in the stylesheet).

[ERR XTSE0550] It is a static error if the list of modes is empty, if the same token is included more than once in the list, if the list contains an invalid token, or if the token #all appears together with any other value.

The xsl:apply-templates element also has an optional mode attribute. The value of this attribute must be one of the following:

If the attribute is omitted, the default mode for the stylesheet module is used.

When searching for a template rule to process each item selected by the xsl:apply-templates instruction, only those template rules that are applicable to the selected mode are considered.

[Definition: At any point in the processing of a stylesheet, there is a current mode. When the transformation is initiated, the current mode is the initial mode, as described in 2.3 Initiating a Transformation. Whenever an xsl:apply-templates instruction is evaluated, the current mode becomes the mode selected by this instruction.] When a non-contextual function call is made, the current mode is set to the unnamed mode. While evaluating global variables and parameters, and the sequence constructor contained in xsl:key or xsl:sort, the current mode is set to the unnamed mode. No other instruction changes the current mode. The current mode while evaluating an attribute set is the same as the current mode of the caller. On completion of the xsl:apply-templates instruction, or on return from a stylesheet function call, the current mode reverts to its previous value. The current mode is used when an xsl:apply-templates instruction uses the syntax mode="#current"; it is also used by the xsl:apply-imports and xsl:next-match instructions (see 6.9 Overriding Template Rules).

6.6.3 Streamable Templates

A template is guaranteed-streamable if and only if all the following conditions are satisfied:

Specifying streamable="yes" on an xsl:mode declaration declares an intent that every template rule that includes that mode (explicitly or implicitly, including by specifying #all), should be guaranteed streamable according to these criteria. The consequences of declaring the mode to be streamable when there is such a template rule that is not guaranteed streamable depend on the conformance level of the processor, and are explained in 19.10 Streamability Guarantees.

Processing of a document using streamable templates may be initiated using code such as the following, where S is a mode declared with streamable="yes":

<xsl:stream href="bigdoc.xml">
  <xsl:apply-templates mode="S"/>
</xsl:stream>

Alternatively, streamed processing may be initiated by invoking the transformation with an initial mode declared as streamable, while supplying the initial context item (in an implementation-defined way) as a streamed document.

Note:

Invoking a streamable template using the construct <xsl:apply-templates select="doc('bigdoc.xml')"/> does not ensure streamed processing. As always, processors may use streamed processing if they are able to do so, but when the docFO30 or document functions are used, processors are obliged to ensure that the results are deterministic, which may be difficult to reconcile with streaming (if the same document is read twice, the results must be identical). The use of xsl:stream does not offer the same guarantees of determinism.

For an example of processing a collection of documents by use of the function uri-collectionFO30 in conjunction with xsl:stream, see 18.1.2 Examples of xsl:stream .

6.7 Declaring the Context Item

The xsl:context-item element is used for two purposes:

<xsl:context-item
  as? = sequence-type
  use? = "required" | "optional" | "prohibited" />

If the as attribute is present then its value must be an ItemTypeXP30. If the attribute is omitted this is equivalent to specifying as="item()".

A type error is signaled if the supplied context item does not match its required type. The error code is the same as for xsl:param: [see ERR XTTE0590].

6.7.1 Declaring the Initial Context Item for a Mode

This section applies when xsl:context-item is used to declare the initial context item for a mode.

When the xsl:context-item element appears as a child of xsl:mode, the only permitted value for the use attribute is required, indicating that an initial context item must be supplied by the calling application when this mode is selected as the initial mode. The context item that is supplied will be converted to the declared type using the function conversion rules. This may result in a type error if the conversion is not possible.

Note:

If the ItemType is one that can only be satisfied by a schema-validated input document, for example as="schema-element(invoice)", the processor may interpret this as a request to apply schema validation to the input. Similarly, if the KindTest indicates that an element node is required, the processor may interpret this as a request to supply the document element rather than the document node of a supplied input document.

If there is no xsl:context-item element for an xsl:mode that specifies initial="yes", this is equivalent to specifying <xsl:context-item as="item()"/>

Example: Declaring the Required Context Item

The following example declares two modes, both of which have initial="yes" meaning that they can be used as entry points to the stylesheet. In the first mode, named invoice, the required context item is a schema-validated invoice element. In the second mode, named po, the required context item is a schema-validated purchase-order element. A third mode, format-address is declared with initial="no" so it cannot be used as an initial entry point; this mode might be used when processing content that is common to invoices and purchase orders.

<xsl:mode name="invoice" initial="yes" on-no-match="deep-copy">
  <xsl:context-item as="schema-element(invoice)"/>
</xsl:mode>
<xsl:mode name="po" initial="yes" on-no-match="deep-copy">
  <xsl:context-item as="schema-element(purchase-order)"/>
</xsl:mode>
<xsl:mode name="format-address" initial="no"/>

6.7.2 Declaring the context item for a template

The xsl:context-item element can appear as a child of xsl:template to define the type of the context item passed to a named template. If the named template is also the initial template, then this constrains the initial context item for the transformation as a whole.

If an xsl:context-item element is present as the first child element of xsl:template, it defines whether the template requires a context item to be supplied, and if so, what the type of the context item must be. If this template is the initial template, then this has the effect of placing constraints on the initial context item for the transformation as a whole.

The use attribute of xsl:context-item takes the value required, optional, or prohibited. If the value required is specified, then there must be a context item. (This will automatically be the case if the template is invoked using xsl:apply-templates, xsl:apply-imports, or xsl:next-match, but not if it is invoked using xsl:call-template). If the value optional is specified, or if the attribute is omitted, or if the xsl:context-item element is omitted, then there may or may not be a context item when the template is invoked. If the containing xsl:template element has no name attribute then the only permitted value is required. If the value prohibited is specified, then there will be no context item available to the body template (if the calling template has a context item, it will not be made available to the called template).

The as attribute of the xsl:context-item defines the required type of the context item supplied to the template if one is supplied. The default value is as="item()". If a context item is supplied (which will automatically be the case if the template is invoked using xsl:apply-templates, xsl:apply-imports, or xsl:next-match) then if will be converted to the required type by applying the function conversion rules; a type error [see ERR XTTE0590] occurs if conversion to the required type is not possible. The processor may signal a type error statically if the required context item type is incompatible with the match pattern, that is, if no item that satisfies the match pattern can also satisfy the required context item type.

The xsl:context-item element plays no part in deciding whether and when the template rule is invoked in response to an xsl:apply-templates instruction.

[ERR XTTE3090] It is a type error if the xsl:context-item child of xsl:template specifies that a context item is required and none is supplied by the caller, that is, if the context item is absent at the point where xsl:call-template is evaluated.

6.8 Built-in Template Rules

When an item is selected by xsl:apply-templates and there is no user-specified template rule in the stylesheet that can be used to process that item, then a built-in template rule is evaluated instead.

The built-in template rules have lower import precedence than all other template rules. Thus, the stylesheet author can override a built-in template rule by including an explicit template rule.

There are six sets of built-in template rules available. The set that is chosen is a property of the mode selected by the xsl:apply-templates instruction. This property is set using the on-no-match attribute of the xsl:mode declaration, which takes one of the six values deep-copy, shallow-copy, deep-skip, shallow-skip, text-only-copy, or fail, the default being text-only-copy. The effect of these six sets of built-in template rules is explained in the following subsections.

6.8.1 Built-in Templates: Text-only Copy

The effect of processing a tree using a mode that specifies on-no-match="text-only-copy" is that the textual content of the source document is retained while losing the markup, except where explicit template rules dictate otherwise. When an element is encountered for which there is no explicit template rule, the processing continues with the children of that element. Text nodes are copied to the output.

The built-in rule for document nodes and element nodes is equivalent to calling xsl:apply-templates with no select attribute, and with the mode attribute set to #current. If the built-in rule was invoked with parameters, those parameters are passed on in the implicit xsl:apply-templates instruction.

The built-in template rule for text and attribute nodes and atomic values returns a text node containing the string value of the context node. It is effectively:

<xsl:template match="text()|@*|xs:anyAtomicType" mode="M">
  <xsl:value-of select="string(.)"/>
</xsl:template>

Note:

This text node may have a string value that is zero-length.

The built-in template rule for processing instructions, comments, namespace nodes, and function items does nothing (it returns the empty sequence).

<xsl:template 
   match="processing-instruction()|comment()|namespace-node()|function(*)" 
   mode="M"/>
Example: Using a Built-In Template Rule

Suppose the stylesheet contains the following instruction:

<xsl:apply-templates select="title" mode="M">
  <xsl:with-param name="init" select="10"/>
</xsl:apply-templates>

If there is no explicit template rule that matches the title element, then the following implicit rule is used:

<xsl:template match="title" mode="M">
  <xsl:param name="init"/>
  <xsl:apply-templates mode="#current">
    <xsl:with-param name="init" select="$init"/>
  </xsl:apply-templates>
</xsl:template>

6.8.2 Built-in Templates: Deep Copy

The effect of processing a tree using a mode that specifies on-no-match="deep-copy" is that an unmatched element in the source tree is copied unchanged to the output, together with its entire subtree. Other unmatched items are also copied unchanged. The subtree is copied unconditionally, without attempting to match nodes in the subtree against template rules.

When this default action is selected for a mode M, all items (nodes, atomic values, and functions) are processed using a template rule that is equivalent to the following:

<xsl:template match="." mode="M">
  <xsl:copy-of select="." validation="preserve"/>
</xsl:template>

6.8.3 Built-in Templates: Shallow Copy

The effect of processing a tree using a mode that specifies on-no-match="shallow-copy" is that the source tree is copied unchanged to the output, except for nodes where different processing is specified using an explicit template rule.

When this default action is selected for a mode M, all items (nodes, atomic values, and functions) are processed using a template rule that is equivalent to the following, except that all parameters supplied in xsl:with-param elements are passed on implicitly to the called templates:

<xsl:template match="." mode="M">
  <xsl:copy validation="preserve">
    <xsl:apply-templates select="@*" mode="M"/>
    <xsl:apply-templates select="node()" mode="M"/>
  </xsl:copy>
</xsl:template>

This rule is often referred to as the identity template, though it should be noted that it does not preserve node identity.

Note:

This rule differs from the traditional identity template rule by using two xsl:apply-templates instructions, one to process the attributes and one to process the children. The only observable difference from the traditional select="node() | @* is that with two separate instructions, the value of position() in the called templates forms one sequence starting at 1 for the attributes, and a new sequence starting at 1 for the children.

A further reason for choosing this form is for streamability: this formulation is guaranteed-streamable, whereas the traditional form using select="node() | @*" is not (see 19.8.4.5 Streamability of xsl:apply-templates).

Example: Modified Identity Transformation

The following stylesheet transforms an input document by deleting all elements named note, together with their attributes and descendants:

<xsl:stylesheet version="3.0"
     xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
                                  
<xsl:mode on-no-match="shallow-copy" streamable="yes"/>

<xsl:template match="note">
  <!-- no action -->
</xsl:template>

</xsl:stylesheet>

6.8.4 Built-in Templates: Deep Skip

The effect of processing a tree using a mode that specifies on-no-match="deep-skip" is that where no explicit template rule is specified for an element, that element and all its descendants are ignored, and are not copied to the result tree.

The effect of choosing on-no-match="deep-skip" is as follows:

  • The built-in rule for document nodes is equivalent to calling xsl:apply-templates with no select attribute, and with the mode attribute set to #current. If the built-in rule was invoked with parameters, those parameters are passed on in the implicit xsl:apply-templates instruction.

  • The built-in rule for all items other than document nodes (that is, for all other kinds of node, as well as atomic values and functions) is to do nothing, that is, to return an empty sequence (without applying templates to any children or ancestors).

6.8.5 Built-in Templates: Shallow Skip

The effect of processing a tree using a mode that specifies on-no-match="shallow-skip" is to drop both the textual content and the markup from the result document, except where there is an explicit user-written template rule that dictates otherwise.

The built-in rule for document nodes and element nodes is the same as for on-no-match="text-only-copy": that is, it is equivalent to calling xsl:apply-templates with no select attribute, and with the mode attribute set to #current. If the built-in rule was invoked with parameters, those parameters are passed on in the implicit xsl:apply-templates instruction.

The built-in template rule for all other kinds of node, and for atomic values and functions, is empty: that is, when the item is matched, the built-in template rule returns an empty sequence.

6.8.6 Built-in Templates: Fail

The effect of choosing on-no-match="fail" for a mode is that every item selected in an xsl:apply-templates instruction must be matched by an explicit user-written template rule.

The built-in template rule is effectively:

<xsl:template match="." mode="M">
  <xsl:message terminate="yes" error-code="err:XTDE0555"/>
</xsl:template>

with an implementation-dependent message body.

[ERR XTDE0555] It is a dynamic error if xsl:apply-templates, xsl:apply-imports or xsl:next-match is used to process a node using a mode whose declaration specifies on-no-match="fail" when there is no template rule in the stylesheet whose match pattern matches that node.

6.9 Overriding Template Rules

<!-- Category: instruction -->
<xsl:apply-imports>
  <!-- Content: xsl:with-param* -->
</xsl:apply-imports>

<!-- Category: instruction -->
<xsl:next-match>
  <!-- Content: (xsl:with-param | xsl:fallback)* -->
</xsl:next-match>

A template rule that is being used to override another template rule (see 6.4 Conflict Resolution for Template Rules) can use the xsl:apply-imports or xsl:next-match instruction to invoke the overridden template rule. The xsl:apply-imports instruction only considers template rules in imported stylesheet modules; the xsl:next-match instruction considers all other template rules of lower import precedence and/or priority, and also declarations of the same precedence and priority that appear earlier in declaration order. Both instructions will invoke the built-in template rule for the context item (see 6.8 Built-in Template Rules) if no other template rule is found.

[Definition: At any point in the processing of a stylesheet, there may be a current template rule. Whenever a template rule is chosen as a result of evaluating xsl:apply-templates, xsl:apply-imports, or xsl:next-match, the template rule becomes the current template rule for the evaluation of the rule's sequence constructor. When an xsl:for-each, xsl:for-each-group, xsl:analyze-string, xsl:iterate, xsl:stream, xsl:merge, or xsl:evaluate instruction is evaluated, or when evaluating a sequence constructor contained in an xsl:sort or xsl:key element, or when a non-contextual function call is made, the current template rule becomes absent for the evaluation of that instruction or function.]

The current template rule is not affected by invoking named templates (see 10.1 Named Templates) or named attribute sets (see 10.2 Named Attribute Sets). While evaluating a global variable or the default value of a stylesheet parameter (see 9.5 Global Variables and Parameters) the current template rule is absent.

Note:

These rules ensure that when xsl:apply-imports or xsl:next-match is called, the context item is the same as when the current template rule was invoked.

Both xsl:apply-imports and xsl:next-match search for a template rule that matches the context item, and that is applicable to the current mode (see 6.6 Modes). In choosing a template rule, they use the usual criteria such as the priority and import precedence of the template rules, but they consider as candidates only a subset of the template rules in the stylesheet. This subset differs between the two instructions:

  • The xsl:apply-imports instruction considers as candidates only those template rules contained in stylesheet levels that are descendants in the import tree of the stylesheet level that contains the current template rule.

    Note:

    This is not the same as saying that the search considers all template rules whose import precedence is lower than that of the current template rule.

  • The xsl:next-match instruction considers as candidates all those template rules that come after the current template rule in the ordering of template rules implied by the conflict resolution rules given in 6.4 Conflict Resolution for Template Rules. That is, it considers all template rules with lower import precedence than the current template rule, plus the template rules that are at the same import precedence that have lower priority than the current template rule, plus the template rules with the same import precedence and priority that occur before the current template rule in declaration order.

    Note:

    As explained in 6.4 Conflict Resolution for Template Rules, a template rule with no priority attribute, whose match pattern contains multiple alternatives separated by |, is treated equivalently to a set of template rules, one for each alternative. This means that where the same item matches more than one alternative, it is possible for an xsl:next-match instruction to cause the current template rule to be invoked recursively. This situation does not occur when the template rule has an explicit priority.

If no matching template rule is found that satisfies these criteria, the built-in template rule for the context item is used (see 6.8 Built-in Template Rules).

An xsl:apply-imports or xsl:next-match instruction may use xsl:with-param child elements to pass parameters to the chosen template rule (see 9.10 Setting Parameter Values). It also passes on any tunnel parameters as described in 10.1.2 Tunnel Parameters.

[ERR XTDE0560] It is a dynamic error if xsl:apply-imports or xsl:next-match is evaluated when the current template rule is absent.

Example: Using xsl:apply-imports

For example, suppose the stylesheet doc.xsl contains a template rule for example elements:

<xsl:template match="example">
  <pre><xsl:apply-templates/></pre>
</xsl:template>

Another stylesheet could import doc.xsl and modify the treatment of example elements as follows:

<xsl:import href="doc.xsl"/>

<xsl:template match="example">
  <div style="border: solid red">
     <xsl:apply-imports/>
  </div>
</xsl:template>

The combined effect would be to transform an example into an element of the form:

<div style="border: solid red"><pre>...</pre></div>

An xsl:fallback instruction appearing as a child of an xsl:next-match instruction is ignored by an XSLT 2.0 or 3.0 processor, but can be used to define fallback behavior when the stylesheet is processed by an XSLT 1.0 processor with forwards compatible behavior.

6.10 Passing Parameters to Template Rules

A template rule may have parameters. The parameters are declared in the body of the template using xsl:param elements, as described in 9.2 Parameters.

Values for these parameters may be supplied in the calling xsl:apply-templates, xsl:apply-imports, or xsl:next-match instruction by means of xsl:with-param elements appearing as children of the calling instruction. The expanded QName represented by the name attribute of the xsl:with-param element must match the expanded QName represented by the name attribute of the corresponding xsl:param element.

[ERR XTDE0700] It is a dynamic error if a template that is invoked using xsl:apply-templates, xsl:apply-imports, or xsl:next-match declares a template parameter with required="yes" and no value for this parameter is supplied by the calling instruction. The same error is reported in the case of a tunnel parameter whether invoked using one of these three instructions or by xsl:call-template, as explained in 10.1.2 Tunnel Parameters.

It is not an error for these instructions to supply a parameter that does not match any parameter declared in the template rule that is invoked; unneeded parameter values are simply ignored.

A parameter may be declared as a tunnel parameter by specifying tunnel="yes" in the xsl:param declaration; in this case the caller must supply the value as a tunnel parameter by specifying tunnel="yes" in the corresponding xsl:with-param element. Tunnel parameters differ from ordinary template parameters in that they are passed transparently through multiple template invocations. They are fully described in 10.1.2 Tunnel Parameters.

7 Repetition

XSLT offers two constructs for processing each item of a sequence: xsl:for-each and xsl:iterate.

The main difference between the two constructs is that with xsl:for-each, the processing applied to each item in the sequence is independent of the processing applied to any other item; this means that the items may be processed in any order or in parallel, though the order of the output sequence is well defined and corresponds to the order of the input (sorted if so requested). By contrast, with xsl:iterate, the processing is explicitly sequential: while one item is being processed, values may be computed which are then available for use while the next item is being processed. This makes xsl:iterate suitable for tasks such as creating a running total over a sequence of financial transactions.

A further difference is that xsl:for-each permits sorting of the input sequence, while xsl:iterate does not.

7.1 The xsl:for-each instruction

<!-- Category: instruction -->
<xsl:for-each
  select = expression >
  <!-- Content: (xsl:sort*, sequence-constructor) -->
</xsl:for-each>

The xsl:for-each instruction processes each item in a sequence of items, evaluating the sequence constructor within the xsl:for-each instruction once for each item in that sequence.

The select attribute is required; it contains an expression which is evaluated to produce a sequence, called the input sequence. If there is an xsl:sort element present (see 13 Sorting) the input sequence is sorted to produce a sorted sequence. Otherwise, the sorted sequence is the same as the input sequence.

The xsl:for-each instruction contains a sequence constructor. The sequence constructor is evaluated once for each item in the sorted sequence, with the focus set as follows:

  • The context item is the item being processed.

  • The context position is the position of this item in the sorted sequence.

  • The context size is the size of the sorted sequence (which is the same as the size of the input sequence).

For each item in the input sequence, evaluating the sequence constructor produces a sequence of items (see 5.8 Sequence Constructors). These output sequences are concatenated; if item Q follows item P in the sorted sequence, then the result of evaluating the sequence constructor with Q as the context item is concatenated after the result of evaluating the sequence constructor with P as the context item. The result of the xsl:for-each instruction is the concatenated sequence of items.

Example: Using xsl:for-each

For example, given an XML document with this structure

<customers>
  <customer>
    <name>...</name>
    <order>...</order>
    <order>...</order>
  </customer>
  <customer>
    <name>...</name>
    <order>...</order>
    <order>...</order>
  </customer>
</customers>

the following would create an HTML document containing a table with a row for each customer element

<xsl:template match="/">
  <html>
    <head>
      <title>Customers</title>
    </head>
    <body>
      <table>
        <tbody>
          <xsl:for-each select="customers/customer">
            <tr>
              <th>
                <xsl:apply-templates select="name"/>
              </th>
              <xsl:for-each select="order">
                <td>
                  <xsl:apply-templates/>
                </td>
              </xsl:for-each>
            </tr>
          </xsl:for-each>
        </tbody>
      </table>
    </body>
  </html>
</xsl:template>

7.2 The xsl:iterate Instruction

<!-- Category: instruction -->
<xsl:iterate
  select = expression >
  <!-- Content: (xsl:param*, sequence-constructor, xsl:on-completion?) -->
</xsl:iterate>

<!-- Category: instruction -->
<xsl:next-iteration>
  <!-- Content: (xsl:with-param*) -->
</xsl:next-iteration>

<!-- Category: instruction -->
<xsl:break
  select? = expression >
  <!-- Content: (sequence-constructor) -->
</xsl:break>

<xsl:on-completion
  select? = expression >
  <!-- Content: (sequence-constructor) -->
</xsl:on-completion>

The select attribute is required; it contains an expression which is evaluated to produce a sequence, called the input sequence.

The sequence constructor contained in the xsl:iterate instruction is evaluated once for each item in the input sequence, in order, or until the loop exits by evaluating an xsl:break instruction, whichever is earlier. Within the sequence constructor that forms the body of the xsl:iterate instruction, the context item is set to each item from the value of the select expression in turn; the context position reflects the position of this item in the input sequence, and the context size is the number of items in the input sequence (which may be greater than the number of iterations, if the loop exits prematurely using xsl:break).

Note:

If xsl:iterate is used in conjunction with xsl:stream to achieve streaming, calls on the function lastFO30 will be disallowed.

The xsl:break and xsl:on-completion elements may have either a select attribute or a non-empty contained sequence constructor but not both. The effect of the element in both cases is obtained by evaluating the select expression if present or the contained sequence constructor otherwise; if neither is present, the value is an empty sequence.

The effect of xsl:next-iteration is to cause the iteration to continue by processing the next item in the input sequence, potentially with different values for the iteration parameters. The effect of xsl:break is to cause the iteration to finish, whether or not all the items in the input sequence have been processed. In both cases the affected iteration is the one controlled by the innermost ancestor xsl:iterate element.

The instructions xsl:next-iteration and xsl:break are allowed only as descendants of an xsl:iterate instruction, and only in a tail position within the sequence constructor forming the body of the xsl:iterate instruction.

[Definition: An instruction J is in a tail position within a sequence constructor SC if it satisfies one of the following conditions:]

[ERR XTSE3120] It is a static error if an xsl:break or xsl:next-iteration element appears other than in a tail position within the sequence constructor forming the body of an xsl:iterate instruction.

[ERR XTSE3125] It is a static error if the select attribute of xsl:break or xsl:on-completion is present and the instruction has children.

[ERR XTSE3130] It is a static error if the name attribute of an xsl:with-param child of an xsl:next-iteration element does not match the name attribute of an xsl:param child of the innermost containing xsl:iterate instruction.

Parameter names in xsl:with-param must be unique: [see ERR XTSE0670].

The result of the xsl:iterate instruction is the concatenation of the sequences that result from the repeated evaluation of the contained sequence constructor, followed by the sequence that results from evaluating the xsl:break or xsl:on-completion element if any.

Any xsl:param element that appears as a child of xsl:iterate declares a parameter whose value may vary from one iteration to the next. The initial value of the parameter is the value obtained according to the rules given in 9.3 Values of Variables and Parameters. The dynamic context for evaluating the initial value of an xsl:param element is the same as the dynamic context for evaluating the select expression of the xsl:iterate instruction (the context item is thus not the first item in the input sequence).

On the first iteration a parameter always takes its initial value (which may depend on variables or other aspects of the dynamic context). Subsequently:

  • If an xsl:next-iteration instruction is evaluated, then parameter values for processing the next item in the input sequence can be set in the xsl:with-param children of that instruction; in the absence of an xsl:with-param element that names a particular parameter, that parameter will retain its value from the previous iteration.

  • If an xsl:break instruction is evaluated, no further items in the input sequence are processed.

  • If neither an xsl:next-iteration nor an xsl:break instruction is evaluated, then the next item in the input sequence is processed using parameter values that are unchanged from the previous iteration.

The xsl:next-iteration instruction contributes nothing to the result sequence (technically, it returns an empty sequence). The instruction supplies parameter values for the next iteration, which are evaluated according to the rules given in 9.10 Setting Parameter Values; if there are no further items in the input sequence then it supplies parameter values for use while evaluating the body of the xsl:on-completion element if any.

The xsl:break instruction indicates that the iteration should terminate without processing any remaining items from the input sequence. The select expression or contained sequence constructor is evaluated using the same context item, position, and size as the xsl:break instruction itself, and the result is appended to the result of the xsl:iterate instruction as a whole.

If neither an xsl:next-iteration nor an xsl:break instruction is evaluated, the next item in the input sequence is processed with parameter values unchanged from the previous iteration; if there are no further items in the input sequence, the iteration terminates.

The optional xsl:on-completion element (which is not technically an instruction and is not technically part of the sequence constructor) is evaluated when the input sequence is exhausted. It is not evaluated if the evaluation is terminated using xsl:break. During evaluation of this sequence constructor the context item, position, and size are absent (that is, any reference to these values is an error). However, the values of the parameters to xsl:iterate are available, and take the values supplied by the xsl:next-iteration instruction evaluated while processing the last item in the sequence.

If the input sequence is empty, then the result of the xsl:iterate instruction is the result of evaluating the sequence constructor forming the body of the xsl:on-completion element, using the initial values of the xsl:param elements. If there is no xsl:on-completion element, the result is an empty sequence.

Note:

Conceptually, xsl:iterate behaves like a tail-recursive function. The xsl:next-iteration instruction then represents the recursive call, supplying the tail of the input sequence as an implicit parameter. There are two main reasons for providing the xsl:iterate instruction. One is that many XSLT users find writing recursive functions to be a difficult skill, and this construct promises to be easier to learn. The other is that recursive function calls are difficult for an optimizer to analyze. Because xsl:iterate is more constrained than a general-purpose head-tail recursive function, it should be more amenable to optimization. In particular, when the instruction is used in conjunction with xsl:stream, it is designed to make it easy for the implementation to use streaming techniques, processing the nodes in an input document sequentially as they are read, without building the entire document tree in memory.

The examples below use xsl:iterate in conjunction with the xsl:stream instruction. This is not the only way of using xsl:iterate, but it illustrates the way in which the two features can be combined to achieve streaming of a large input document.

Example: Using xsl:iterate to Compute Cumulative Totals

Suppose that the input XML document has this structure

<transactions>
  <transaction date="2008-09-01" value="12.00"/>
  <transaction date="2008-09-01" value="8.00"/>
  <transaction date="2008-09-02" value="-2.00"/>
  <transaction date="2008-09-02" value="5.00"/>
</transactions>

and that the requirement is to transform this to:

<account>
  <balance date="2008-09-01" value="12.00"/>
  <balance date="2008-09-01" value="20.00"/>
  <balance date="2008-09-02" value="18.00"/>
  <balance date="2008-09-02" value="23.00"/>
</account>

This can be achieved using the following code, which is designed to process the transaction file using streaming:

<account>
  <xsl:stream href="transactions.xml">
    <xsl:iterate select="transactions/transaction">
      <xsl:param name="balance" select="0.00" as="xs:decimal"/>
      <xsl:variable name="newBalance" 
                    select="$balance + xs:decimal(@value)"/>
      <balance date="{@date}" value="{$newBalance}"/>
      <xsl:next-iteration>
        <xsl:with-param name="balance" select="$newBalance"/>
      </xsl:next-iteration>
    </xsl:iterate>
  </xsl:stream>
</account>

The following example modifies this by only outputting the information for the first day's transactions:

<account>
  <xsl:stream href="'transactions.xml">
    <xsl:iterate select="transactions/transaction">
      <xsl:param name="balance" select="0.00" as="xs:decimal"/>
      <xsl:param name="prevDate" select="()" as="xs:date?"/>
      <xsl:variable name="newBalance" 
                    select="$balance + xs:decimal(@value)"/>
      <xsl:variable name="thisDate" 
                    select="xs:date(@date)"/>
      <xsl:choose>
        <xsl:when test="empty($prevDate) or $thisDate eq $prevDate">
          <balance date="{$thisDate}" 
                   value="{format-number($newBalance, '0.00')}"/>
          <xsl:next-iteration>
            <xsl:with-param name="balance" select="$newBalance"/>
            <xsl:with-param name="prevDate" select="$thisDate"/>
          </xsl:next-iteration>
        </xsl:when>
        <xsl:otherwise>
          <xsl:break/>
        </xsl:otherwise>
      </xsl:choose>
    </xsl:iterate>
  </xsl:stream>
</account>

The following code outputs the balance only at the end of each day, together with the final balance:

<account>
  <xsl:stream href="transactions.xml">
    <xsl:iterate select="transactions/transaction">
      <xsl:param name="balance" select="0.00" as="xs:decimal"/>
      <xsl:param name="prevDate" select="()" as="xs:date?"/>
      <xsl:variable name="newBalance" 
                    select="$balance + xs:decimal(@value)"/>
      <xsl:variable name="thisDate" select="xs:date(@date)"/>
      <xsl:if test="exists($prevDate) and $thisDate ne $prevDate">
        <balance date="{$prevDate}" 
                 value="{format-number($balance, '0.00')}"/>
      </xsl:if>
      <xsl:next-iteration>
        <xsl:with-param name="balance" select="$newBalance"/>
        <xsl:with-param name="prevDate" select="$thisDate"/>
      </xsl:next-iteration>
      <xsl:on-completion>
        <balance date="{$prevDate}" 
                 value="{format-number($balance, '0.00')}"/>
      </xsl:on-completion>
    </xsl:iterate>
  </xsl:stream>
</account>

If the sequence of transactions is empty, this code outputs a single element: <balance date="" value="0.00"/>.

 

Example: Collecting Multiple Values in a Single Pass

Problem: Given a sequence of employee elements, find the employees having the highest and lowest salary, while processing each employee only once.

Solution:

<xsl:stream href="employees.xml">
  <xsl:iterate select="employees/employee">
    <xsl:param name="highest" as="element(employee)*"/>
    <xsl:param name="lowest" as="element(employee)*"/>
    <xsl:variable name="is-new-highest" as="xs:boolean"
                  select="empty($highest[@salary ge current()/@salary])"/>
    <xsl:variable name="is-equal-highest" as="xs:boolean" 
                  select="exists($highest[@salary eq current()/@salary])"/> 
    <xsl:variable name="is-new-lowest" as="xs:boolean" 
                  select="empty($lowest[@salary le current()/@salary])"/>
    <xsl:variable name="is-equal-lowest" as="xs:boolean" 
                  select="exists($lowest[@salary eq current()/@salary])"/> 
    <xsl:variable name="new-highest-set" as="element(employee)*"
                  select="if ($is-new-highest) then .
                          else if ($is-equal-highest) then ($highest, .)
                          else $highest"/>
    <xsl:variable name="new-lowest-set" as="element(employee)*"
                  select="if ($is-new-lowest) then .
                          else if ($is-equal-lowest) then ($lowest, .)
                          else $lowest"/>
    <xsl:next-iteration>
      <xsl:with-param name="highest" select="$new-highest-set"/>
      <xsl:with-param name="lowest" select="$new-lowest-set"/>
    </xsl:next-iteration>
    <xsl:on-completion>
      <highest-paid-employees>
        <xsl:value-of select="$highest/name"/>
      </highest-paid-employees>
      <lowest-paid-employees>
        <xsl:value-of select="$lowest/name"/>
      </lowest-paid-employees>  
    </xsl:on-completion>
   </xsl:iterate>
 </xsl:stream>

If the input sequence is empty, this code outputs an empty highest-paid-employees element and an empty lowest-paid-employees element.

 

Example: Processing the Last Item in a Sequence Specially

When streaming, some limited look-ahead is needed to determine whether the item being processed is the last in a sequence. The lastFO30 function cannot be used in guaranteed-streamable code. The xsl:iterate instruction provides a solution to this problem.

Problem: render the last paragraph in a section in some special way, for example by using bold face. (The actual rendition is achieved by processing the paragraph with mode last-para.)

The solution uses xsl:iterate together with the copy-of function to maintain a one-element lookahead by explicit coding:

<xsl:template match="section" mode="streaming">
   <xsl:iterate select="para">
     <xsl:param name="prev" select="()" as="element(para)?"/>
     <xsl:if test="$prev">
       <xsl:apply-templates select="$prev"/>
     </xsl:if>
     <xsl:next-iteration>
       <xsl:with-param name="prev" select="copy-of(.)"/>
     </xsl:next-iteration>
     <xsl:on-completion>
       <xsl:apply-templates select="$prev" mode="last-para"/>      
     </xsl:on-completion>
   </xsl:iterate>
 </xsl:template>

8 Conditional Processing

There are two instructions in XSLT that support conditional processing: xsl:if and xsl:choose. The xsl:if instruction provides simple if-then conditionality; the xsl:choose instruction supports selection of one choice when there are several possibilities.

XSLT 3.0 also supports xsl:try and xsl:catch which define conditional processing to handle dynamic errors.

8.1 Conditional Processing with xsl:if

<!-- Category: instruction -->
<xsl:if
  test = expression >
  <!-- Content: sequence-constructor -->
</xsl:if>

The xsl:if element has a mandatory test attribute, which specifies an expression. The content is a sequence constructor.

The result of the xsl:if instruction depends on the effective boolean valueXP30 of the expression in the test attribute. The rules for determining the effective boolean value of an expression are given in [XPath 3.0]: they are the same as the rules used for XPath conditional expressions.

If the effective boolean value of the expression is true, then the sequence constructor is evaluated (see 5.8 Sequence Constructors), and the resulting sequence is returned as the result of the xsl:if instruction; otherwise, the sequence constructor is not evaluated, and the empty sequence is returned.

Example: Using xsl:if

In the following example, the names in a group of names are formatted as a comma separated list:

<xsl:template match="namelist/name">
  <xsl:apply-templates/>
  <xsl:if test="not(position()=last())">, </xsl:if>
</xsl:template>

The following colors every other table row yellow:

<xsl:template match="item">
  <tr>
    <xsl:if test="position() mod 2 = 0">
       <xsl:attribute name="bgcolor">yellow</xsl:attribute>
    </xsl:if>
    <xsl:apply-templates/>
  </tr>
</xsl:template>

8.2 Conditional Processing with xsl:choose

<!-- Category: instruction -->
<xsl:choose>
  <!-- Content: (xsl:when+, xsl:otherwise?) -->
</xsl:choose>

<xsl:when
  test = expression >
  <!-- Content: sequence-constructor -->
</xsl:when>

<xsl:otherwise>
  <!-- Content: sequence-constructor -->
</xsl:otherwise>

The xsl:choose element selects one among a number of possible alternatives. It consists of a sequence of one or more xsl:when elements followed by an optional xsl:otherwise element. Each xsl:when element has a single attribute, test, which specifies an expression. The content of the xsl:when and xsl:otherwise elements is a sequence constructor.

When an xsl:choose element is processed, each of the xsl:when elements is tested in turn (that is, in the order that the elements appear in the stylesheet), until one of the xsl:when elements is satisfied. If none of the xsl:when elements is satisfied, then the xsl:otherwise element is considered, as described below.

An xsl:when element is satisfied if the effective boolean valueXP30 of the expression in its test attribute is true. The rules for determining the effective boolean value of an expression are given in [XPath 3.0]: they are the same as the rules used for XPath conditional expressions.

The content of the first, and only the first, xsl:when element that is satisfied is evaluated, and the resulting sequence is returned as the result of the xsl:choose instruction. If no xsl:when element is satisfied, the content of the xsl:otherwise element is evaluated, and the resulting sequence is returned as the result of the xsl:choose instruction. If no xsl:when element is satisfied, and no xsl:otherwise element is present, the result of the xsl:choose instruction is an empty sequence.

Only the sequence constructor of the selected xsl:when or xsl:otherwise instruction is evaluated. The test expressions for xsl:when instructions after the selected one are not evaluated.

Example: Using xsl:choose

The following example enumerates items in an ordered list using arabic numerals, letters, or roman numerals depending on the depth to which the ordered lists are nested.

<xsl:template match="orderedlist/listitem">
  <fo:list-item indent-start='2pi'>
    <fo:list-item-label>
      <xsl:variable name="level"
                    select="count(ancestor::orderedlist) mod 3"/>
      <xsl:choose>
        <xsl:when test='$level=1'>
          <xsl:number format="i"/>
        </xsl:when>
        <xsl:when test='$level=2'>
          <xsl:number format="a"/>
        </xsl:when>
        <xsl:otherwise>
          <xsl:number format="1"/>
        </xsl:otherwise>
      </xsl:choose>
      <xsl:text>. </xsl:text>
    </fo:list-item-label>
    <fo:list-item-body>
      <xsl:apply-templates/>
    </fo:list-item-body>
  </fo:list-item>
</xsl:template>

8.3 Try/Catch

The xsl:try instruction can be used to trap dynamic errors occurring within the expression it wraps; the recovery action if such errors occur is defined using a child xsl:catch element.

<!-- Category: instruction -->
<xsl:try
  select? = expression >
  <!-- Content: (sequence-constructor, xsl:catch, (xsl:catch | xsl:fallback)*) -->
</xsl:try>

Note:

Because a sequence constructor may contain an xsl:fallback element, the effect of this content model is that an xsl:fallback instruction may appear as a child of xsl:try in any position.

<xsl:catch
  errors? = tokens
  select? = expression >
  <!-- Content: sequence-constructor -->
</xsl:catch>

An xsl:try instruction evaluates either the expression contained in its select attribute, or its contained sequence constructor, and returns the result of that evaluation if it succeeds without error. If a dynamic error occurs during the evaluation, the processor evaluates the first xsl:catch child element applicable to the error, and returns that result instead.

If the xsl:try element has a select attribute, then it must have no children other than xsl:catch and xsl:fallback. That is, the select attribute and the contained sequence constructor are mutually exclusive. If neither is present, the result of the xsl:try is an empty sequence (no dynamic error can occur in this case).

[ERR XTSE3140] It is a static error if the select attribute of the xsl:try element is present and the element has children other than xsl:catch and xsl:fallback elements.

Any xsl:fallback children of the xsl:try element are ignored by an XSLT 3.0 processor, but can be used to define the recovery action taken by an XSLT 1.0 or XSLT 2.0 processor operating with forwards compatible behavior.

The xsl:catch element has an optional errors attribute, which lists the error conditions that the xsl:catch element is designed to intercept. The default value is errors="*", which catches all errors. The value is a whitespace-separated list of NameTestsXP30; an xsl:catch element catches an error condition if this list includes a NameTest that matches the error code associated with that error condition.

Note:

Error codes are QNames. Those defined in this specification and in related specifications are all in the standard error namespace, and may therefore be caught using an xsl:catch element such as <xsl:catch errors="err:FODC0001 err:FODC0005"> where the namespace prefix err is bound to this namespace. Errors defined by implementors, and errors raised by an explicit call of the errorFO30 function or by use of the xsl:message or xsl:assert instruction, may use error codes in other namespaces.

If more than one xsl:catch element matches an error, the error is processed using the first one that matches, in document order. If no xsl:catch matches the error, then the error is not caught (that is, evaluation of the xsl:try element fails with the dynamic error).

An xsl:catch element may have either a select attribute, or a contained sequence constructor.

[ERR XTSE3150] It is a static error if the select attribute of the xsl:catch element is present unless the element has empty content.

The result of evaluating the xsl:catch element is the result of evaluating the XPath expression in its select attribute or the result of evaluating the contained sequence constructor; if neither is present, the result is an empty sequence. This result is delivered as the result of the xsl:try instruction.

If a dynamic error occurs during the evaluation of xsl:catch, it causes the containing xsl:try to fail with this error. The error is not caught by other sibling xsl:catch elements within the same xsl:try instruction, but it may be caught by an xsl:try instruction at an outer level, or by an xsl:try instruction nested within the xsl:catch.

Within the select expression, or within the sequence constructor contained by the xsl:catch element, a number of variables are implicitly declared, giving information about the error that occurred. These are lexically scoped to the xsl:catch element. These variables are all in the standard error namespace, and they are initialized as described in the following table:

Variable Type Value
err:code xs:QName The error code
err:description xs:string? A description of the error condition; an empty sequence if no description is available (for example, if the errorFO30 function was called with one argument).
err:value item()* Value associated with the error. For an error raised by calling the errorFO30 function, this is the value of the third argument (if supplied). For an error raised by evaluating xsl:message with terminate="yes", or a failing xsl:assert, this is the document node at the root of the tree containing the XML message body.
err:module xs:string? The URI (or system ID) of the stylesheet module containing the instruction where the error occurred; an empty sequence if the information is not available.
err:line-number xs:integer? The line number within the stylesheet module of the instruction where the error occurred; an empty sequence if the information is not available. The value may be approximate.
err:column-number xs:integer? The column number within the stylesheet module of the instruction where the error occurred; an empty sequence if the information is not available. The value may be approximate.

Variables declared within the sequence constructor of the xsl:try element (and not within an xsl:catch) are not visible within the xsl:catch element.

Note:

Within an xsl:catch it is possible to re-throw the error using the function call error($err:code, $err:description, $err:value).

The following additional rules apply to the catching of errors:

  1. All dynamic errors occurring during the evaluation of the xsl:try sequence constructor or select expression are caught (provided they match one of the xsl:catch elements).

    • This includes errors occurring in functions or templates invoked in the course of this evaluation, unless already caught by a nested xsl:try.

    • It also includes errors caused by calling the errorFO30 function, or the xsl:message instruction with terminate="yes", or the xsl:assert instruction.

    • It does not include errors that occur while evaluating references to variables whose declaration and initialization is outside the xsl:try.

  2. The existence of an xsl:try instruction does not affect the obligation of the processor to signal certain errors as static errors, or its right to choose whether to signal some errors (such as type errors) statically or dynamically. Static errors are never caught.

  3. Some fatal errors arising in the processing environment, such as running out of memory, may cause termination of the transformation despite the presence of an xsl:try instruction. This is implementation-dependent.

  4. If the sequence constructor or select expression of the xsl:try causes execution of xsl:result-document, xsl:message, or xsl:assert instructions and fails with a dynamic error that is caught, it is implementation-dependent whether these instructions have any externally visible effect. The processor is not required to roll back any changes made by these instructions. The same applies to any side effects caused by extension functions or extension instructions.

  5. A serialization error that occurs during the serialization of a final result tree produced using xsl:result-document is treated as a dynamic error in the evaluation of the xsl:result-document instruction, and may be caught by a containing xsl:try instruction. A serialization error that occurs while serializing the implicit final result tree returned by the initial template is treated as occurring after the transformation has finished, and cannot be caught.

  6. A validation error is treated as occurring in the instruction that requested validation. For example, if the stylesheet is producing XHTML output and requests validation of the entire result document by means of the attribute validation="strict" on the instruction that creates the outermost html element, then a validation failure can be caught only at that level. Although the validation error might be detected, for example, while writing a p element at a location where no p element is allowed, it is not treated as an error in the instruction that writes the p element and cannot be caught at that level.

  7. A type error may be caught if the processor raises it dynamically; this does not affect the processor's right to raise the error statically if it chooses.

    The following rules are provided to define which expression is considered to fail when a type error occurs, and therefore where the error can be caught. The general principle is that where the semantics of a construct C place requirements on the type of some subexpression, a type error is an error in the evaluation of C, not in the evaluation of the subexpression.

    For example, consider the following construct:

    <xsl:variable name="v" as="xs:integer">
      <xsl:sequence select="$foo"/>
    </xsl:variable>
    

    The expected type of the result of the sequence constructor is xs:integer; if the value of variable $foo turns out to be a string, then a type error will occur. It is not possible to catch this by writing:

    <xsl:variable name="v" as="xs:integer">
      <xsl:try>
        <xsl:sequence select="$foo"/>
        <xsl:catch>...</xsl:catch>
      </xsl:try>
    </xsl:variable>
    

    This fails to catch the error because the xsl:sequence instruction is deemed to evaluate successfully; the failure only occurs when the result of this instruction is bound to the variable.

    A similar rule applies to functions: if the body of a function computes a result which does not conform to the required type of the function result, it is not possible to catch this error within the function body itself; it can only be caught by the caller of the function. Similarly, if an expression used to compute an argument to a function returns a value of the wrong type for the function signature, this is not considered an error in this expression, but an error in evaluating the function call as a whole.

    A consequence of these rules is that when a type error occurs while initializing a global variable (because the initializer returns a value of the wrong type, given the declared type of the variable), then this error cannot be caught.

    Note:

    Because processors are permitted to report type errors during static analysis, it is unwise to attempt to recover from type errors dynamically. The best strategy is generally to prevent their occurrence. For example, rather than writing $p + 1 where $p is a parameter of unknown type, and then catching the type error that occurs if $p is not numeric, it is better first to test whether $p is numeric, perhaps by means of an expression such as $p instance of my:numeric, where my:numeric is a union type with xs:double, xs:float, and xs:decimal as its member types.

  8. The fact that the application tries to catch errors does not prevent the processor from organizing the evaluation in such a way as to prevent errors occurring. For example exists(//a[10 div . gt 5]) may still do an "early exit", rather than examining every item in the sequence just to see if it triggers a divide-by-zero error.

  9. Except as specified above, the optimizer must not rearrange the evaluation (at compile time or at run time) so that expressions written to be subject to the try/catch are evaluated outside its scope, or expressions written to be external to the try/catch are evaluated within its scope. This does not prevent expressions being rearranged, but any expression that is so rearranged must carry its try/catch context with it.

Note:

If an error occurs while evaluating an instruction within xsl:try, then no instruction within the xsl:try has any effect on the result returned by the xsl:try instruction. This means that if a processor is streaming the output to a serializer, it needs to adopt a strategy such as buffering the output in memory so that nothing is written until successful completion of the xsl:try instruction, or checkpointing the output so it can be rolled back when an error occurs.

Note:

Use of try/catch may affect the ability of a processor to perform streamed evaluation of a stylesheet. If the sequence constructor contained within xsl:try creates a sequence of ten elements, and these form part of a final result tree, then if a failure occurs while writing the tenth element, the work of creating the previous nine must be "undone". In effect this means that either the processor must delay sending the new elements to the serializer until it is assured of success, or the serializer must provide a mechanism to roll back elements already written.

8.3.1 Try/Catch Examples

Example: Catching a Divide-by-Zero Error

The following example divides an employee's salary by the number of years they have served, catching the divide-by-zero error if the latter is zero.

<xsl:try select="salary div length-of-service">
  <xsl:catch errors="err:FAOR0001" select="()"/>
</xsl:try>

 

Example: Catching an Error during Result-tree Validation

The following example generates a result tree and performs schema validation, outputting a warning message and serializing the invalid tree if validation fails.

<xsl:result-document href="out.xml">
  <xsl:variable name="result">
    <xsl:call-template name="construct-output"/>
  </xsl:variable>
  <xsl:try>
    <xsl:copy-of select="$result" validation="strict"/>
    <xsl:catch>
      <xsl:message>Warning: validation of result document failed:
          Error code: <xsl:value-of select="$err:code"/>
          Reason: <xsl:value-of select="$err:description"/>
      </xsl:message>
      <xsl:sequence select="$result"/>
    </xsl:catch>
  </xsl:try>
</xsl:result-document>

The reason that the result tree is constructed in a variable in this example is so that the unvalidated tree is available to be used within the xsl:catch element. An alternative approach would be to repeat the logic for constructing the tree:

<xsl:try>
  <xsl:result-document href="out.xml" validation="strict">  
    <xsl:call-template name="construct-output"/>
  </xsl:result-document>
  <xsl:catch>
    <xsl:message>Warning: validation of result document failed:
          Error code: <xsl:value-of select="$err:code"/>
          Reason: <xsl:value-of select="$err:description"/>
    </xsl:message>
    <xsl:call-template name="construct-output"/>
  </xsl:catch>
  </xsl:try>

9 Variables and Parameters

[Definition: The two elements xsl:variable and xsl:param are referred to as variable-binding elements ].

[Definition: The xsl:variable element declares a variable, which may be a global variable or a local variable.]

[Definition: The xsl:param element declares a parameter, which may be a stylesheet parameter, a template parameter, a function parameter, or an xsl:iterate parameter. A parameter is a variable with the additional property that its value can be set by the caller.]

[Definition: A variable is a binding between a name and a value. The value of a variable is any sequence (of nodes, atomic values, and/or function items), as defined in [Data Model].]

9.1 Variables

<!-- Category: declaration -->
<!-- Category: instruction -->
<xsl:variable
  name = eqname
  select? = expression
  as? = sequence-type
  static? = "yes" | "no"
  visibility? = "public" | "private" | "final" | "abstract" >
  <!-- Content: sequence-constructor -->
</xsl:variable>

The xsl:variable element has a required name attribute, which specifies the name of the variable. The value of the name attribute is an EQName, which is expanded as described in 5.1 Qualified Names.

The xsl:variable element has an optional as attribute, which specifies the required type of the variable. The value of the as attribute is a SequenceTypeXP30, as defined in [XPath 3.0].

[Definition: The value of the variable is computed using the expression given in the select attribute or the contained sequence constructor, as described in 9.3 Values of Variables and Parameters. This value is referred to as the supplied value of the variable.] If the xsl:variable element has a select attribute, then the sequence constructor must be empty.

If the as attribute is specified, then the supplied value of the variable is converted to the required type, using the function conversion rules.

[ERR XTTE0570] It is a type error if the supplied value of a variable cannot be converted to the required type.

If the as attribute is omitted, the supplied value of the variable is used directly, and no conversion takes place.

For the effect of the static attribute, see 9.6 Static Variables and Parameters.

The visibility attribute must not be specified for a local variable: that is, it is allowed only when the parent element is xsl:stylesheet, xsl:transform, or xsl:override.

If the visibility attribute is present with the value abstract then the select attribute must be absent and the contained sequence constructor must be empty. In this situation there is no supplied value, and therefore the constraint that the supplied value is consistent with the required type does not apply.

9.2 Parameters

<!-- Category: declaration -->
<xsl:param
  name = eqname
  select? = expression
  as? = sequence-type
  required? = "yes" | "no"
  tunnel? = "yes" | "no"
  static? = "yes" | "no"
  visibility? = "public" | "private" | "final" | "abstract" >
  <!-- Content: sequence-constructor -->
</xsl:param>

The xsl:param element may be used:

The xsl:param element has a required name attribute, which specifies the name of the parameter. The value of the name attribute is an EQName, which is expanded as described in 5.1 Qualified Names.

[ERR XTSE0580] It is a static error if the values of the name attribute of two sibling xsl:param elements represent the same expanded QName.

Note:

For rules concerning stylesheet parameters, see 9.5 Global Variables and Parameters. Local variables may shadow template parameters and function parameters: see 9.9 Scope of Variables.

The supplied value of the parameter is the value supplied by the caller. If no value was supplied by the caller, and if the parameter is not mandatory, then the supplied value is computed using the expression given in the select attribute or the contained sequence constructor, as described in 9.3 Values of Variables and Parameters. If the xsl:param element has a select attribute, then the sequence constructor must be empty.

Note:

This specification does not dictate whether and when the default value of a parameter is evaluated. For example, if the default is specified as <xsl:param name="p"><foo/></xsl:param>, then it is not specified whether a distinct foo element node will be created on each invocation of the template, or whether the same foo element node will be used for each invocation. However, it is permissible for the default value to depend on the values of other parameters, or on the evaluation context, in which case the default must effectively be evaluated on each invocation.

The xsl:param element has an optional as attribute, which specifies the required type of the parameter. The value of the as attribute is a SequenceTypeXP30, as defined in [XPath 3.0].

If the as attribute is specified, then the supplied value of the parameter is converted to the required type, using the function conversion rules.

[ERR XTTE0590] It is a type error if the conversion of the supplied value of a parameter to its required type fails.

If the as attribute is omitted, the supplied value of the parameter is used directly, and no conversion takes place.

The optional required attribute may be used to indicate that a parameter is mandatory. This attribute may be specified for stylesheet parameters and for template parameters; it must not be specified for function parameters, which are always mandatory, or for parameters to xsl:iterate, which are always initialized to a default value. A parameter is mandatory if it is a function parameter or if the required attribute is present and has the value yes. Otherwise, the parameter is optional. If the parameter is mandatory, then the xsl:param element must be empty and must not have a select attribute.

[ERR XTTE0600] If a default value is given explicitly, that is, if there is either a select attribute or a non-empty sequence constructor, then it is a type error if the default value cannot be converted to the required type, using the function conversion rules.

If a stylesheet parameter specifies required="yes" and does not specify static="yes", then its visibility must be public, final, or abstract. The default visibility of such a parameter is public.

[ERR XTSE3370] It is a static error if the the visibility attribute of a stylesheet parameter that specifies required="yes" and does not specify static="yes" is present with a value other than public, final, or abstract, or if an xsl:expose or xsl:accept declaration attempts to modify the visibility of such a component to a value other than public, final, or abstract.

Note:

This rule has the effect that after combining all the packages making up a stylesheet, the non-static stylesheet parameters whose values are required necessarily have distinct names, which simplifies the design of APIs.

If an optional parameter has no select attribute and has an empty sequence constructor, and if there is no as attribute, then the default value of the parameter is a zero length string.

[ERR XTDE0610] If an optional parameter has no select attribute and has an empty sequence constructor, and if there is an as attribute, then the default value of the parameter is an empty sequence. If the empty sequence is not a valid instance of the required type defined in the as attribute, then the parameter is treated as a required parameter, which means that it is a dynamic error if the caller supplies no value for the parameter.

For the effect of the static attribute, see 9.6 Static Variables and Parameters.

The visibility attribute must not be specified for a local parameter: that is, it is allowed only when the parent element is xsl:stylesheet, xsl:transform, or xsl:override.

If the visibility attribute is present with the value abstract then the select attribute must be absent and the contained sequence constructor must be empty. In this situation there is no supplied value, and therefore the constraint that the supplied value is consistent with the required type does not apply.

Note:

The effect of these rules is that specifying <xsl:param name="p" as="xs:date" select="2"/> is an error, but if the default value of the parameter is never used, then the processor has discretion whether or not to report the error. By contrast, <xsl:param name="p" as="xs:date"/> is treated as if required="yes" had been specified: the empty sequence is not a valid instance of xs:date, so in effect there is no default value and the parameter is therefore treated as being mandatory.

The optional tunnel attribute may be used to indicate that a parameter is a tunnel parameter. The default is no; the value yes may be specified only for template parameters. Tunnel parameters are described in 10.1.2 Tunnel Parameters

9.3 Values of Variables and Parameters

A variable-binding element may specify the supplied value of a variable or the default value of a parameter in four different ways.

  • If the variable-binding element has a select attribute, then the value of the attribute must be an expression and the supplied value of the variable is the value that results from evaluating the expression. In this case, the content of the variable-binding element must be empty.

  • If the variable-binding element has empty content and has neither a select attribute nor an as attribute, then the supplied value of the variable is a zero-length string. Thus

    <xsl:variable name="x"/>
    

    is equivalent to

    <xsl:variable name="x" select="''"/>
    
  • If a variable-binding element has no select attribute and has non-empty content (that is, the variable-binding element has one or more child nodes), and has no as attribute, then the content of the variable-binding element specifies the supplied value. The content of the variable-binding element is a sequence constructor; a new document is constructed with a document node having as its children the sequence of nodes that results from evaluating the sequence constructor and then applying the rules given in 5.8.1 Constructing Complex Content. The value of the variable is then a singleton sequence containing this document node. For further information, see 9.4 Creating Implicit Document Nodes.

  • If a variable-binding element has an as attribute but no select attribute, then the supplied value is the sequence that results from evaluating the (possibly empty) sequence constructor contained within the variable-binding element (see 5.8 Sequence Constructors).

These combinations are summarized in the table below.

select attribute as attribute content Effect
present absent empty Value is obtained by evaluating the select attribute
present present empty Value is obtained by evaluating the select attribute, adjusted to the type required by the as attribute
present absent present Static error
present present present Static error
absent absent empty Value is a zero-length string
absent present empty Value is an empty sequence, provided the as attribute permits an empty sequence
absent absent present Value is a document node whose content is obtained by evaluating the sequence constructor
absent present present Value is obtained by evaluating the sequence constructor, adjusted to the type required by the as attribute

[ERR XTSE0620] It is a static error if a variable-binding element has a select attribute and has non-empty content.

Example: Values of Variables

The value of the following variable is the sequence of integers (1, 2, 3):

<xsl:variable name="i" as="xs:integer*" select="1 to 3"/>

The value of the following variable is an integer, assuming that the attribute @size exists, and is annotated either as an integer, or as xs:untypedAtomic:

<xsl:variable name="i" as="xs:integer" select="@size"/>

The value of the following variable is a zero-length string:

<xsl:variable name="z"/>

The value of the following variable is a document node containing an empty element as a child:

<xsl:variable name="doc"><c/></xsl:variable>

The value of the following variable is a sequence of integers (2, 4, 6):

<xsl:variable name="seq" as="xs:integer*">
  <xsl:for-each select="1 to 3">
    <xsl:sequence select=".*2"/>
  </xsl:for-each>
</xsl:variable>

The value of the following variable is a sequence of parentless attribute nodes:

<xsl:variable name="attset" as="attribute()+">
  <xsl:attribute name="x">2</xsl:attribute>
  <xsl:attribute name="y">3</xsl:attribute>
  <xsl:attribute name="z">4</xsl:attribute>    
</xsl:variable>

The value of the following variable is an empty sequence:

<xsl:variable name="empty" as="empty-sequence()"/>

The actual value of the variable depends on the supplied value, as described above, and the required type, which is determined by the value of the as attribute.

Example: Pitfalls with Numeric Predicates

When a variable is used to select nodes by position, be careful not to do:

<xsl:variable name="n">2</xsl:variable>
...
<xsl:value-of select="td[$n]"/>

This will output the values of all the td elements, space-separated (or with XSLT 1.0 behavior, the value of the first td element), because the variable n will be bound to a node, not a number. Instead, do one of the following:

<xsl:variable name="n" select="2"/>
...
<xsl:value-of select="td[$n]"/>

or

<xsl:variable name="n">2</xsl:variable>
...
<xsl:value-of select="td[position()=$n]"/>

or

<xsl:variable name="n" as="xs:integer">2</xsl:variable>
...
<xsl:value-of select="td[$n]"/>

9.4 Creating Implicit Document Nodes

A document node is created implicitly when evaluating an xsl:variable, xsl:param, or xsl:with-param element that has non-empty content and that has no as attribute. The value of the variable is a single node, the document node of a temporary tree. The content of the document node is formed from the result of evaluating the sequence constructor contained within the variable-binding element, as described in 5.8.1 Constructing Complex Content.

Note:

The construct:

<xsl:variable name="tree">
  <a/>
</xsl:variable>

can be regarded as a shorthand for:

<xsl:variable name="tree" as="document-node()">
  <xsl:document validation="preserve">
    <a/>
  </xsl:document>  
</xsl:variable>

The base URI of the document node is taken from the base URI of the variable binding element in the stylesheet. (See Section 5.2 base-uri Accessor DM30 in [Data Model])

No document-level validation takes place (which means, for example, that there is no checking that ID values are unique). However, type annotations on nodes within the new tree are copied unchanged.

Note:

The base URI of other nodes in the tree is determined by the rules for constructing complex content. The effect of these rules is that the base URI of a node in the temporary tree is determined as if all the nodes in the temporary tree came from a single entity whose URI was the base URI of the variable-binding element. Thus, the base URI of the document node will be equal to the base URI of the variable-binding element, while an xml:base attribute within the temporary tree will change the base URI for its parent element and that element's descendants, just as it would within a document constructed by parsing.

The document-uri and unparsed-entities properties of the new document node are set to empty.

A temporary tree is available for processing in exactly the same way as any source document. For example, its nodes are accessible using path expressions, and they can be processed using instructions such as xsl:apply-templates and xsl:for-each. Also, the key and idFO30 functions can be used to find nodes within a temporary tree, by supplying the document node at the root of the tree as an argument to the function or by making it the context node.

Example: Two-Phase Transformation

For example, the following stylesheet uses a temporary tree as the intermediate result of a two-phase transformation, using different modes for the two phases (see 6.6 Modes). Typically, the template rules in module phase1.xsl will be declared with mode="phase1", while those in module phase2.xsl will be declared with mode="phase2":

<xsl:stylesheet
  version="3.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:import href="phase1.xsl"/>
<xsl:import href="phase2.xsl"/>

<xsl:variable name="intermediate">
  <xsl:apply-templates select="/" mode="phase1"/>
</xsl:variable>

<xsl:template match="/">
  <xsl:apply-templates select="$intermediate" mode="phase2"/>
</xsl:template>

</xsl:stylesheet>

Note:

The algorithm for matching nodes against template rules is exactly the same regardless which tree the nodes come from. If different template rules are to be used when processing different trees, then unless nodes from different trees can be distinguished by means of patterns, it is a good idea to use modes to ensure that each tree is processed using the appropriate set of template rules.

9.5 Global Variables and Parameters

Both xsl:variable and xsl:param are allowed as declaration elements: that is, they may appear as children of the xsl:stylesheet element.

[Definition: A top-level variable-binding element declares a global variable that is visible everywhere (except within its own declaration, and where it is shadowed by another binding).]

[Definition: A top-level xsl:param element declares a stylesheet parameter. A stylesheet parameter is a global variable with the additional property that its value can be supplied by the caller when a transformation is initiated.] As described in 9.2 Parameters, a stylesheet parameter may be declared as being mandatory, or may have a default value specified for use when no value is supplied by the caller. The mechanism by which the caller supplies a value for a stylesheet parameter is implementation-defined. An XSLT processor must provide such a mechanism.

It is an error if no value is supplied for a mandatory stylesheet parameter [see ERR XTDE0050].

If a stylesheet contains more than one binding for a global variable of a particular name, then the binding with the highest import precedence is used.

[ERR XTSE0630] It is a static error if a stylesheet contains more than one non-hidden binding of a global variable with the same name and same import precedence, unless it also contains another binding with the same name and higher import precedence.

For a global variable or the default value of a stylesheet parameter, the expression or sequence constructor specifying the variable value is evaluated with a singleton focus based on the root node of the tree containing the initial context item. An XPath error will be reported if the evaluation of a global variable or parameter references the context item, context position, or context size when no initial context item is supplied. The values of other components of the dynamic context are the initial values as defined in 5.4.3 Initializing the Dynamic Context and 5.4.4 Additional Dynamic Context Components used by XSLT.

Example: A Stylesheet Parameter

The following example declares a global parameter para-font-size, which is referenced in an attribute value template.

<xsl:param name="para-font-size" as="xs:string">12pt</xsl:param>

<xsl:template match="para">
 <fo:block font-size="{$para-font-size}">
   <xsl:apply-templates/>
 </fo:block>
</xsl:template>

The implementation must provide a mechanism allowing the user to supply a value for the parameter para-font-size when invoking the stylesheet; the value 12pt acts as a default.

9.6 Static Variables and Parameters

Static variables and parameters are global variables and can be used in the same way as other global variables. In addition, they can be used in [xsl:]use-when expressions.

[Definition: A top-level variable-binding element having the attribute static="yes" declares a static variable: that is, a global variable whose value is known during static analysis of the stylesheet.]

[Definition: A static variable declared using an xsl:param element is referred to as a static parameter.]

The static attribute must not be present on an xsl:variable or xsl:param element unless it is a top-level element.

When the static attribute is present with the value yes, the visibility attribute must not have a value other than private or final.

Note:

This rule prevents static variables being overridden in another package. Since the values of such variables may be used at compile time (for example, during processing of [xsl:]use-when expressions), the rule is necessary to ensure that packages can be independently compiled.

Declaring a static variable or parameter with visibility="final" allows its value to be used in ordinary (non-static) expressions in a using package, but use in static expressions is possible only within the same package.

When the attribute static="yes" is specified, the xsl:variable or xsl:param element must have empty content. In the case of xsl:variable the select attribute must be present to define the value of the variable.

If the select attribute is present, then it is evaluated using the rules for static expressions.

9.7 Static Expressions

[Definition: A static expression is an XPath expression whose value must be computed during static analysis of the stylesheet.]

Static expressions appear in two contexts:

There are no syntactic constraints on the XPath expression that can be used as a static expression. However, there are severe constraints on the information provided in its evaluation context. These constraints are designed to ensure that the expression can be evaluated at the earliest possible stage of stylesheet processing, without any dependency on information contained in the stylesheet itself or in any source document.

Specifically, the components of the static and dynamic context are defined by the following two tables:

Static Context Components for Static Expressions
Component Value
XPath 1.0 compatibility mode false
Statically known namespaces determined by the in-scope namespaces for the containing element in the stylesheet
Default element/type namespace determined by the xpath-default-namespace attribute if present (see 5.2 Unprefixed Lexical QNames in Expressions and Patterns); otherwise the null namespace
Default function namespace The standard function namespace
In-scope schema types The type definitions that would be available in the absence of any xsl:import-schema declaration
In-scope element declarations None
In-scope attribute declarations None
In-scope variables The static variables visible within the containing package whose declarations occur prior to the element containing the static expression in stylesheet tree order. Stylesheet tree order is the order that results when all xsl:import and xsl:include declarations are replaced by the declarations in the imported or included stylesheet module. A static variable is not in scope within its own declaration, and it is in scope only within its declaring package, not in any using packages. If two static variables satisfying this rule have the same name and are both in scope, the one that has highest import precedence is used (it is a consequence of rules defined elsewhere that there cannot be more than one declaration with highest import precedence). Note that the declaration with highest import precedence is not necessarily the one that appears last in stylesheet tree order; note also that because forwards references are not allowed, the declaration that is used will not necessarily be the one with highest import precedence in the stylesheet as a whole.
Context item static type Absent
Statically known function signatures The core functions defined in [Functions and Operators], together with the functions element-available, function-available, type-available, and system-property defined in this specification, plus the set of extension functions that are present in the static context of every XPath expression (other than a use-when expression) within the content of the element that is the parent of the use-when attribute. Note that stylesheet functions are not included in the context, which means that the function function-available will return false in respect of such functions. The effect of this rule is to ensure that function-available returns true in respect of functions that can be called within the scope of the use-when attribute. It also has the effect that these extension functions will be recognized within the use-when attribute itself; however, the fact that a function is available in this sense gives no guarantee that a call on the function will succeed.
Statically known collations Implementation-defined
Default collation The Unicode Codepoint Collation
Static Base URI The base URI of the containing element in the stylesheet document (see Section 5.2 base-uri Accessor DM30)
Statically known documents Implementation-defined
Statically known collections Implementation-defined
Statically known default collection type Implementation-defined
Statically known decimal formats A single unnamed decimal format equivalent to the decimal format that is created by an xsl:decimal-format declaration with no attributes.

 

Dynamic Context Components for Static Expressions
Component Value
Context item, position, and size Absent
Variable values A value for every variable present in the in-scope variables. For static parameters where an external value is supplied: the externally-supplied value of the parameter. In all other cases: the value of the variable as defined in 9.3 Values of Variables and Parameters.
Named functions The function implementation corresponding to each function signature in the statically known function signatures
Current dateTime Implementation-defined
Implicit timezone Implementation-defined
Default language Implementation-defined
Default calendar Implementation-defined
Default place Implementation-defined
Available documents Implementation-defined
Available collections Implementation-defined
Default collection Implementation-defined
Environment variables Implementation-defined

Within a stylesheet module, all static expressions are evaluated in a single execution scopeFO30. This need not be the same execution scope as that used for static expressions in other stylesheet modules, or as that used when evaluating XPath expressions appearing elsewhere in the stylesheet module. This means that a function such as current-dateFO30 will return the same result when called in different [xsl:]use-when expressions within the same stylesheet module, but will not necessarily return the same result as the same call in an [xsl:]use-when expression within a different stylesheet module, or as a call on the same function executed during the transformation proper.

9.8 Local Variables and Parameters

[Definition: As well as being allowed as a declaration, the xsl:variable element is also allowed in sequence constructors. Such a variable is known as a local variable.]

An xsl:param element may also be used to create a variable binding with local scope:

The result of evaluating a local xsl:variable or xsl:param element (that is, the contribution it makes to the result of the sequence constructor it is part of) is an empty sequence.

9.9 Scope of Variables

For any variable-binding element, there is a region (more specifically, a set of nodes) of the stylesheet within which the binding is visible. The set of variable bindings in scope for an XPath expression consists of those bindings that are visible at the point in the stylesheet where the expression occurs.

A global variable binding element is visible everywhere in the stylesheet (including other stylesheet modules) except within the xsl:variable or xsl:param element itself and any region where it is shadowed by another variable binding.

A local variable binding element is visible for all following siblings and their descendants, with the following exceptions:

  1. It is not visible in any region where it is shadowed by another variable binding.

  2. It is not visible within the subtree rooted at an xsl:fallback instruction that is a sibling of the variable binding element.

  3. It is not visible within the subtree rooted at an xsl:catch instruction that is a sibling of the variable binding element.

The binding is not visible for the xsl:variable or xsl:param element itself.

If a binding is visible for an element then it is visible for every attribute of that element and for every text node child of that element.

[Definition: A binding shadows another binding if the binding occurs at a point where the other binding is visible, and the bindings have the same name. ] It is not an error if a binding established by a local xsl:variable or xsl:param shadows a global binding. In this case, the global binding will not be visible in the region of the stylesheet where it is shadowed by the other binding.

Example: Local Variable Shadowing a Global Variable

The following is allowed:

<xsl:param name="x" select="1"/>
<xsl:template name="foo">
  <xsl:variable name="x" select="2"/>
</xsl:template>

It is also not an error if a binding established by a local xsl:variable element shadows a binding established by another local xsl:variable or xsl:param.

Example: Misuse of Variable Shadowing

The following is not an error, but the effect is probably not what was intended. The template outputs <x value="1"/>, because the declaration of the inner variable named $x has no effect on the value of the outer variable named $x.

<xsl:variable name="x" select="1"/>
<xsl:template name="foo">
  <xsl:for-each select="1 to 5">
    <xsl:variable name="x" select="$x+1"/>
  </xsl:for-each>
  <x value="{$x}"/>
</xsl:template>

Note:

Once a variable has been given a value, the value cannot subsequently be changed. XSLT does not provide an equivalent to the assignment operator available in many procedural programming languages.

This is because an assignment operator would make it harder to create an implementation that processes a document other than in a batch-like way, starting at the beginning and continuing through to the end.

As well as global variables and local variables, an XPath expression may also declare range variables for use locally within an expression. For details, see [XPath 3.0].

Where a reference to a variable occurs in an XPath expression, it is resolved first by reference to range variables that are in scope, then by reference to local variables and parameters, and finally by reference to global variables and parameters. A range variable may shadow a local variable or a global variable. XPath also allows a range variable to shadow another range variable.

9.10 Setting Parameter Values

<xsl:with-param
  name = eqname
  select? = expression
  as? = sequence-type
  tunnel? = "yes" | "no" >
  <!-- Content: sequence-constructor -->
</xsl:with-param>

Parameters are passed to templates using the xsl:with-param element. The required name attribute specifies the name of the template parameter (the variable the value of whose binding is to be replaced). The value of the name attribute is an EQName, which is expanded as described in 5.1 Qualified Names.

The xsl:with-param element is also used when passing parameters to an iteration of the xsl:iterate instruction, or to a dynamic invocation of an XPath expression using xsl:evaluate. In consequence, xsl:with-param may appear within xsl:apply-templates, xsl:apply-imports, xsl:call-template, xsl:evaluate, xsl:next-iteration, and xsl:next-match. (Arguments to stylesheet functions, however, are supplied as part of an XPath function call: see 10.3 Stylesheet Functions.)

[ERR XTSE0670] It is a static error if two or more sibling xsl:with-param elements have name attributes that represent the same expanded QName.

The value of the parameter is specified in the same way as for xsl:variable and xsl:param (see 9.3 Values of Variables and Parameters), taking account of the values of the select and as attributes and the content of the xsl:with-param element, if any.

Note:

It is possible to have an as attribute on the xsl:with-param element that differs from the as attribute on the corresponding xsl:param element.

In this situation, the supplied value of the parameter will first be processed according to the rules of the as attribute on the xsl:with-param element, and the resulting value will then be further processed according to the rules of the as attribute on the xsl:param element.

For example, suppose the supplied value is a node with type annotation xs:untypedAtomic, and the xsl:with-param element specifies as="xs:integer", while the xsl:param element specifies as="xs:double". Then the node will first be atomized and the resulting untyped atomic value will be cast to xs:integer. If this succeeds, the xs:integer will then be promoted to an xs:double.

The focus used for computing the value specified by the xsl:with-param element is the same as that used for its parent instruction.

The optional tunnel attribute may be used to indicate that a parameter is a tunnel parameter. The default is no. Tunnel parameters are described in 10.1.2 Tunnel Parameters. They are used only when passing parameters to templates: for an xsl:with-param element that is a child of xsl:evaluate or xsl:next-iteration the tunnel attribute must either be omitted or take the value no.

In other cases it is a dynamic error if the template that is invoked declares a template parameter with required="yes" and no value for this parameter is supplied by the calling instruction. [see ERR XTDE0700]

9.11 Circular Definitions

[Definition: A circularity is said to exist if a construct such as a global variable, an attribute set, or a key, is defined in terms of itself. For example, if the expression or sequence constructor specifying the value of a global variable X references a global variable Y, then the value for Y must be computed before the value of X. A circularity exists if it is impossible to do this for all global variable definitions.]

Example: Circular Variable Definitions

The following two declarations create a circularity:

<xsl:variable name="x" select="$y+1"/>
<xsl:variable name="y" select="$x+1"/>

 

Example: Circularity involving Variables and Functions

The definition of a global variable can be circular even if no other variable is involved. For example the following two declarations (see 10.3 Stylesheet Functions for an explanation of the xsl:function element) also create a circularity:

<xsl:variable name="x" select="my:f()"/>

<xsl:function name="my:f">
  <xsl:sequence select="$x"/>
</xsl:function>

 

Example: Circularity involving Variables and Templates

The definition of a variable is also circular if the evaluation of the variable invokes an xsl:apply-templates instruction and the variable is referenced in the pattern used in the match attribute of any template rule in the stylesheet. For example the following definition is circular:

<xsl:variable name="x">
  <xsl:apply-templates select="//param[1]"/>
</xsl:variable>

<xsl:template match="param[$x]">1</xsl:template>

 

Example: Circularity involving Variables and Keys

Similarly, a variable definition is circular if it causes a call on the key function, and the definition of that key refers to that variable in its match or use attributes. So the following definition is circular:

<xsl:variable name="x" select="my:f(10)"/>

<xsl:function name="my:f">
  <xsl:param name="arg1"/>
  <xsl:sequence select="key('k', $arg1)"/>
</xsl:function>

<xsl:key name="k" match="item[@code=$x]" use="@desc"/>

[ERR XTDE0640] In general, a circularity in a stylesheet is a dynamic error. However, as with all other dynamic errors, an implementation will signal the error only if it actually executes the instructions and expressions that participate in the circularity. Because different implementations may optimize the execution of a stylesheet in different ways, it is implementation-dependent whether a particular circularity will actually be signaled.

For example, in the following declarations, the function declares a local variable $b, but it returns a result that does not require the variable to be evaluated. It is implementation-dependent whether the value is actually evaluated, and it is therefore implementation-dependent whether the circularity is signaled as an error:

<xsl:variable name="x" select="my:f(1)"/>

<xsl:function name="my:f">
  <xsl:param name="a"/>
  <xsl:variable name="b" select="$x"/>  
  <xsl:sequence select="$a + 2"/>
</xsl:function>

Circularities usually involve global variables or parameters, but they can also exist between key definitions (see 20.2 Keys), between named attribute sets (see 10.2 Named Attribute Sets), or between any combination of these constructs. For example, a circularity exists if a key definition invokes a function that references an attribute set that calls the key function, supplying the name of the original key definition as an argument.

Circularity is not the same as recursion. Stylesheet functions (see 10.3 Stylesheet Functions) and named templates (see 10.1 Named Templates) may call other functions and named templates without restriction. With careless coding, recursion may be non-terminating. Implementations are required to signal circularity as a dynamic error, but they are not required to detect non-terminating recursion.

10 Callable Components

This section describes three constructs that can be used to provide subroutine-like functionality that can be invoked from anywhere in the stylesheet: named templates (see 10.1 Named Templates), named attribute sets (see 10.2 Named Attribute Sets), and stylesheet functions (see 10.3 Stylesheet Functions).

10.1 Named Templates

<!-- Category: instruction -->
<xsl:call-template
  name = eqname >
  <!-- Content: xsl:with-param* -->
</xsl:call-template>

[Definition: Templates can be invoked by name. An xsl:template element with a name attribute defines a named template.] The value of the name attribute is an EQName, which is expanded as described in 5.1 Qualified Names. If an xsl:template element has a name attribute, it may, but need not, also have a match attribute. An xsl:call-template instruction invokes a template by name; it has a required name attribute that identifies the template to be invoked. Unlike xsl:apply-templates, the xsl:call-template instruction does not change the focus.

The match, mode and priority attributes on an xsl:template element have no effect when the template is invoked by an xsl:call-template instruction. Similarly, the name and visibility attributes on an xsl:template element have no effect when the template is invoked by an xsl:apply-templates instruction.

[ERR XTSE0650] It is a static error if a stylesheet contains an xsl:call-template instruction whose name attribute does not match the name attribute of any named template visible in the containing package (this includes any template defined in this package, as well as templates accepted from used packages whose visibility in this package is not hidden). For more details of the process of binding the called template, see 3.6.2.6 Binding References to Components.

[ERR XTSE0660] It is a static error if a package contains more than one non-hidden template with the same name and the same import precedence, unless it also contains a template with the same name and higher import precedence.

[ERR XTSE3340] It is a static error if an xsl:template declaration has the name xsl:initial-template and contains an xsl:param that specifies required="yes".

The target template for an xsl:call-template instruction is established using the binding rules described in 3.6.2.6 Binding References to Components. This will always be a template whose name attribute matches the name attribute of the xsl:call-template instruction. It may be a template defined in the same package that has higher import precedence than any other template with this name, or it may be a template accepted from a used package, or (if the template is not defined as private or final) it may be an overriding template in a package that uses the containing package. The result of evaluating an xsl:call-template instruction is the sequence produced by evaluating the sequence constructor contained in its target template (see 5.8 Sequence Constructors).

The template name xsl:initial-template is specially recognized in that it provides a default entry point for stylesheet execution (see 2.3 Initiating a Transformation.) A template with this name must not have any xsl:param children that specify required="yes". In all other respects a template with this name behaves exactly like a template with any other name.

10.1.1 Passing Parameters to Named Templates

Parameters are passed to named templates using the xsl:with-param element as a child of the xsl:call-template instruction.

[ERR XTSE0680] In the case of xsl:call-template, it is a static error to pass a non-tunnel parameter named x to a template that does not have a non-tunnel template parameter named x, unless the xsl:call-template instruction is processed with XSLT 1.0 behavior. This is not an error in the case of xsl:apply-templates, xsl:apply-imports, and xsl:next-match; in these cases the parameter is simply ignored.

The optional tunnel attribute may be used to indicate that a parameter is a tunnel parameter. The default is no. Tunnel parameters are described in 10.1.2 Tunnel Parameters

[ERR XTSE0690] It is a static error if a template that is invoked using xsl:call-template declares a template parameter specifying required="yes" and not specifying tunnel="yes", if no value for this parameter is supplied by the calling xsl:call-template instruction.

Example: Calling a Named Template with a Parameter

This example defines a named template for a numbered-block with a parameter to control the format of the number.

<xsl:template name="numbered-block">
  <xsl:param name="format">1. </xsl:param>
  <fo:block>
    <xsl:number format="{$format}"/>
    <xsl:apply-templates/>
  </fo:block>
</xsl:template>

<xsl:template match="ol//ol/li">
  <xsl:call-template name="numbered-block">
    <xsl:with-param name="format">a. </xsl:with-param>
  </xsl:call-template>
</xsl:template>

10.1.2 Tunnel Parameters

[Definition: A parameter passed to a template may be defined as a tunnel parameter. Tunnel parameters have the property that they are automatically passed on by the called template to any further templates that it calls, and so on recursively.] Tunnel parameters thus allow values to be set that are accessible during an entire phase of stylesheet processing, without the need for each template that is used during that phase to be aware of the parameter.

Note:

Tunnel parameters are conceptually similar to dynamically scoped variables in some functional programming languages.

A tunnel parameter is created by using an xsl:with-param element that specifies tunnel="yes". A template that requires access to the value of a tunnel parameter must declare it using an xsl:param element that also specifies tunnel="yes".

On any template call using an xsl:apply-templates, xsl:call-template, xsl:apply-imports or xsl:next-match instruction, a set of tunnel parameters is passed from the calling template to the called template. This set consists of any parameters explicitly created using <xsl:with-param tunnel="yes">, overlaid on a base set of tunnel parameters. If the xsl:apply-templates, xsl:call-template, xsl:apply-imports or xsl:next-match instruction has an xsl:template declaration as an ancestor element in the stylesheet, then the base set consists of the tunnel parameters that were passed to that template; otherwise (for example, if the instruction is within a global variable declaration, an attribute set declaration, or a stylesheet function), the base set is empty. If a parameter created using <xsl:with-param tunnel="yes"> has the same expanded QName as a parameter in the base set, then the parameter created using xsl:with-param overrides the parameter in the base set; otherwise, the parameter created using xsl:with-param is added to the base set.

When a template accesses the value of a tunnel parameter by declaring it with xsl:param tunnel="yes", this does not remove the parameter from the base set of tunnel parameters that is passed on to any templates called by this template.

Two sibling xsl:with-param elements must have distinct parameter names, even if one is a tunnel parameter and the other is not. Equally, two sibling xsl:param elements representing template parameters must have distinct parameter names, even if one is a tunnel parameter and the other is not. However, the tunnel parameters that are implicitly passed in a template call may have names that duplicate the names of non-tunnel parameters that are explicitly passed on the same call.

Tunnel parameters are not passed in calls to stylesheet functions.

All other options of xsl:with-param and xsl:param are available with tunnel parameters just as with non-tunnel parameters. For example, parameters may be declared as mandatory or optional, a default value may be specified, and a required type may be specified. If any conversion is required from the supplied value of a tunnel parameter to the required type specified in xsl:param, then the converted value is used within the receiving template, but the value that is passed on in any further template calls is the original supplied value before conversion. Equally, any default value is local to the template: specifying a default value for a tunnel parameter does not change the set of tunnel parameters that is passed on in further template calls.

The set of tunnel parameters that is passed to the initial template is empty.

Tunnel parameters are passed unchanged through a built-in template rule (see 6.8 Built-in Template Rules).

If a tunnel parameter is declared in an xsl:param element with the attribute tunnel="yes", then a dynamic error occurs [see ERR XTDE0700] if the set of tunnel parameters passed to the template does not include a parameter with a matching expanded QName.

Example: Using Tunnel Parameters

Suppose that the equations in a scientific paper are to be sequentially numbered, but that the format of the number depends on the context in which the equations appear. It is possible to reflect this using a rule of the form:

<xsl:template match="equation">
  <xsl:param name="equation-format" select="'(1)'" tunnel="yes"/>
  <xsl:number level="any" format="{$equation-format}"/>
</xsl:template>

At any level of processing above this level, it is possible to determine how the equations will be numbered, for example:

<xsl:template match="appendix">
  ...
  <xsl:apply-templates>
    <xsl:with-param name="equation-format" select="'[i]'" tunnel="yes"/>
  </xsl:apply-templates>
  ...
</xsl:template>

The parameter value is passed transparently through all the intermediate layers of template rules until it reaches the rule with match="equation". The effect is similar to using a global variable, except that the parameter can take different values during different phases of the transformation.

10.2 Named Attribute Sets

<!-- Category: declaration -->
<xsl:attribute-set
  name = eqname
  use-attribute-sets? = eqnames
  visibility? = "public" | "private" | "final" | "abstract"
  streamable? = "yes" | "no" >
  <!-- Content: xsl:attribute* -->
</xsl:attribute-set>

Attribute sets generate named collections of attributes that can be used repeatedly on different constructed elements. The xsl:attribute-set declaration is used to declare attribute sets. The required name attribute specifies the name of the attribute set. The value of the name attribute is an EQName, which is expanded as described in 5.1 Qualified Names.

[Definition: An attribute set is defined as a set of xsl:attribute-set declarations in the same package that share the same expanded QName.]

The content of the xsl:attribute-set element consists of zero or more xsl:attribute instructions that are evaluated to produce the attributes in the set.

10.2.1 Using Attribute Sets

Attribute sets are used by specifying a use-attribute-sets attribute on the xsl:element or xsl:copy instruction, or by specifying an xsl:use-attribute-sets attribute on a literal result element. An attribute set may be defined in terms of other attribute sets by using the use-attribute-sets attribute on the xsl:attribute-set element itself. The value of the [xsl:]use-attribute-sets attribute is in each case a whitespace-separated list of names of attribute sets. Each name is specified as an EQName, which is expanded as described in 5.1 Qualified Names.

Specifying a use-attribute-sets attribute is broadly equivalent to adding xsl:attribute instructions for each of the attributes in each of the named attribute sets to the beginning of the content of the instruction with the [xsl:]use-attribute-sets attribute, in the same order in which the names of the attribute sets are specified in the use-attribute-sets attribute.

More formally, an xsl:use-attribute-sets attribute is expanded using the following recursive algorithm, or any algorithm that produces the same results:

  • The value of the attribute is tokenized as a list of QNames.

  • Each QName in the list is processed, in order, as follows:

    • The QName must match the name attribute of one or more xsl:attribute-set declarations in the stylesheet.

    • Each xsl:attribute-set declaration whose name matches is processed as follows. Where two such declarations have different import precedence, the one with lower import precedence is processed first. Where two declarations have the same import precedence, they are processed in declaration order.

[ERR XTSE0710] It is a static error if the value of the use-attribute-sets attribute of an xsl:copy, xsl:element, or xsl:attribute-set element, or the xsl:use-attribute-sets attribute of a literal result element, is not a whitespace-separated sequence of EQNames, or if it contains a QName that does not match the name attribute of any xsl:attribute-set declaration in the stylesheet.

[ERR XTSE0720] It is a static error if an xsl:attribute-set element directly or indirectly references itself via the names contained in the use-attribute-sets attribute.

10.2.2 Visibility of Attribute Sets

The visibility attribute determines the potential visibility of the attribute set in packages other than the containing package. If the visibility attribute is present on any of the xsl:attribute-set declarations making up the definition of an attribute set (that is, all declarations within the same package sharing the same name), then it must be present, with the same value, on every xsl:attribute-set declaration making up the definition of that attribute set.

If the visibility attribute is present with the value abstract then there must be no xsl:attribute children and no use-attribute-sets attribute.

10.2.3 Streamability of Attribute Sets

An attribute set may be designated as streamable by including the attribute streamable="yes" on each xsl:attribute-set declaration making up the attribute set. If any xsl:attribute-set declaration for an attribute set has the attribute streamable="yes", then every xsl:attribute-set declaration for that attribute set must have the attribute streamable="yes".

An attribute set is guaranteed-streamable if every xsl:attribute-set declaration making up the attribute set, considered as a sequence constructor, is motionless according to the analysis in 19.8.5 Classifying Attribute Sets.

Specifying streamable="yes" on an xsl:attribute-set element declares an intent that the attribute set should be guaranteed streamable according to these criteria. The consequences of declaring the attribute set to be streamable when it is not in fact guaranteed streamable depend on the conformance level of the processor, and are explained in 19.10 Streamability Guarantees.

Note:

It is common for attribute sets to create attributes with constant values, and such attribute sets will always be motionless and therefore streamable. Although such cases are fairly simple for a processor to detect, references to attribute sets are not guaranteed streamable unless the attribute set is declared with the attribute streamable="yes", which should therefore be used if interoperable streaming is required.

10.2.4 Evaluating Attribute Sets

Attribute sets are evaluated as follows:

  • The xsl:copy and xsl:element instructions have an use-attribute-sets attribute. The sequence of attribute nodes produced by evaluating this attribute is prepended to the sequence produced by evaluating the sequence constructor contained within the instruction.

  • Literal result elements allow an xsl:use-attribute-sets attribute, which is evaluated in the same way as the use-attribute-sets attribute of xsl:element and xsl:copy. The sequence of attribute nodes produced by evaluating this attribute is prepended to the sequence of attribute nodes produced by evaluating the attributes of the literal result element, which in turn is prepended to the sequence produced by evaluating the sequence constructor contained with the literal result element.

The xsl:attribute instructions are evaluated using the same focus as is used for evaluating the element that is the parent of the [xsl:]use-attribute-sets attribute forming the initial input to the algorithm. However, the static context for the evaluation depends on the position of the xsl:attribute instruction in the stylesheet: thus, only local variables declared within an xsl:attribute instruction, and global variables, are visible.

The set of attribute nodes produced by expanding xsl:use-attribute-sets may include several attributes with the same name. When the attributes are added to an element node, only the last of the duplicates will take effect.

The way in which each instruction uses the results of expanding the [xsl:]use-attribute-sets attribute is described in the specification for the relevant instruction: see 11.1 Literal Result Elements, 11.2 Creating Element Nodes Using xsl:element , and 11.9 Copying Nodes.

The result of evaluating an attribute set is a sequence of attribute nodes. Evaluating the same attribute set more than once can produce different results, because although an attribute set does not have parameters, it may contain expressions or instructions whose value depends on the evaluation context.

Each attribute node produced by expanding an attribute set has a type annotation determined by the rules for the xsl:attribute instruction that created the attribute node: see 11.3.1 Setting the Type Annotation for a Constructed Attribute Node. These type annotations may be preserved, stripped, or replaced as determined by the rules for the instruction that creates the element in which the attributes are used.

10.2.5 Attribute Sets: Examples

Example: A Simple Attribute Set

The following example creates a named attribute set title-style and uses it in a template rule.

<xsl:template match="chapter/heading">
  <fo:block font-stretch="condensed" xsl:use-attribute-sets="title-style">
    <xsl:apply-templates/>
  </fo:block>
</xsl:template>

<xsl:attribute-set name="title-style">
  <xsl:attribute name="font-size">12pt</xsl:attribute>
  <xsl:attribute name="font-weight">bold</xsl:attribute>
</xsl:attribute-set>

 

Example: Overriding Attributes in an Attribute Set

The following example creates a named attribute set base-style and uses it in a template rule with multiple specifications of the attributes:

font-family

is specified only in the attribute set

font-size

is specified in the attribute set, is specified on the literal result element, and in an xsl:attribute instruction

font-style

is specified in the attribute set, and on the literal result element

font-weight

is specified in the attribute set, and in an xsl:attribute instruction

Stylesheet fragment:

<xsl:attribute-set name="base-style">
  <xsl:attribute name="font-family">Univers</xsl:attribute>
  <xsl:attribute name="font-size">10pt</xsl:attribute>
  <xsl:attribute name="font-style">normal</xsl:attribute>
  <xsl:attribute name="font-weight">normal</xsl:attribute>
</xsl:attribute-set>

<xsl:template match="o">
  <fo:block xsl:use-attribute-sets="base-style"
            font-size="12pt"
            font-style="italic">
    <xsl:attribute name="font-size">14pt</xsl:attribute>
    <xsl:attribute name="font-weight">bold</xsl:attribute>
    <xsl:apply-templates/>
  </fo:block>
</xsl:template>

Result:

<fo:block font-family="Univers"
          font-size="14pt"
          font-style="italic"
          font-weight="bold">
...
</fo:block>

10.3 Stylesheet Functions

[Definition: An xsl:function declaration declares the name, parameters, and implementation of a stylesheet function that can be called from any XPath expression within the stylesheet.]

<!-- Category: declaration -->
<xsl:function
  name = eqname
  as? = sequence-type
  visibility? = "public" | "private" | "final" | "abstract"
  override-extension-function? = "yes" | "no"
  [override]? = "yes" | "no"
  identity-sensitive? = "yes" | "no"
  cache? = "full" | "partial" | "no" >
  <!-- Content: (xsl:param*, sequence-constructor) -->
</xsl:function>

The xsl:function declaration defines a stylesheet function that can be called from any XPath expression used in the stylesheet (including an XPath expression used within a predicate in a pattern). The name attribute specifies the name of the function. The value of the name attribute is an EQName, which is expanded as described in 5.1 Qualified Names.

An xsl:function declaration can only appear as a top-level element in a stylesheet module.

The content of the xsl:function element consists of zero or more xsl:param elements that specify the formal arguments of the function, followed by a sequence constructor that defines the value to be returned by the function.

10.3.1 Function Name and Arity

The name of the function is given by the name attribute; the arguments are defined by child xsl:param elements; and the return type is defined by the as attribute. Together these definitions constitute the function signature.

[ERR XTSE0740] It is a static error if a stylesheet function has a name that is in no namespace.

Note:

To prevent the namespace declaration used for the function name appearing in the result document, use the exclude-result-prefixes attribute on the xsl:stylesheet element: see 11.1.3 Namespace Nodes for Literal Result Elements.

The name of the function must not be in a reserved namespace: [see ERR XTSE0080]

[Definition: The arity of a stylesheet function is the number of xsl:param elements in the function definition.] Optional arguments are not allowed.

As defined in XPath, the function that is executed as the result of a function call is identified by looking in the in-scope functions of the static context for a function whose name and arity matches the name and number of arguments in the function call.

Note:

Functions are not polymorphic. Although the XPath function call mechanism allows two functions to have the same name and different arity, it does not allow them to be distinguished by the types of their arguments.

10.3.2 Arguments

The xsl:param elements define the formal arguments to the function. These are interpreted positionally. When the function is called using a function-call in an XPath expression, the first argument supplied is assigned to the first xsl:param element, the second argument supplied is assigned to the second xsl:param element, and so on.

[ERR XTSE0760] Because arguments to a stylesheet function call must all be specified, the xsl:param elements within an xsl:function element must not specify a default value: this means they must be empty, and must not have a select attribute.

The as attribute of the xsl:param element defines the required type of the parameter. The rules for converting the values of the actual arguments supplied in the function call to the types required by each xsl:param element are defined in [XPath 3.0]. The rules that apply are those for the case where XPath 1.0 compatibility mode is set to false.

[ERR XTTE0790] If the value of a parameter to a stylesheet function cannot be converted to the required type, a type error is signaled.

If the as attribute is omitted, no conversion takes place and any value is accepted.

10.3.3 Function Result

The result of the function is the result of evaluating the contained sequence constructor.

Within the sequence constructor, the focus is initially absent; this means that any attempt to reference the context item, context position, or context size is a dynamic error. [ERR XPDY0002] XP30

It is not possible within the body of the stylesheet function to access the values of local variables that were in scope in the place where the function call was written. Global variables, however, remain available.

The optional as attribute indicates the required type of the result of the function. The value of the as attribute is a SequenceTypeXP30, as defined in [XPath 3.0].

[ERR XTTE0780] If the as attribute is specified, then the result evaluated by the sequence constructor (see 5.8 Sequence Constructors) is converted to the required type, using the function conversion rules. It is a type error if this conversion fails. If the as attribute is omitted, the calculated result is used as supplied, and no conversion takes place.

10.3.4 Visibility and Overriding of Functions

If the visibility attribute is present with the value abstract then the sequence constructor defining the function body must be empty.

A stylesheet function is included in the in-scope functions of the static context for all XPath expressions used in the containing package, unless

  • there is another stylesheet function with the same name and arity, and higher import precedence, or

  • the override-extension-function or override attribute has the value no and there is already a function with the same name and arity in the in-scope functions.

The visibility of the function in other packages depends on the value of the visibility attribute and other factors, as described in 3.6 Packages

The optional override-extension-function attribute defines what happens if this function has the same name and arity as a function provided by the implementer or made available in the static context using an implementation-defined mechanism. If the override-extension-function attribute has the value yes, then this function is used in preference; if it has the value no, then the other function is used in preference. The default value is yes.

Note:

Specifying override-extension-function="yes" ensures interoperable behavior: the same code will execute with all processors. Specifying override-extension-function="no" is useful when writing a fallback implementation of a function that is available with some processors but not others: it allows the vendor's implementation of the function (or a user's implementation written as an extension function) to be used in preference to the stylesheet implementation, which is useful when the extension function is more efficient.

The override-extension-function attribute does not affect the rules for deciding which of several stylesheet functions with the same name and arity takes precedence.

The override attribute is a deprecated synonym of override-extension-function, retained for compatibility with XSLT 2.0. If both attributes are present then they must have the same value.

[ERR XTSE0770] It is a static error for a package to contain two or more non-hidden functions with the same expanded QName, the same arity, and the same import precedence, unless there is another function with the same expanded QName and arity, and a higher import precedence.

When the xsl:function declaration appears as a child of xsl:override, there must be a stylesheet function with the same expanded QName and arity in the package referenced by the containing xsl:use-package element; the visibility of that function must be public or abstract, and the overriding and overridden functions must have the same argument types and result type.

10.3.5 Dynamic Access to Functions

If a stylesheet function with a particular expanded QName and arity exists in the stylesheet, then a call to the function-lookupFO30 function supplying that name and arity will return the function as a value. This applies only if the static context for the call on function-lookupFO30 includes the stylesheet function, which implies that the function is visible in the containing package.

The function-available function, when called with a particular expanded QName and arity, returns true if and only if a call on function-lookupFO30 with the same arguments, in the same static context, would return a function item.

Note:

For legacy reasons there is also a single-argument version of function-available, which returns true if there is a function with the given name regardless of arity.

The standard rules for function-lookupFO30 require that if the supplied name and arity identify a context-dependent function such as name#0FO30 or lang#1FO30 (call it F), then the returned function value includes in its closure a copy of the static and dynamic context of the call to function-lookupFO30, and the context item for a subsequent dynamic call of F is taken from this saved context. In the case where the context item is a node in a streamed input document, saving the node is not possible. In this case, therefore, the context is saved with an absent focus, so the call on F will fail with a dynamic error saying that there is no context item available.

10.3.6 Determinism of Functions

Stylesheet functions have been designed to be largely deterministic: unless a stylesheet function calls some extension function which is itself non-deterministic, the function will return results that depend only on the supplied arguments. This property (coupled with the fact that the effect of calling extension functions is entirely implementation-dependent) enables a processor to implement various optimizations, such as removing invariant function calls from the body of a loop, or combining common sub-expressions,.

One exception to the intrinsic determinism of stylesheet functions arises because constructed nodes have distinct identity. This means that when a function that creates a new node is called, two calls on the function will return nodes that can be distinguished: for example, with such a function, f:make-node() is f:make-node() will return false. This property of functions is called identity-sensitivity. If a processor cannot determine by static analysis that the function is not identity-sensitive, then it cannot perform optimizations that would observably change this behavior.

To allow processors greater freedom to optimize calls on stylesheet functions, the attribute identity-sensitive="no" may be specified (the default is yes). When the value no is specified, the stylesheet author is asserting that for any node passed in the value of an argument to the function, and for any node returned as a result, the stylesheet as a whole will give acceptable results if the node is replaced by a different node that is deep-equal to the original.

Note:

Note the term "acceptable". The result of the transformation may be different, but not in a way that the stylesheet author cares about.

Declaring a function with identity-sensitive="no" might allow a call to the function to be moved out of a loop, so the function is only called once before entry to the loop rather than being called repeatedly within the loop. If the arguments to the function depend only on global variables then it might enable the function call to be moved into a global variable. It might also enable some caching or memoization at the processor's discretion.

Declaring a function with identity-sensitive="no" might also allow nodes from a streamed input document to be passed to the function, since the function is licensed to operate on a deep copy of the node. However, the streamability analysis in this specification does not take account of this possibility.

10.3.7 Memoization

The cache attribute is an optimization hint which the processor can use or ignore at its discretion; however it should be taken seriously, because it may make a difference to whether execution of a stylesheet is practically feasible or not.

The default value is cache="no".

The value cache="full" encourages the processor to retain memory of all previous calls of this function during the same transformation and to reuse results from this memory whenever possible. The value cache="partial" encourages the processor to retain such memory but to discard results if necessary to keep the amount of memory used within bounds. The default value cache="no" encourages the processor not to retain memory of previous calls.

In all cases the results must respect the semantics; for example if an attribute node is supplied as the value of an argument, then its identity must be assumed to be significant unless (a) identity-sensitive="no" is specified, or (b) the processor is able to determine by static analysis that the identity of the attribute node makes no difference to the result (for example, because all references to the argument are atomizing references).

Note:

Memoization using the cache attribute may be more effective if the attribute identity-sensitive="no" is also used, as this gives a processor more scope for optimization. In particular, specifying cache="full" by itself does not remove the obligation of a processor to return distinct nodes on each call of a function, whereas combining this with identity-sensitive="no" does remove this obligation.

10.3.8 Examples of Stylesheet Functions

Example: A Stylesheet Function

The following example creates a recursive stylesheet function named str:reverse that reverses the words in a supplied sentence, and then invokes this function from within a template rule.

<xsl:transform 
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:xs="http://www.w3.org/2001/XMLSchema"
  xmlns:str="http://example.com/namespace"
  version="3.0"
  exclude-result-prefixes="str">

<xsl:function name="str:reverse" as="xs:string">
  <xsl:param name="sentence" as="xs:string"/>
  <xsl:sequence  
     select="if (contains($sentence, ' '))
             then concat(str:reverse(substring-after($sentence, ' ')),
                         ' ',
                         substring-before($sentence, ' '))
             else $sentence"/>
</xsl:function>

<xsl:template match="/">
<output>
  <xsl:value-of select="str:reverse('DOG BITES MAN')"/>
</output>
</xsl:template>

</xsl:transform>

An alternative way of writing the same function is to implement the conditional logic at the XSLT level, thus:

<xsl:function name="str:reverse" as="xs:string">
  <xsl:param name="sentence" as="xs:string"/>
  <xsl:choose>
    <xsl:when test="contains($sentence, ' ')">  
      <xsl:sequence 
           select="concat(str:reverse(substring-after($sentence, ' ')),
                                ' ',
                                substring-before($sentence, ' '))"/>
    </xsl:when>
    <xsl:otherwise>
      <xsl:sequence select="$sentence"/>
    </xsl:otherwise>
  </xsl:choose>
</xsl:function>

 

Example: Declaring the Return Type of a Function

The following example illustrates the use of the as attribute in a function definition. It returns a string containing the representation of its integer argument, expressed as a roman numeral. For example, the function call num:roman(7) will return the string "vii". This example uses the xsl:number instruction, described in 12 Numbering. The xsl:number instruction returns a text node, and the function conversion rules are invoked to convert this text node to the type declared in the xsl:function element, namely xs:string. So the text node is atomized to a string.

<xsl:function name="num:roman" as="xs:string">
  <xsl:param name="value" as="xs:integer"/>
  <xsl:number value="$value" format="i"/>
</xsl:function>

 

Example: A Higher-Order Function

XPath 3.0 introduces the ability to pass function items as argument to a function. A function that takes function items as arguments is known as a higher-order function.

The following example is a higher-order function that operates on any tree-structured data, for example an organization chart. Given as input a function that finds the direct subordinates of a node in this tree structure (for example, the direct reports of a manager, or the geographical subdivisions of an administrative area), it determines whether one object is present in the subtree rooted at another object (for example, whether one person is among the staff managed directly or indirectly by a manager, or whether one parcel of land is contained directly or indirectly within another parcel. The function does not check for cycles in the data.

<xsl:function name="f:is-subordinate" as="xs:boolean">
    <xsl:param name="superior" 
               as="node()"/>
    <xsl:param name="subordinate" 
               as="node()"/>
    <xsl:param name="get-direct-children" 
               as="function(node()) as node()*"/>
    <xsl:sequence select="
               some $sub in $get-direct-children($superior) satisfies
                 ($sub is $subordinate or
                  f:is-subordinate($sub, $subordinate, 
                                      $get-direct-children))"/>
</xsl:function>

Given source data representing an organization chart in the form of elements such as:

<employee id="P57832" manager="P68951"/>

the following function can be defined to get the direct reports of a manager:

<xsl:function name="f:direct-reports" 
               as="element(employee)*">
    <xsl:param name="manager" as="element(employee)"/>
    <xsl:sequence select="$manager/../employee
                               [@manager = $manager/@id]"/>
</xsl:function>

It is then possible to test whether one employee $E reports directly or indirectly to another employee $M by means of the function call:

f:is-subordinate($M, $E, f:direct-reports#1)

10.4 Dynamic XPath Evaluation

<!-- Category: instruction -->
<xsl:evaluate
  xpath = expression
  as? = sequence-type
  base-uri? = { uri }
  with-params? = expression
  context-item? = expression
  namespace-context? = expression
  schema-aware? = { "yes" | "no" } >
  <!-- Content: (xsl:with-param | xsl:fallback)* -->
</xsl:evaluate>

The xsl:evaluate instruction constructs an XPath expression in the form of a string, evaluates the expression in a specified context, and returns the result of the evaluation.

The expression given as the value of the xpath attribute is evaluated and the result is converted to a string using the function conversion rules.

[Definition: The string that results from evaluating the expression in the xpath attribute is referred to as the target expression.]

[ERR XTDE3160] It is a dynamic error if the target expression is not a valid XPath 3.0 expression (that is, if a static error occurs when analyzing the string according to the rules of the XPath 3.0 specification).

The as attribute, if present, indicates the required type of the result. If the attribute is absent, the required type is item()*, which allows any result. The result of evaluating the target expression is converted to the required type using the function conversion rules. This may cause a type error if conversion is not possible. The result after conversion is returned as the result of the xsl:evaluate instruction.

The target expression may contain variable references; the values of such variables may be supplied using an xsl:with-param child instruction if the names of the variables are known statically, or using a map supplied as the value of the expression in the with-params attribute if the names are only known dynamically. If the with-params attribute is present then it must contain an expression whose value, when evaluated, is of type map(xs:QName, item()*) (see 21.1 Maps for details of maps).

10.4.1 Static context for the target expression

The static contextXP30 for the target expression is as follows:

  • XPath 1.0 compatibility mode is false.

  • Statically known namespaces and default element/type namespace:

    • if the namespace-context attribute is present, then its value is an expression whose required type is a single node. The expression is evaluated, and the in-scope namespaces of the resulting node are used as the statically known namespaces for the target expression. The binding for the default namespace in the in-scope namespaces is used as the default namespace for elements and types in the target expression.

      [ERR XTTE3170] It is a type error if the result of evaluating the namespace-context attribute of the xsl:evaluate instruction is anything other than a single node.

    • if the namespace-context attribute is absent, then the in-scope namespaces of the xsl:evaluate instruction (with the exception of any binding for the default namespace) are used as the statically known namespaces for the target expression, and the value of the innermost [xsl:]xpath-default-namespace attribute, if any, is used as the default namespace for elements and types in the target expression.

    Note:

    XPath 3.0 allows expanded names to be written in a context-independent way using the syntax Q{namespace-uri}local-name

  • Default function namespace: the standard function namespace.

  • In-scope schema definitions: if the schema-aware attribute is present and has the effective value yes, then the in-scope schema definitions from the stylesheet context (that is, the schema definitions imported using xsl:import-schema). Otherwise, the built-in types (see 3.15 Built-in Types).

  • In-scope variables: the names of the in-scope variables are the union of the names appearing in the name attribute of the contained xsl:with-param elements, and the names present as keys in the map obtained by evaluating the with-params attribute, if present. The corresponding type is item()* in the case of a name found as a key in the with-params map, or the type named in the as attribute of xsl:with-param child (defaulting to item()*) otherwise.

    Note:

    Variables declared in the stylesheet in xsl:variable or xsl:param elements are not in-scope within the target expression.

    If variable names are present in both the static xsl:with-param children and also in the dynamic with-params map, the value from the latter takes precedence.

  • Function signatures: All core functions; constructor functions for named simple types included in the in-scope schema definitions; all user-defined functions and accumulator functions present in the containing package provided their visibility is not hidden or private; and an implementation-defined set of extension functions.

    Note that this set deliberately excludes XSLT-defined functions in the standard function namespace including for example, key, current-group, and system-property A list of these functions is in G List of XSLT-defined functions.

  • Statically known collations: the same as the collations available at this point in the stylesheet.

  • Default collation: the same as the default collation defined at this point in the stylesheet (for example, by use of the [xsl:]default-collation attribute)

  • Base URI: if the base-uri attribute is present, then its effective value; otherwise, the base URI of the xsl:evaluate instruction.

  • Statically known documents: the empty set

  • Statically known collections: the empty set

  • Statically known default collection type: node()*

10.4.2 Dynamic context for the target expression

The dynamic context for evaluation of the target expression is as follows:

  • The context item, position, and size depend on the result of evaluating the expression in the context-item attribute. If this attribute is absent, or if the result is an empty sequence, then the context item, position, and size for evaluation of the target expression are all absent. If the result of evaluating the context-item expression is a single item, then the target expression is evaluated with a singleton focus based on this item.

    [ERR XTTE3210] If the result of evaluating the context-item expression is a sequence containing more than one item, then a type error is signaled.

  • The variable values consists of the values bound to parameters defined either in the contained xsl:with-param elements, which are evaluated as described in 9.3 Values of Variables and Parameters, or in the map that results from evaluation of the expression in the with-params attribute; if the same QName is bound in both, the value in the with-params map takes precedence.

  • The XSLT-specific aspects of the dynamic context described in 5.4.4 Additional Dynamic Context Components used by XSLT are all absent.

  • All other aspects of the dynamic context are the same as the dynamic context for the xsl:evaluate instruction itself.

10.4.3 The effect of the xsl:evaluate instruction

The XPath expression is evaluated in the same execution scopeFO30 as the calling XSLT transformation; this means that the results of deterministicFO30 functions such as docFO30 or current-dateTimeFO30 will be consistent between the calling stylesheet and the called XPath expression.

It is a dynamic error if evaluation of the XPath expression fails with a dynamic error. The XPath-defined error code is used unchanged.

Note:

Implementations wanting to avoid the cost of repeated compilation of the same XPath expression should cache the compiled form internally.

Stylesheet authors need to be aware of the security risks associated with the use of xsl:evaluate. The instruction should not be used to execute code from an untrusted source. To avoid the risk of code injection, user-supplied data should never be inserted into the expression using string concatenation, but should always be referenced by use of parameters.

10.4.4 xsl:evaluate as an optional feature

The xsl:evaluate instruction is newly introduced in XSLT 3.0. It is part of the dynamic evaluation feature, which is an optional feature of the specification (see 26.6 Dynamic Evaluation Feature). An XSLT 3.0 processor may disable the feature, or allow users to disable the feature. The processor may be able to determine during static analysis whether or not the feature is available, or it may only be able to determine this during dynamic evaluation. In the first case we refer to the feature being statically disabled, in the second case to it being dynamically disabled.

If the feature is statically disabled, then:

  • A call to element-available('xsl:evaluate') returns false, wherever it appears;

  • A call to system-property('xsl:supports-dynamic-evaluation') returns "no", wherever it appears;

  • If an xsl:evaluate instruction has an xsl:fallback child, fallback processing takes place;

  • No static error is raised if an xsl:evaluate instruction is present in the stylesheet (an error occurs only if it is actually evaluated).

If the feature is dynamically disabled, then:

  • A call to element-available('xsl:evaluate') appearing in a static expression (for example, in an [xsl:]use-when attribute) returns true;

  • A call to element-available('xsl:evaluate') appearing anywhere else returns false;

  • A call to system-property('xsl:supports-dynamic-evaluation') appearing in a static expression (for example, in an [xsl:]use-when attribute) returns "yes";

  • A call to system-property('xsl:supports-dynamic-evaluation') appearing anywhere else returns "no";

  • If an xsl:evaluate instruction has an xsl:fallback child, fallback processing takes place;

  • In the absence of an xsl:fallback child, a dynamic error is raised if an xsl:evaluate instruction is evaluated. The dynamic error may be caught using xsl:try and xsl:catch.

[ERR XTDE3175] It is a dynamic error if an xsl:evaluate instruction is evaluated when use of xsl:evaluate has been statically or dynamically disabled.

In consequence of these rules, the recommended approach for stylesheet authors to write code that works whether or not xsl:evaluate is enabled is to use an xsl:fallback child instruction. For example:

    <xsl:variable name="isValid" as="xs:boolean">
      <xsl:evaluate xpath="$validityCondition">
         <xsl:fallback><xsl:sequence select="true()"/></xsl:fallback>
      </xsl:evaluate>
      </xsl:variable>

Note:

There may be circumstances where it is inappropriate to allow use of xsl:evaluate. For example:

  • There may be security risks associated with the ability to execute code from an untrusted source, which cannot be inspected during static analysis.

  • There may be environments where the the available computing resources are sufficient to enable pre-compiled stylesheets to be executed, but not to enable XPath expressions to be compiled into executable code.

Processors that implement xsl:evaluate should provide mechanisms allowing calls on xsl:evaluate to be disabled. Implementations may disable the feature by default, and they may disable it unconditionally.

10.4.5 Examples of xsl:evaluate

Example: Using a Dynamic Sort Key

A common requirement is to sort a table on the value of an expression which is selected at run-time, perhaps by supplying the expression as a string-valued parameter to the stylesheet. Suppose that such an expression is supplied to the parameter:

<xsl:param name="sortkey" as="xs:string" select="'@name'"/>

Then the data may be sorted as follows:

<xsl:sort>
   <xsl:evaluate xpath="$sortkey" as="xs:string" context-item="."/>
</xsl:sort>

Note the importance in this use case of caching the compiled expression, since it is evaluated repeatedly, once for each item in the list being sorted.

 

Example: Getting a Function if it Exists

The function-lookupFO30 function, if it were not available in the standard library, could be implemented like this:

     <xsl:function name="f:function-lookup">
       <xsl:param name="name" as="xs:QName"/>
       <xsl:param name="arity" as="xs:integer"/>
       <xsl:evaluate xpath="'Q{' || namespace-uri-from-QName($name) || '}' 
                      || local-name-from-QName($name) || '#' || $arity">
         <xsl:with-param name="name" as="xs:QName" select="$name"/>
         <xsl:with-param name="arity" as="xs:integer" select="$arity"/>
       </xsl:evaluate>
     </xsl:function>  
     

The xsl:evaluate instruction uses the supplied QName and arity to construct an expression of the form Q{namespace-uri}local#arity, which is then evaluated to return a function item representing the requested function.

11 Creating Nodes and Sequences

This section describes instructions that directly create new nodes, or sequences of nodes, atomic values, and/or function items.

11.1 Literal Result Elements

[Definition: In a sequence constructor, an element in the stylesheet that does not belong to the XSLT namespace and that is not an extension instruction (see 23.2 Extension Instructions) is classified as a literal result element.] A literal result element is evaluated to construct a new element node with the same expanded QName (that is, the same namespace URI, local name, and namespace prefix). The result of evaluating a literal result element is a node sequence containing one element, the newly constructed element node.

The content of the element is a sequence constructor (see 5.8 Sequence Constructors). The sequence obtained by evaluating this sequence constructor, after prepending any attribute nodes produced as described in 11.1.2 Attribute Nodes for Literal Result Elements and namespace nodes produced as described in 11.1.3 Namespace Nodes for Literal Result Elements, is used to construct the content of the element, following the rules in 5.8.1 Constructing Complex Content

The base URI of the new element is copied from the base URI of the literal result element in the stylesheet, unless the content of the new element includes an xml:base attribute, in which case the base URI of the new element is the value of that attribute, resolved (if it is a relative URI reference) against the base URI of the literal result element in the stylesheet. (Note, however, that this is only relevant when creating a parentless element. When the literal result element is copied to form a child of an element or document node, the base URI of the new copy is taken from that of its new parent.)

11.1.1 Setting the Type Annotation for Literal Result Elements

The attributes xsl:type and xsl:validation may be used on a literal result element to invoke validation of the contents of the element against a type definition or element declaration in a schema, and to determine the type annotation that the new element node will carry. These attributes also affect the type annotation carried by any elements and attributes that have the new element node as an ancestor. These two attributes are both optional, and if one is specified then the other must be omitted.

The value of the xsl:validation attribute, if present, must be one of the values strict, lax, preserve, or strip. The value of the xsl:type attribute, if present, must be an EQName identifying a type definition that is present in the in-scope schema components for the stylesheet. Neither attribute may be specified as an attribute value template. The effect of these attributes is described in 24.2 Validation.

11.1.2 Attribute Nodes for Literal Result Elements

Attribute nodes for a literal result element may be created by including xsl:attribute instructions within the sequence constructor. Additionally, attribute nodes are created corresponding to the attributes of the literal result element in the stylesheet, and as a result of expanding the xsl:use-attribute-sets attribute of the literal result element, if present.

The sequence that is used to construct the content of the literal result element (as described in 5.8.1 Constructing Complex Content) is the concatenation of the following four sequences, in order:

  1. The sequence of namespace nodes produced as described in 11.1.3 Namespace Nodes for Literal Result Elements.

  2. The sequence of attribute nodes produced by expanding the xsl:use-attribute-sets attribute (if present) following the rules given in 10.2 Named Attribute Sets

  3. The attributes produced by processing the attributes of the literal result element itself, other than attributes in the XSLT namespace. The way these are processed is described below.

  4. The sequence produced by evaluating the contained sequence constructor, if the element is not empty.

Note:

The significance of this order is that an attribute produced by an xsl:attribute, xsl:copy, or xsl:copy-of instruction in the content of the literal result element takes precedence over an attribute produced by expanding an attribute of the literal result element itself, which in turn takes precedence over an attribute produced by expanding the xsl:use-attribute-sets attribute. This is because of the rules in 5.8.1 Constructing Complex Content, which specify that when two or more attributes in the sequence have the same name, all but the last of the duplicates are discarded.

Although the above rules place namespace nodes before attributes, this is not strictly necessary, because the rules in 5.8.1 Constructing Complex Content allow the namespaces and attributes to appear in any order so long as both come before other kinds of node. The order of namespace nodes and attribute nodes in the sequence has no effect on the relative position of the nodes in document order once they are added to a tree.

Each attribute of the literal result element, other than an attribute in the XSLT namespace, is processed to produce an attribute for the element in the result tree.

The value of such an attribute is interpreted as an attribute value template: it can therefore contain expressions contained in curly brackets ({}). The new attribute node will have the same expanded QName (that is, the same namespace URI, local name, and namespace prefix) as the attribute in the stylesheet tree, and its string value will be the same as the effective value of the attribute in the stylesheet tree. The type annotation on the attribute will initially be xs:untypedAtomic, and the typed value of the attribute node will be the same as its string value.

Note:

The eventual type annotation of the attribute in the result tree depends on the xsl:validation and xsl:type attributes of the parent literal result element, and on the instructions used to create its ancestor elements. If the xsl:validation attribute is set to preserve or strip, the type annotation will be xs:untypedAtomic, and the typed value of the attribute node will be the same as its string value. If the xsl:validation attribute is set to strict or lax, or if the xsl:type attribute is used, the type annotation on the attribute will be set as a result of the schema validation process applied to the parent element. If neither attribute is present, the type annotation on the attribute will be xs:untypedAtomic.

If the name of a constructed attribute is xml:id, the processor must perform attribute value normalization by effectively applying the normalize-spaceFO30 function to the value of the attribute, and the resulting attribute node must be given the is-id property.

Note:

If the attribute name is xml:space, it is not an error when the value is something other than default or preserve. Although the XML specification states that other values are erroneous, a document containing such values is well-formed; if erroneous values are to be rejected, schema validation should be used.

Note:

The xml:base, xml:lang, xml:space, and xml:id attributes have two effects in XSLT. They behave as standard XSLT attributes, which means for example that if they appear on a literal result element, they will be copied to the result tree in the same way as any other attribute. In addition, they have their standard meaning as defined in the core XML specifications. Thus, an xml:base attribute in the stylesheet affects the base URI of the element on which it appears, and an xml:space attribute affects the interpretation of whitespace text nodes within that element. One consequence of this is that it is inadvisable to write these attributes as attribute value templates: although an XSLT processor will understand this notation, the XML parser will not. See also 11.1.5 Namespace Aliasing which describes how to use xsl:namespace-alias with these attributes.

The same is true of the schema-defined attributes xsi:type, xsi:nil, xsi:noNamespaceSchemaLocation, and xsi:schemaLocation. If the stylesheet is processed by a schema processor, these attributes will be recognized and interpreted by the schema processor, but in addition the XSLT processor treats them like any other attribute on a literal result element: that is, their effective value (after expanding attribute value templates) is copied to the result tree in the same way as any other attribute. If the result tree is validated, the copied attributes will again be recognized and interpreted by the schema processor.

None of these attributes will be generated in the result tree unless the stylesheet writes them to the result tree explicitly, in the same way as any other attribute.

[ERR XTSE0805] It is a static error if an attribute on a literal result element is in the XSLT namespace, unless it is one of the attributes explicitly defined in this specification.

Note:

If there is a need to create attributes in the XSLT namespace, this can be achieved using xsl:attribute, or by means of the xsl:namespace-alias declaration.

11.1.3 Namespace Nodes for Literal Result Elements

The created element node will have a copy of the namespace nodes that were present on the element node in the stylesheet tree with the exception of any namespace node whose string value is designated as an excluded namespace. Special considerations apply to aliased namespaces: see 11.1.5 Namespace Aliasing

The following namespaces are designated as excluded namespaces:

  • The XSLT namespace URI (http://www.w3.org/1999/XSL/Transform)

  • A namespace URI declared as an extension namespace (see 23.2 Extension Instructions)

  • A namespace URI designated by using an [xsl:]exclude-result-prefixes attribute either on the literal result element itself or on an ancestor element. The attribute must be in the XSLT namespace only if its parent element is not in the XSLT namespace.

    The value of the attribute is either #all, or a whitespace-separated list of tokens, each of which is either a namespace prefix or #default. The namespace bound to each of the prefixes is designated as an excluded namespace.

    [ERR XTSE0808] It is a static error if a namespace prefix is used within the [xsl:]exclude-result-prefixes attribute and there is no namespace binding in scope for that prefix.

    The default namespace of the parent element of the [xsl:]exclude-result-prefixes attribute (see Section 6.2 Element Nodes DM30) may be designated as an excluded namespace by including #default in the list of namespace prefixes.

    [ERR XTSE0809] It is a static error if the value #default is used within the [xsl:]exclude-result-prefixes attribute and the parent element of the [xsl:]exclude-result-prefixes attribute has no default namespace.

    The value #all indicates that all namespaces that are in scope for the stylesheet element that is the parent of the [xsl:]exclude-result-prefixes attribute are designated as excluded namespaces.

    The designation of a namespace as an excluded namespace is effective within the subtree of the stylesheet module rooted at the element bearing the [xsl:]exclude-result-prefixes attribute; a subtree rooted at an xsl:stylesheet element does not include any stylesheet modules imported or included by children of that xsl:stylesheet element.

The excluded namespaces, as described above, only affect namespace nodes copied from the stylesheet when processing a literal result element. There is no guarantee that an excluded namespace will not appear on the result tree for some other reason. Namespace nodes are also written to the result tree as part of the process of namespace fixup (see 5.8.3 Namespace Fixup), or as the result of instructions such as xsl:copy and xsl:element.

Note:

When a stylesheet uses a namespace declaration only for the purposes of addressing a source tree, specifying the prefix in the [xsl:]exclude-result-prefixes attribute will avoid superfluous namespace declarations in the serialized result tree. The attribute is also useful to prevent namespaces used solely for the naming of stylesheet functions or extension functions from appearing in the serialized result tree.

Example: Excluding Namespaces from the Result Tree

For example, consider the following stylesheet:

<xsl:stylesheet version="1.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:a="a.uri"
  xmlns:b="b.uri"
  exclude-result-prefixes="#all">
  
<xsl:template match="/">
  <foo xmlns:c="c.uri" xmlns:d="d.uri" xmlns:a2="a.uri" 
       xsl:exclude-result-prefixes="c"/>
</xsl:template>

</xsl:stylesheet>

The result of this stylesheet will be:

<foo xmlns:d="d.uri"/>

The namespaces a.uri and b.uri are excluded by virtue of the exclude-result-prefixes attribute on the xsl:stylesheet element, and the namespace c.uri is excluded by virtue of the xsl:exclude-result-prefixes attribute on the foo element. The setting #all does not affect the namespace d.uri because d.uri is not an in-scope namespace for the xsl:stylesheet element. The element in the result tree does not have a namespace node corresponding to xmlns:a2="a.uri" because the effect of exclude-result-prefixes is to designate the namespace URI a.uri as an excluded namespace, irrespective of how many prefixes are bound to this namespace URI.

If the stylesheet is changed so that the literal result element has an attribute b:bar="3", then the element in the result tree will typically have a namespace declaration xmlns:b="b.uri" (the processor may choose a different namespace prefix if this is necessary to avoid conflicts). The exclude-result-prefixes attribute makes b.uri an excluded namespace, so the namespace node is not automatically copied from the stylesheet, but the presence of an attribute whose name is in the namespace b.uri forces the namespace fixup process (see 5.8.3 Namespace Fixup) to introduce a namespace node for this namespace.

A literal result element may have an optional xsl:inherit-namespaces attribute, with the value yes or no. The default value is yes. If the value is set to yes, or is omitted, then the namespace nodes created for the newly constructed element are copied to the children and descendants of the newly constructed element, as described in 5.8.1 Constructing Complex Content. If the value is set to no, then these namespace nodes are not automatically copied to the children. This may result in namespace undeclarations (such as xmlns="" or, in the case of XML 1.1, xmlns:p="") appearing on the child elements when a final result tree is serialized.

11.1.4 Conditional Creation of Literal Result Elements

If a literal result element has an xsl:on-empty attribute, then the value of the attribute must be an XPath expression. If the attribute is present and the constructed element has no attributes and no children, then instead of returning the constructed element, the instruction returns the result of evaluating the expression in the xsl:on-empty attribute; if this expression returns a node, the instruction returns a copy of this node.

[ERR XTTE3300] It is a type error if the result of evaluating the xsl:on-empty attribute does not satisfy the required type element()?. That is, the expression must deliver either a single element node, or an empty sequence.

If the xsl:on-empty expression is evaluated and returns an empty sequence, then the xsl:validation and xsl:type attributes are ignored. However, if the result of the xsl:on-empty expression is an element, then it is subjected to validation as determined by these attributes, along with [xsl:]default-validation where relevant.

Note that when a literal result element has one or more attributes (other than attributes in the XSLT namespace), or when it references a non-empty attribute set, the on-empty attribute has no effect because these conditions will not be satisfied.

Example: Generating a Wrapper Element for a non-Empty Sequence

The following example generates an events element if and only if there are one or more event elements. The code could be written like this:

<xsl:if test="exists(event)">
  <events>
    <xsl:copy-of select="event"/>
  </events>
</xsl:if>

However, the above code would not be guaranteed streamable. To make it streamable, it can be rewritten as:

<events xsl:on-empty="()">
    <xsl:copy-of select="event"/>
</events>

Note:

The reason for introducing the on-empty attribute is primarily to make it easier to write applications that conform to the rules for guaranteed streamability. A common requirement is to generate a wrapper element for a sequence of elements (for example an events wrapper for a sequence of event elements) only if the content sequence is non-empty. Without the xsl:on-empty attribute this is difficult to achieve, because testing whether any event element exists and processing the set of event elements both count as consuming instructions.

11.1.5 Namespace Aliasing

When a stylesheet is used to define a transformation whose output is itself a stylesheet module, or in certain other cases where the result document uses namespaces that it would be inconvenient to use in the stylesheet, namespace aliasing can be used to declare a mapping between a namespace URI used in the stylesheet and the corresponding namespace URI to be used in the result document.

[Definition: A namespace URI in the stylesheet tree that is being used to specify a namespace URI in the result tree is called a literal namespace URI.]

[Definition: The namespace URI that is to be used in the result tree as a substitute for a literal namespace URI is called the target namespace URI.]

Either of the literal namespace URI or the target namespace URI can be null: this is treated as a reference to the set of names that are in no namespace.

<!-- Category: declaration -->
<xsl:namespace-alias
  stylesheet-prefix = prefix | "#default"
  result-prefix = prefix | "#default" />

[Definition: A stylesheet can use the xsl:namespace-alias element to declare that a literal namespace URI is being used as an alias for a target namespace URI.]

The effect is that when names in the namespace identified by the literal namespace URI are copied to the result tree, the namespace URI in the result tree will be the target namespace URI, instead of the literal namespace URI. This applies to:

  • the namespace URI in the expanded QName of a literal result element in the stylesheet

  • the namespace URI in the expanded QName of an attribute specified on a literal result element in the stylesheet

The effect of an xsl:namespace-alias declaration is local to the package in which it appears: that is, it only affects the result of literal result elements within the same package.

Where namespace aliasing changes the namespace URI part of the expanded QName containing the name of an element or attribute node, the namespace prefix in that expanded QName is replaced by the prefix indicated by the result-prefix attribute of the xsl:namespace-alias declaration.

The xsl:namespace-alias element declares that the namespace URI bound to the prefix specified by the stylesheet-prefix is the literal namespace URI, and the namespace URI bound to the prefix specified by the result-prefix attribute is the target namespace URI. Thus, the stylesheet-prefix attribute specifies the namespace URI that will appear in the stylesheet, and the result-prefix attribute specifies the corresponding namespace URI that will appear in the result tree.

The default namespace (as declared by xmlns) may be specified by using #default instead of a prefix. If no default namespace is in force, specifying #default denotes the null namespace URI. This allows elements that are in no namespace in the stylesheet to acquire a namespace in the result document, or vice versa.

If a literal namespace URI is declared to be an alias for multiple different target namespace URIs, then the declaration with the highest import precedence is used.

[ERR XTSE0810] It is a static error if within a package there is more than one such declaration with the same literal namespace URI and the same import precedence and different values for the target namespace URI, unless there is also an xsl:namespace-alias declaration with the same literal namespace URI and a higher import precedence.

[ERR XTSE0812] It is a static error if a value other than #default is specified for either the stylesheet-prefix or the result-prefix attributes of the xsl:namespace-alias element when there is no in-scope binding for that namespace prefix.

When a literal result element is processed, its namespace nodes are handled as follows:

In the event that the same URI is used as a literal namespace URI and a target namespace URI, the second of these rules takes precedence.

Note:

These rules achieve the effect that the element generated from the literal result element will have an in-scope namespace node that binds the result-prefix to the target namespace URI, provided that the namespace declaration associating this prefix with this URI is in scope for both the xsl:namespace-alias instruction and for the literal result element. Conversely, the stylesheet-prefix and the literal namespace URI will not normally appear in the result tree.

Example: Using xsl:namespace-alias to Generate a Stylesheet

When literal result elements are being used to create element, attribute, or namespace nodes that use the XSLT namespace URI, the stylesheet may use an alias.

For example, the stylesheet

<xsl:stylesheet
  version="3.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:fo="http://www.w3.org/1999/XSL/Format"
  xmlns:axsl="file://namespace.alias">

<xsl:namespace-alias stylesheet-prefix="axsl" result-prefix="xsl"/>

<xsl:template match="/">
  <axsl:stylesheet version="3.0">
    <xsl:apply-templates/>
  </axsl:stylesheet>
</xsl:template>

<xsl:template match="elements">
  <axsl:template match="/">
     <axsl:comment select="system-property('xsl:version')"/>
     <axsl:apply-templates/>
  </axsl:template>
</xsl:template>

<xsl:template match="block">
  <axsl:template match="{.}">
     <fo:block><axsl:apply-templates/></fo:block>
  </axsl:template>
</xsl:template>

</xsl:stylesheet>

will generate an XSLT stylesheet from a document of the form:

<elements>
<block>p</block>
<block>h1</block>
<block>h2</block>
<block>h3</block>
<block>h4</block>
</elements>

The output of the transformation will be a stylesheet such as the following. Whitespace has been added for clarity. Note that an implementation may output different namespace prefixes from those appearing in this example; however, the rules guarantee that there will be a namespace node that binds the prefix xsl to the URI http://www.w3.org/1999/XSL/Transform, which makes it safe to use the QName xsl:version in the content of the generated stylesheet.

<xsl:stylesheet
  version="3.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
  xmlns:fo="http://www.w3.org/1999/XSL/Format">

<xsl:template match="/">
  <xsl:comment select="system-property('xsl:version')"/>
  <xsl:apply-templates/>
</xsl:template>
  
<xsl:template match="p">
  <fo:block><xsl:apply-templates/></fo:block>
</xsl:template>

<xsl:template match="h1">
  <fo:block><xsl:apply-templates/></fo:block>
</xsl:template>

<xsl:template match="h2">
  <fo:block><xsl:apply-templates/></fo:block>
</xsl:template>

<xsl:template match="h3">
  <fo:block><xsl:apply-templates/></fo:block>
</xsl:template>

<xsl:template match="h4">
  <fo:block><xsl:apply-templates/></fo:block>
</xsl:template>

</xsl:stylesheet>

Note:

It may be necessary also to use aliases for namespaces other than the XSLT namespace URI. For example, it can be useful to define an alias for the namespace http://www.w3.org/2001/XMLSchema-instance, so that the stylesheet can use the attributes xsi:type, xsi:nil, and xsi:schemaLocation on a literal result element, without running the risk that a schema processor will interpret these as applying to the stylesheet itself. Equally, literal result elements belonging to a namespace dealing with digital signatures might cause XSLT stylesheets to be mishandled by general-purpose security software; using an alias for the namespace would avoid the possibility of such mishandling.

Example: Aliasing the XML Namespace

It is possible to define an alias for the XML namespace.

<xsl:stylesheet xmlns:axml="http://www.example.com/alias-xml"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                version="3.0">

<xsl:namespace-alias stylesheet-prefix="axml" result-prefix="xml"/>

<xsl:template match="/">
  <name axml:space="preserve">
    <first>James</first>
    <xsl:text> </xsl:text>
    <last>Clark</last>
  </name>
</xsl:template>

</xsl:stylesheet>

produces the output:

<name xml:space="preserve"><first>James</first> <last>Clark</last></name>

This allows an xml:space attribute to be generated in the output without affecting the way the stylesheet is parsed. The same technique can be used for other attributes such as xml:lang, xml:base, and xml:id.

Note:

Namespace aliasing is only necessary when literal result elements are used. The problem of reserved namespaces does not arise when using xsl:element and xsl:attribute to construct the result tree. Therefore, as an alternative to using xsl:namespace-alias, it is always possible to achieve the desired effect by replacing literal result elements with xsl:element and xsl:attribute instructions.

11.2 Creating Element Nodes Using xsl:element

<!-- Category: instruction -->
<xsl:element
  name = { qname }
  namespace? = { uri }
  inherit-namespaces? = "yes" | "no"
  use-attribute-sets? = eqnames
  type? = eqname
  validation? = "strict" | "lax" | "preserve" | "strip"
  on-empty? = expression >
  <!-- Content: sequence-constructor -->
</xsl:element>

The xsl:element instruction allows an element to be created with a computed name. The expanded QName of the element to be created is specified by a required name attribute and an optional namespace attribute.

The result of evaluating the xsl:element instruction, in usual circumstances, is the newly constructed element node.

11.2.1 The Content of the Constructed Element Node

The content of the xsl:element instruction is a sequence constructor for the children, attributes, and namespaces of the created element. The sequence obtained by evaluating this sequence constructor (see 5.8 Sequence Constructors) is used to construct the content of the element, as described in 5.8.1 Constructing Complex Content.

The xsl:element element may have a use-attribute-sets attribute, whose value is a whitespace-separated list of QNames that identify xsl:attribute-set declarations. If this attribute is present, it is expanded as described in 10.2 Named Attribute Sets to produce a sequence of attribute nodes. This sequence is prepended to the sequence produced as a result of evaluating the sequence constructor, as described in 5.8.1 Constructing Complex Content.

11.2.2 The Name of the Constructed Element Node

The name attribute is interpreted as an attribute value template, whose effective value must be a lexical QName.

[ERR XTDE0820] It is a dynamic error if the effective value of the name attribute is not a lexical QName.

[ERR XTDE0830] In the case of an xsl:element instruction with no namespace attribute, it is a dynamic error if the effective value of the name attribute is a lexical QName whose prefix is not declared in an in-scope namespace declaration for the xsl:element instruction.

If the namespace attribute is not present then the lexical QName is expanded into an expanded QName using the namespace declarations in effect for the xsl:element element, including any default namespace declaration.

If the namespace attribute is present, then it too is interpreted as an attribute value template. The effective value must be in the lexical space of the xs:anyURI type. If the string is zero-length, then the expanded QName of the element has a null namespace URI. Otherwise, the string is used as the namespace URI of the expanded QName of the element to be created. The local part of the lexical QName specified by the name attribute is used as the local part of the expanded QName of the element to be created.

[ERR XTDE0835] It is a dynamic error if the effective value of the namespace attribute is not in the lexical space of the xs:anyURI datatype or if it is the string http://www.w3.org/2000/xmlns/.

Note:

The XDM data model requires the name of a node to be an instance of xs:QName, and XML Schema defines the namespace part of an xs:QName to be an instance of xs:anyURI. However, the schema specification, and the specifications that it refers to, give implementations some flexibility in how strictly they enforce these constraints.

The prefix of the lexical QName specified in the name attribute (or the absence of a prefix) is copied to the prefix part of the expanded QName representing the name of the new element node. In the event of a conflict a prefix may subsequently be added, changed, or removed during the namespace fixup process (see 5.8.3 Namespace Fixup). The term conflict here means any violation of the constraints defined in [Data Model], for example the use of the same prefix to refer to two different namespaces in the element and in one of its attributes, the use of the prefix xml to refer to a namespace other than the XML namespace, or any use of the prefix xmlns.

11.2.3 Other Properties of the Constructed Element Node

The xsl:element instruction has an optional inherit-namespaces attribute, with the value yes or no. The default value is yes. If the value is set to yes, or is omitted, then the namespace nodes created for the newly constructed element (whether these were copied from those of the source node, or generated as a result of namespace fixup) are copied to the children and descendants of the newly constructed element, as described in 5.8.1 Constructing Complex Content. If the value is set to no, then these namespace nodes are not automatically copied to the children. This may result in namespace undeclarations (such as xmlns="" or, in the case of XML Namespaces 1.1, xmlns:p="") appearing on the child elements when a final result tree is serialized.

The base URI of the new element is copied from the base URI of the xsl:element instruction in the stylesheet, unless the content of the new element includes an xml:base attribute, in which case the base URI of the new element is the value of that attribute, resolved (if it is a relative URI) against the base URI of the xsl:element instruction in the stylesheet. (Note, however, that this is only relevant when creating parentless elements. When the new element is copied to form a child of an element or document node, the base URI of the new copy is taken from that of its new parent.)

11.2.4 The Type Annotation of the Constructed Element Node

The optional attributes type and validation may be used on the xsl:element instruction to invoke validation of the contents of the element against a type definition or element declaration in a schema, and to determine the type annotation that the new element node will carry. These attributes also affect the type annotation carried by any elements and attributes that have the new element node as an ancestor. These two attributes are both optional, and if one is specified then the other must be omitted. The permitted values of these attributes and their semantics are described in 24.2 Validation.

Note:

The final type annotation of the element in the result tree also depends on the type and validation attributes of the instructions used to create the ancestors of the element.

11.2.5 Conditional Construction of Element Nodes

If the on-empty attribute is present and the content of the constructed element as determined by the rules in 11.2.1 The Content of the Constructed Element Node (that is, the result of evaluating the sequence constructor and prepending any attributes generated by the use-attribute-sets attribute) is a sequence containing nothing other than namespace nodes and zero-length text nodes, then instead of returning the newly constructed element node, the instruction returns the result of evaluating the expression in the on-empty attribute; if this expression returns a node, the instruction returns a copy of this node.

[ERR XTTE3310] It is a type error if the result of evaluating the on-empty attribute does not satisfy the required type element()?. That is, the expression must deliver either a single element node, or an empty sequence.

If the on-empty expression is evaluated and returns an empty sequence, then the validation and type attributes are ignored. However, if the result of the on-empty expression is an element, then it is subjected to validation as determined by these attributes, along with [xsl:]default-validation where relevant.

11.3 Creating Attribute Nodes Using xsl:attribute

<!-- Category: instruction -->
<xsl:attribute
  name = { qname }
  namespace? = { uri }
  select? = expression
  separator? = { string }
  type? = eqname
  validation? = "strict" | "lax" | "preserve" | "strip"
  on-empty? = expression >
  <!-- Content: sequence-constructor -->
</xsl:attribute>

The xsl:attribute element can be used to add attributes to result elements whether created by literal result elements in the stylesheet or by instructions such as xsl:element or xsl:copy. The expanded QName of the attribute to be created is specified by a required name attribute and an optional namespace attribute. Except in error cases, the result of evaluating an xsl:attribute instruction is the newly constructed attribute node.

The string value of the new attribute node may be defined either by using the select attribute, or by the sequence constructor that forms the content of the xsl:attribute element. These are mutually exclusive: if the select attribute is present then the sequence constructor must be empty, and if the sequence constructor is non-empty then the select attribute must be absent. If the select attribute is absent and the sequence constructor is empty, then the string value of the new attribute node will be a zero-length string. The way in which the value is constructed is specified in 5.8.2 Constructing Simple Content.

[ERR XTSE0840] It is a static error if the select attribute of the xsl:attribute element is present unless the element has empty content.

If the separator attribute is present, then the effective value of this attribute is used to separate adjacent items in the result sequence, as described in 5.8.2 Constructing Simple Content. In the absence of this attribute, the default separator is a single space (#x20) when the content is specified using the select attribute, or a zero-length string when the content is specified using a sequence constructor.

The name attribute is interpreted as an attribute value template, whose effective value must be a lexical QName.

[ERR XTDE0850] It is a dynamic error if the effective value of the name attribute is not a lexical QName.

[ERR XTDE0855] In the case of an xsl:attribute instruction with no namespace attribute, it is a dynamic error if the effective value of the name attribute is the string xmlns.

[ERR XTDE0860] In the case of an xsl:attribute instruction with no namespace attribute, it is a dynamic error if the effective value of the name attribute is a lexical QName whose prefix is not declared in an in-scope namespace declaration for the xsl:attribute instruction.

If the namespace attribute is not present, then the lexical QName is expanded into an expanded QName using the namespace declarations in effect for the xsl:attribute element, not including any default namespace declaration.

If the namespace attribute is present, then it too is interpreted as an attribute value template. The effective value must be in the lexical space of the xs:anyURI type. If the string is zero-length, then the expanded QName of the attribute has a null namespace URI. Otherwise, the string is used as the namespace URI of the expanded QName of the attribute to be created. The local part of the lexical QName specified by the name attribute is used as the local part of the expanded QName of the attribute to be created.

[ERR XTDE0865] It is a dynamic error if the effective value of the namespace attribute is not in the lexical space of the xs:anyURI datatype or if it is the string http://www.w3.org/2000/xmlns/.

Note:

The same considerations apply as for elements: [see ERR XTDE0835] in 11.2 Creating Element Nodes Using xsl:element .

The prefix of the lexical QName specified in the name attribute (or the absence of a prefix) is copied to the prefix part of the expanded QName representing the name of the new attribute node. In the event of a conflict this prefix may subsequently be added, changed, or removed during the namespace fixup process (see 5.8.3 Namespace Fixup). If the attribute is in a non-null namespace and no prefix is specified, then the namespace fixup process will invent a prefix. The term conflict here means any violation of the constraints defined in [Data Model], for example the use of the same prefix to refer to two different namespaces in the element and in one of its attributes, the use of the prefix xml to refer to a namespace other than the XML namespace, or any use of the prefix xmlns.

If the name of a constructed attribute is xml:id, the processor must perform attribute value normalization by effectively applying the normalize-spaceFO30 function to the value of the attribute, and the resulting attribute node must be given the is-id property. This applies whether the attribute is constructed using the xsl:attribute instruction or whether it is constructed using an attribute of a literal result element. This does not imply any constraints on the value of the attribute, or on its uniqueness, and it does not affect the type annotation of the attribute, unless the containing document is validated.

Note:

The effect of setting the is-id property is that the parent element can be located within the containing document by use of the idFO30 function. In effect, XSLT when constructing a document performs some of the functions of an xml:id processor, as defined in [xml:id]; the other aspects of xml:id processing are performed during validation.

Example: Creating a List-Valued Attribute

The following instruction creates the attribute colors="red green blue":

<xsl:attribute name="colors" select="'red', 'green', 'blue'"/>

 

Example: Namespaces are not Attributes

It is not an error to write:

<xsl:attribute name="xmlns:xsl" 
   namespace="file://some.namespace"
   select="'http://www.w3.org/1999/XSL/Transform'"/>

However, this will not result in the namespace declaration xmlns:xsl="http://www.w3.org/1999/XSL/Transform" being output. Instead, it will produce an attribute node with local name xsl, and with a system-allocated namespace prefix mapped to the namespace URI file://some.namespace. This is because the namespace fixup process is not allowed to use xmlns as the name of a namespace node.

As described in 5.8.1 Constructing Complex Content, in a sequence that is used to construct the content of an element, any attribute nodes must appear in the sequence before any element, text, comment, or processing instruction nodes. Where the sequence contains two or more attribute nodes with the same expanded QName, the one that comes last is the only one that takes effect.

Note:

If a collection of attributes is generated repeatedly, this can be done conveniently by using named attribute sets: see 10.2 Named Attribute Sets

11.3.1 Setting the Type Annotation for a Constructed Attribute Node

The optional attributes type and validation may be used on the xsl:attribute instruction to invoke validation of the contents of the attribute against a type definition or attribute declaration in a schema, and to determine the type annotation that the new attribute node will carry. These two attributes are both optional, and if one is specified then the other must be omitted. The permitted values of these attributes and their semantics are described in 24.2 Validation.

Note:

The final type annotation of the attribute in the result tree also depends on the type and validation attributes of the instructions used to create the ancestors of the attribute.

11.3.2 Conditional Creation of Attribute Nodes

If the on-empty attribute is present and the string value of the constructed attribute is a zero-length string, then instead of returning the constructed attribute, the instruction returns the result of evaluating the expression in the on-empty attribute; if this expression returns a node, the instruction returns a copy of the node..

[ERR XTTE3320] It is a type error if the result of evaluating the on-empty attribute does not satisfy the required type attribute()?. That is, the expression must deliver either a single attribute node, or an empty sequence.

If the on-empty expression is evaluated and returns an empty sequence, then the validation and type attributes are ignored. However, if the result of the on-empty expression is an attribute node, then it is subjected to validation as determined by these attributes, along with [xsl:]default-validation where relevant.

11.4 Creating Text Nodes

This section describes three different ways of creating text nodes: by means of literal text nodes in the stylesheet, or by using the xsl:text and xsl:value-of instructions. It is also possible to create text nodes using the xsl:number instruction described in 12 Numbering.

If and when the sequence that results from evaluating a sequence constructor is used to form the content of a node, as described in 5.8.2 Constructing Simple Content and 5.8.1 Constructing Complex Content, adjacent text nodes in the sequence are merged. Within the sequence itself, however, they exist as distinct nodes.

Example: A Sequence of Text Nodes

The following function returns a sequence of three text nodes:

<xsl:function name="f:wrap">
  <xsl:param name="s"/>
  <xsl:text>(</xsl:text>
  <xsl:value-of select="$s"/>
  <xsl:text>)</xsl:text>
</xsl:function>

When this function is called as follows:

<xsl:value-of select="f:wrap('---')"/>

the result is:

(---)

No additional spaces are inserted, because the calling xsl:value-of instruction merges adjacent text nodes before atomizing the sequence. However, the result of the instruction:

<xsl:value-of select="data(f:wrap('---'))"/>

is:

( --- )

because in this case the three text nodes are atomized to form three strings, and spaces are inserted between adjacent strings.

It is possible to construct text nodes whose string value is zero-length. A zero-length text node, when atomized, produces a zero-length string. However, zero-length text nodes are ignored when they appear in a sequence that is used to form the content of a node, as described in 5.8.1 Constructing Complex Content and 5.8.2 Constructing Simple Content.

11.4.1 Literal Text Nodes

A sequence constructor can contain text nodes. Each text node in a sequence constructor remaining after whitespace text nodes have been stripped as specified in 4.2 Stripping Whitespace from the Stylesheet will construct a new text node with the same string value. The resulting text node is added to the result of the containing sequence constructor.

Text is processed at the tree level. Thus, markup of &lt; in a template will be represented in the stylesheet tree by a text node that includes the character <. This will create a text node in the result tree that contains a < character, which will be represented by the markup &lt; (or an equivalent character reference) when the result tree is serialized as an XML document, unless otherwise specified using character maps (see 25.1 Character Maps) or disable-output-escaping (see 25.2 Disabling Output Escaping).

11.4.2 Creating Text Nodes Using xsl:text

<!-- Category: instruction -->
<xsl:text
  [disable-output-escaping]? = "yes" | "no" >
  <!-- Content: #PCDATA -->
</xsl:text>

The xsl:text element is evaluated to construct a new text node. The content of the xsl:text element is a single text node whose value forms the string value of the new text node. An xsl:text element may be empty, in which case the result of evaluating the instruction is a text node whose string value is the zero-length string.

The result of evaluating an xsl:text instruction is the newly constructed text node.

A text node that is an immediate child of an xsl:text instruction will not be stripped from the stylesheet tree, even if it consists entirely of whitespace (see 4.4 Stripping Whitespace from a Source Tree).

For the effect of the deprecated disable-output-escaping attribute, see 25.2 Disabling Output Escaping

Note:

It is not always necessary to use the xsl:text instruction to write text nodes to the result tree. Literal text can be written to the result tree by including it anywhere in a sequence constructor, while computed text can be output using the xsl:value-of instruction. The principal reason for using xsl:text is that it offers improved control over whitespace handling.

11.4.3 Generating Text with xsl:value-of

Within a sequence constructor, the xsl:value-of instruction can be used to generate computed text nodes. The xsl:value-of instruction computes the text using an expression that is specified as the value of the select attribute, or by means of contained instructions. This might, for example, extract text from a source tree or insert the value of a variable.

<!-- Category: instruction -->
<xsl:value-of
  select? = expression
  separator? = { string }
  [disable-output-escaping]? = "yes" | "no" >
  <!-- Content: sequence-constructor -->
</xsl:value-of>

The xsl:value-of instruction is evaluated to construct a new text node; the result of the instruction is the newly constructed text node.

The string value of the new text node may be defined either by using the select attribute, or by the sequence constructor (see 5.8 Sequence Constructors) that forms the content of the xsl:value-of element. These are mutually exclusive: if the select attribute is present then the sequence constructor must be empty, and if the sequence constructor is non-empty then the select attribute must be absent. If the select attribute is absent and the sequence constructor is empty, then the result of the instruction is a text node whose string value is zero-length. The way in which the value is constructed is specified in 5.8.2 Constructing Simple Content.

[ERR XTSE0870] It is a static error if the select attribute of the xsl:value-of element is present when the content of the element is non-empty

If the separator attribute is present, then the effective value of this attribute is used to separate adjacent items in the result sequence, as described in 5.8.2 Constructing Simple Content. In the absence of this attribute, the default separator is a single space (#x20) when the content is specified using the select attribute, or a zero-length string when the content is specified using a sequence constructor.

Special rules apply when the instruction is processed with XSLT 1.0 behavior. If no separator attribute is present, and if the select attribute is present, then all items in the atomized result sequence other than the first are ignored.

Example: Generating a List with Separators

The instruction:

<x><xsl:value-of select="1 to 4" separator="|"/></x>

produces the output:

<x>1|2|3|4</x>

Note:

The xsl:copy-of element can be used to copy a sequence of nodes to the result tree without atomization. See 11.9.2 Deep Copy.

For the effect of the deprecated disable-output-escaping attribute, see 25.2 Disabling Output Escaping

11.5 Creating Document Nodes

<!-- Category: instruction -->
<xsl:document
  validation? = "strict" | "lax" | "preserve" | "strip"
  type? = eqname >
  <!-- Content: sequence-constructor -->
</xsl:document>

The xsl:document instruction is used to create a new document node. The content of the xsl:document element is a sequence constructor for the children of the new document node. A document node is created, and the sequence obtained by evaluating the sequence constructor is used to construct the content of the document, as described in 5.8.1 Constructing Complex Content. The temporary tree rooted at this document node forms the result tree.

Except in error situations, the result of evaluating the xsl:document instruction is a single node, the newly constructed document node.

Note:

The new document is not serialized. To construct a document that is to form a final result rather than an intermediate result, use the xsl:result-document instruction described in 24.1 Creating Final Result Trees.

The optional attributes type and validation may be used on the xsl:document instruction to validate the contents of the new document, and to determine the type annotation that elements and attributes within the result tree will carry. The permitted values and their semantics are described in 24.2.2 Validating Document Nodes.

The base URI of the new document node is taken from the base URI of the xsl:document instruction.

The document-uri and unparsed-entities properties of the new document node are set to empty.

Example: Checking Uniqueness Constraints in a Temporary Tree

The following example creates a temporary tree held in a variable. The use of an enclosed xsl:document instruction ensures that uniqueness constraints defined in the schema for the relevant elements are checked.

<xsl:variable name="tree" as="document-node()">
  <xsl:document validation="strict">
    <xsl:apply-templates/>
  </xsl:document>
</xsl:variable>

11.6 Creating Processing Instructions

<!-- Category: instruction -->
<xsl:processing-instruction
  name = { ncname }
  select? = expression >
  <!-- Content: sequence-constructor -->
</xsl:processing-instruction>

The xsl:processing-instruction element is evaluated to create a processing instruction node.

The xsl:processing-instruction element has a required name attribute that specifies the name of the processing instruction node. The value of the name attribute is interpreted as an attribute value template.

The string value of the new processing-instruction node may be defined either by using the select attribute, or by the sequence constructor that forms the content of the xsl:processing-instruction element. These are mutually exclusive: if the select attribute is present then the sequence constructor must be empty, and if the sequence constructor is non-empty then the select attribute must be absent. If the select attribute is absent and the sequence constructor is empty, then the string value of the new processing-instruction node will be a zero-length string. The way in which the value is constructed is specified in 5.8.2 Constructing Simple Content.

[ERR XTSE0880] It is a static error if the select attribute of the xsl:processing-instruction element is present unless the element has empty content.

Except in error situations, the result of evaluating the xsl:processing-instruction instruction is a single node, the newly constructed processing instruction node.

Example: Creating a Processing Instruction

This instruction:

<xsl:processing-instruction name="xml-stylesheet"
  select="('href=&quot;book.css&quot;', 'type=&quot;text/css&quot;')"/>

creates the processing instruction

<?xml-stylesheet href="book.css" type="text/css"?>

Note that the xml-stylesheet processing instruction contains pseudo-attributes in the form name="value". Although these have the same textual form as attributes in an element start tag, they are not represented as XDM attribute nodes, and cannot therefore be constructed using xsl:attribute instructions.

[ERR XTDE0890] It is a dynamic error if the effective value of the name attribute is not both an NCNameNames and a PITargetXML.

Note:

Because these rules disallow the name xml, the xsl:processing-instruction cannot be used to output an XML declaration. The xsl:output declaration should be used to control this instead (see 25 Serialization).

If the result of evaluating the content of the xsl:processing-instruction contains the string ?>, this string is modified by inserting a space between the ? and > characters.

The base URI of the new processing-instruction is copied from the base URI of the xsl:processing-instruction element in the stylesheet. (Note, however, that this is only relevant when creating a parentless processing instruction. When the new processing instruction is copied to form a child of an element or document node, the base URI of the new copy is taken from that of its new parent.)

11.7 Creating Namespace Nodes

<!-- Category: instruction -->
<xsl:namespace
  name = { ncname }
  select? = expression >
  <!-- Content: sequence-constructor -->
</xsl:namespace>

The xsl:namespace element is evaluated to create a namespace node. Except in error situations, the result of evaluating the xsl:namespace instruction is a single node, the newly constructed namespace node.

The xsl:namespace element has a required name attribute that specifies the name of the namespace node (that is, the namespace prefix). The value of the name attribute is interpreted as an attribute value template. If the effective value of the name attribute is a zero-length string, a namespace node is added for the default namespace.

The string value of the new namespace node (that is, the namespace URI) may be defined either by using the select attribute, or by the sequence constructor that forms the content of the xsl:namespace element. These are mutually exclusive: if the select attribute is present then the sequence constructor must be empty, and if the sequence constructor is non-empty then the select attribute must be absent. Since the string value of a namespace node cannot be a zero-length string, either a select attribute or a non-empty sequence constructor must be present. The way in which the value is constructed is specified in 5.8.2 Constructing Simple Content.

[ERR XTDE0905] It is a dynamic error if the string value of the new namespace node is not valid in the lexical space of the datatype xs:anyURI, or if it is the string http://www.w3.org/2000/xmlns/.

[ERR XTSE0910] It is a static error if the select attribute of the xsl:namespace element is present when the element has content other than one or more xsl:fallback instructions, or if the select attribute is absent when the element has empty content.

Note the restrictions described in 5.8.1 Constructing Complex Content for the position of a namespace node relative to other nodes in the node sequence returned by a sequence constructor.

Example: Constructing a QName-Valued Attribute

This literal result element:

<data xsi:type="xs:integer" 
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <xsl:namespace name="xs" 
                 select="'http://www.w3.org/2001/XMLSchema'"/>
  <xsl:text>42</xsl:text>
</data>

would typically cause the output document to contain the element:

<data xsi:type="xs:integer"
     xmlns:xs="http://www.w3.org/2001/XMLSchema"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">42</data>

In this case, the element is constructed using a literal result element, and the namespace xmlns:xs="http://www.w3.org/2001/XMLSchema" could therefore have been added to the result tree simply by declaring it as one of the in-scope namespaces in the stylesheet. In practice, the xsl:namespace instruction is more likely to be useful in situations where the element is constructed using an xsl:element instruction, which does not copy all the in-scope namespaces from the stylesheet.

[ERR XTDE0920] It is a dynamic error if the effective value of the name attribute is neither a zero-length string nor an NCNameNames, or if it is xmlns.

[ERR XTDE0925] It is a dynamic error if the xsl:namespace instruction generates a namespace node whose name is xml and whose string value is not http://www.w3.org/XML/1998/namespace, or a namespace node whose string value is http://www.w3.org/XML/1998/namespace and whose name is not xml.

[ERR XTDE0930] It is a dynamic error if evaluating the select attribute or the contained sequence constructor of an xsl:namespace instruction results in a zero-length string.

For details of other error conditions that may arise, see 5.8 Sequence Constructors.

Note:

It is rarely necessary to use xsl:namespace to create a namespace node in the result tree; in most circumstances, the required namespace nodes will be created automatically, as a side-effect of writing elements or attributes that use the namespace. An example where xsl:namespace is needed is a situation where the required namespace is used only within attribute values in the result document, not in element or attribute names; especially where the required namespace prefix or namespace URI is computed at run-time and is not present in either the source document or the stylesheet.

Adding a namespace node to the result tree will never change the expanded QName of any element or attribute node in the result tree: that is, it will never change the namespace URI of an element or attribute. It might, however, constrain the choice of prefixes when namespace fixup is performed.

Namespace prefixes for element and attribute names are initially established by the rules of the instruction that creates the element or attribute node, and in the event of conflicts, they may be changed by the namespace fixup process described in 5.8.3 Namespace Fixup. The fixup process ensures that an element has in-scope namespace nodes for the namespace URIs used in the element name and in its attribute names, and the serializer will typically use these namespace nodes to determine the prefix to use in the serialized output. The fixup process cannot generate namespace nodes that are inconsistent with those already present in the tree. This means that it is not possible for the processor to decide the prefix to use for an element or for any of its attributes until all the namespace nodes for the element have been added.

If a namespace prefix is mapped to a particular namespace URI using the xsl:namespace instruction, or by using xsl:copy or xsl:copy-of to copy a namespace node, this prevents the namespace fixup process (and hence the serializer) from using the same prefix for a different namespace URI on the same element.

Example: Conflicting Namespace Prefixes

Given the instruction:

<xsl:element name="p:item" 
                 xmlns:p="http://www.example.com/p">
  <xsl:namespace name="p">http://www.example.com/q</xsl:namespace>
</xsl:element>

a possible serialization of the result tree is:

<ns0:item 
    xmlns:ns0="http://www.example.com/p" 
    xmlns:p="http://www.example.com/q"/>

The processor must invent a namespace prefix for the URI p.uri; it cannot use the prefix p because that prefix has been explicitly associated with a different URI.

Note:

The xsl:namespace instruction cannot be used to generate a namespace undeclaration of the form xmlns="" (nor the new forms of namespace undeclaration permitted in [Namespaces in XML 1.1]). Namespace undeclarations are generated automatically by the serializer if undeclare-prefixes="yes" is specified on xsl:output, whenever a parent element has a namespace node for the default namespace prefix, and a child element has no namespace node for that prefix.

11.8 Creating Comments

<!-- Category: instruction -->
<xsl:comment
  select? = expression >
  <!-- Content: sequence-constructor -->
</xsl:comment>

The xsl:comment element is evaluated to construct a new comment node. Except in error cases, the result of evaluating the xsl:comment instruction is a single node, the newly constructed comment node.

The string value of the new comment node may be defined either by using the select attribute, or by the sequence constructor that forms the content of the xsl:comment element. These are mutually exclusive: if the select attribute is present then the sequence constructor must be empty, and if the sequence constructor is non-empty then the select attribute must be absent. If the select attribute is absent and the sequence constructor is empty, then the string value of the new comment node will be a zero-length string. The way in which the value is constructed is specified in 5.8.2 Constructing Simple Content.

[ERR XTSE0940] It is a static error if the select attribute of the xsl:comment element is present unless the element has empty content.

Example: Generating a Comment Node

For example, this

<xsl:comment>This file is automatically generated. Do not edit!</xsl:comment>

would create the comment

<!--This file is automatically generated. Do not edit!-->

In the generated comment node, the processor must insert a space after any occurrence of - that is followed by another - or that ends the comment.

11.9 Copying Nodes

11.9.1 Shallow Copy

<!-- Category: instruction -->
<xsl:copy
  select? = expression
  copy-namespaces? = "yes" | "no"
  inherit-namespaces? = "yes" | "no"
  use-attribute-sets? = eqnames
  type? = eqname
  validation? = "strict" | "lax" | "preserve" | "strip"
  on-empty? = expression >
  <!-- Content: sequence-constructor -->
</xsl:copy>

The xsl:copy instruction provides a way of copying a selected item. The selected item is the item selected by evaluating the expression in the select attribute if present, or the context item otherwise. If the selected item is a node, evaluating the xsl:copy instruction constructs a copy of the selected node, and the result of the xsl:copy instruction is this newly constructed node. By default, the namespace nodes of the context node are automatically copied as well, but the attributes and children of the node are not automatically copied.

When the selected item is an atomic value or function item, the xsl:copy instruction returns this value. The sequence constructor is not evaluated, and must not generate any type errors.

When the selected item is an attribute node, text node, comment node, processing instruction node, or namespace node, the xsl:copy instruction returns a new node that is a copy of the context node. The new node will have the same node kind, name, and string value as the context node. In the case of an attribute node, it will also have the same values for the is-id and is-idrefs properties. The sequence constructor is not evaluated, and must not generate any type errors..

When the selected item is a document node or element node, the xsl:copy instruction returns a new node that has the same node kind and name as the selected node. The content of the new node is formed by evaluating the sequence constructor contained in the xsl:copy instruction. If the select attribute is present then the sequence constructor is evaluated with the selected item as the singleton focus; otherwise it is evaluated using the context of the xsl:copy instruction unchanged. The sequence obtained by evaluating this sequence constructor is used (after prepending any attribute nodes or namespace nodes as described in the following paragraphs) to construct the content of the document or element node, as described in 5.8.1 Constructing Complex Content.

If the select expression returns an empty sequence, the xsl:copy instruction returns an empty sequence, and the contained sequence constructor is not evaluated.

[ERR XTTE3180] It is a type error if the result of evaluating the select expression is a sequence of more than one item.

The xsl:copy instruction has an optional use-attribute-sets attribute, whose value is a whitespace-separated list of QNames that identify xsl:attribute-set declarations. This attribute is used only when copying element nodes. This list is expanded as described in 10.2 Named Attribute Sets to produce a sequence of attribute nodes. This sequence is prepended to the sequence produced as a result of evaluating the sequence constructor.

The xsl:copy instruction has an optional copy-namespaces attribute, with the value yes or no. The default value is yes. The attribute is used only when copying element nodes. If the value is set to yes, or is omitted, then all the namespace nodes of the source element are copied as namespace nodes for the result element. These copied namespace nodes are prepended to the sequence produced as a result of evaluating the sequence constructor (it is immaterial whether they come before or after any attribute nodes produced by expanding the use-attribute-sets attribute). If the value is set to no, then the namespace nodes are not copied. However, namespace nodes will still be added to the result element as required by the namespace fixup process: see 5.8.3 Namespace Fixup.

The xsl:copy instruction has an optional inherit-namespaces attribute, with the value yes or no. The default value is yes. The attribute is used only when copying element nodes. If the value is set to yes, or is omitted, then the namespace nodes created for the newly constructed element (whether these were copied from those of the source node, or generated as a result of namespace fixup) are copied to the children and descendants of the newly constructed element, as described in 5.8.1 Constructing Complex Content. If the value is set to no, then these namespace nodes are not automatically copied to the children. This may result in namespace undeclarations (such as xmlns="" or, in the case of XML Namespaces 1.1, xmlns:p="") appearing on the child elements when a final result tree is serialized.

[ERR XTTE0950] It is a type error to use the xsl:copy or xsl:copy-of instruction to copy a node that has namespace-sensitive content if the copy-namespaces attribute has the value no and its explicit or implicit validation attribute has the value preserve. It is also a type error if either of these instructions (with validation="preserve") is used to copy an attribute having namespace-sensitive content, unless the parent element is also copied. A node has namespace-sensitive content if its typed value contains an item of type xs:QName or xs:NOTATION or a type derived therefrom. The reason this is an error is because the validity of the content depends on the namespace context being preserved.

Note:

When attribute nodes are copied, whether with xsl:copy or with xsl:copy-of, the processor does not automatically copy any associated namespace information. The namespace used in the attribute name itself will be declared by virtue of the namespace fixup process (see 5.8.3 Namespace Fixup) when the attribute is added to an element in the result tree, but if namespace prefixes are used in the content of the attribute (for example, if the value of the attribute is an XPath expression) then it is the responsibility of the stylesheet author to ensure that suitable namespace nodes are added to the result tree. This can be achieved by copying the namespace nodes using xsl:copy, or by generating them using xsl:namespace.

The optional attributes type and validation may be used on the xsl:copy instruction to validate the contents of an element, attribute or document node against a type definition, element declaration, or attribute declaration in a schema, and thus to determine the type annotation that the new copy of an element or attribute node will carry. These attributes are ignored when copying an item that is not an element, attribute or document node. When the node being copied is an element or document node, these attributes also affect the type annotation carried by any elements and attributes that have the copied element or document node as an ancestor. These two attributes are both optional, and if one is specified then the other must be omitted. The permitted values of these attributes and their semantics are described in 24.2 Validation.

Note:

The final type annotation of the node in the result tree also depends on the type and validation attributes of the instructions used to create the ancestors of the node.

The base URI of a node is copied, except in the case of an element node having an xml:base attribute, in which case the base URI of the new node is taken as the value of the xml:base attribute, resolved if it is relative against the base URI of the xsl:copy instruction. If the copied node is subsequently attached as a child to a new element or document node, the final copy of the node inherits its base URI from its parent node, unless this is overridden using an xml:base attribute.

When an xml:id attribute is copied, using either the xsl:copy or xsl:copy-of instruction, it is implementation-defined whether the value of the attribute is subjected to attribute value normalization (that is, effectively applying the normalize-spaceFO30 function).

Note:

In most cases the value will already have been subjected to attribute value normalization on the source tree, but if this processing has not been performed on the source tree, it is not an error for it to be performed on the result tree.

11.9.1.1 Conditional Copying of Nodes

The effect of specifying an on-empty attribute is as follows.

If the result of the instruction in the absence of the on-empty attribute would be any of the following:

  • An empty sequence

  • An element or document node having no attributes and no children

  • A node of any other kind with a zero-length string value

then instead of returning this result, the instruction returns the result of evaluating the expression in the on-empty attribute; if the result of this expression is a node, the instruction returns a copy of this node.

[ERR XTTE3330] It is a type error if the result of evaluating the on-empty attribute does not satisfy the required type node()?. That is, the expression must deliver either a single node, or an empty sequence.

If the on-empty expression is evaluated and returns an empty sequence, then the validation and type attributes are ignored. However, if the result of the on-empty expression is a node, then it is subjected to validation as determined by these attributes, along with [xsl:]default-validation where relevant.

11.9.2 Deep Copy

<!-- Category: instruction -->
<xsl:copy-of
  select = expression
  copy-namespaces? = "yes" | "no"
  type? = eqname
  validation? = "strict" | "lax" | "preserve" | "strip" />

The xsl:copy-of instruction can be used to construct a copy of a sequence of nodes, atomic values, and/or function items with each new node containing copies of all the children, attributes, and (by default) namespaces of the original node, recursively. The result of evaluating the instruction is a sequence of items corresponding one-to-one with the supplied sequence, and retaining its order.

The required select attribute contains an expression, whose value may be any sequence of nodes, atomic values, and/or function items. The items in this sequence are processed as follows:

  • If the item is an element node, a new element is constructed and appended to the result sequence. The new element will have the same expanded QName as the original, and it will have deep copies of the attribute nodes and children of the element node.

    The new element will also have namespace nodes copied from the original element node, unless they are excluded by specifying copy-namespaces="no". If this attribute is omitted, or takes the value yes, then all the namespace nodes of the original element are copied to the new element. If it takes the value no, then none of the namespace nodes are copied: however, namespace nodes will still be created in the result tree as required by the namespace fixup process: see 5.8.3 Namespace Fixup. This attribute affects all elements copied by this instruction: both elements selected directly by the select expression, and elements that are descendants of nodes selected by the select expression.

    The new element will have the same values of the is-id, is-idrefs, and nilled properties as the original element.

  • If the item is a document node, the instruction adds a new document node to the result sequence; the children of this document node will be one-to-one copies of the children of the original document node (each copied according to the rules for its own node kind).

  • If the item is an attribute or namespace node, or a text node, a comment, or a processing instruction, the same rules apply as with xsl:copy (see 11.9.1 Shallow Copy).

  • If the item is an atomic value or a function item, the value is appended to the result sequence, as with xsl:sequence.

The optional attributes type and validation may be used on the xsl:copy-of instruction to validate the contents of an element, attribute or document node against a type definition, element declaration, or attribute declaration in a schema and thus to determine the type annotation that the new copy of an element or attribute node will carry. These attributes are applied individually to each element, attribute, and document node that is selected by the expression in the select attribute. These attributes are ignored when copying an item that is not an element, attribute or document node.

The specified type and validation apply directly only to elements, attributes and document nodes created as copies of nodes actually selected by the select expression, they do not apply to nodes that are implicitly copied because they have selected nodes as an ancestor. However, these attributes do indirectly affect the type annotation carried by such implicitly copied nodes, as a consequence of the validation process.

These two attributes are both optional, and if one is specified then the other must be omitted. The permitted values of these attributes and their semantics are described in 24.2 Validation.

Errors may occur when copying namespace-sensitive elements or attributes using validation="preserve". [see ERR XTTE0950].

The base URI of a node is copied, except in the case of an element node having an xml:base attribute, in which case the base URI of the new node is taken as the value of the xml:base attribute, resolved if it is relative against the base URI of the xsl:copy-of instruction. If the copied node is subsequently attached as a child to a new element or document node, the final copy of the node inherits its base URI from its parent node, unless this is overridden using an xml:base attribute.

11.10 Constructing Sequences

<!-- Category: instruction -->
<xsl:sequence
  select? = expression >
  <!-- Content: sequence-constructor -->
</xsl:sequence>

The xsl:sequence instruction may be used within a sequence constructor to construct a sequence of nodes, atomic values, and/or function items. This sequence is returned as the result of the instruction. Unlike most other instructions, xsl:sequence can return a sequence containing existing nodes, rather than constructing new nodes. When xsl:sequence is used to select atomic values or function items, the effect is very similar to the xsl:copy-of instruction.

The items comprising the result sequence are evaluated either using the select attribute, or using the contained sequence constructor. These are mutually exclusive; if the instruction has a select attribute, then it must have no children other than xsl:fallback instructions. If there is no select attribute and no contained sequence constructor, the result is an empty sequence.

[ERR XTSE3185] It is a static error if the select attribute of xsl:sequence is present and the instruction has children other than xsl:fallback.

Any contained xsl:fallback instructions are ignored by an XSLT 2.0 or 3.0 processor, but can be used to define fallback behavior for an XSLT 1.0 processor running in forwards compatibility mode.

Example: Constructing a Sequence of Integers

For example, the following code:

<xsl:variable name="values" as="xs:integer*">
    <xsl:sequence select="(1,2,3,4)"/>
    <xsl:sequence select="(8,9,10)"/>
</xsl:variable>
<xsl:value-of select="sum($values)"/>

produces the output: 37

 

Example: Using xsl:for-each to Construct a Sequence

The following code constructs a sequence containing the value of the @price attribute for selected elements (which we assume to be typed as xs:decimal), or a computed price for those elements that have no @price attribute. It then returns the average price:

<xsl:variable name="prices" as="xs:decimal*">
  <xsl:for-each select="//product">
    <xsl:choose>
      <xsl:when test="@price">
        <xsl:sequence select="@price"/>
      </xsl:when>
      <xsl:otherwise>
        <xsl:sequence select="@cost * 1.5"/>
      </xsl:otherwise>
    </xsl:choose>
  </xsl:for-each>
</xsl:variable>
<xsl:value-of select="avg($prices)"/>

Note that the existing @price attributes could equally have been added to the $prices sequence using xsl:copy-of or xsl:value-of. However, xsl:copy-of would create a copy of the attribute node, which is not needed in this situation, while xsl:value-of would create a new text node, which then has to be converted to an xs:decimal. Using xsl:sequence, which in this case atomizes the existing attribute node and adds an xs:decimal atomic value to the result sequence, is a more direct way of achieving the same result.

This example could alternatively be solved at the XPath level:

<xsl:value-of select="avg(//product/(+@price, @cost*1.5)[1])"/>

The apparently redundant + operator is there to atomize the attribute value: the expression on the right hand side of the / operator must not return a sequence containing both nodes and non-nodes (atomic values or function items).

Note:

The main use case for allowing xsl:sequence to contain a sequence constructor is to allow the instructions within an xsl:fork element to be divided into groups.

It can also be used to limit the scope of local variables or of standard attributes such as [xsl:]default-collation.

12 Numbering

<!-- Category: instruction -->
<xsl:number
  value? = expression
  select? = expression
  level? = "single" | "multiple" | "any"
  count? = pattern
  from? = pattern
  format? = { string }
  lang? = { language }
  letter-value? = { "alphabetic" | "traditional" }
  ordinal? = { string }
  start-at? = { integer }
  grouping-separator? = { char }
  grouping-size? = { integer } />

The xsl:number instruction is used to create a formatted number. The result of the instruction is a newly constructed text node containing the formatted number as its string value.

[Definition: The xsl:number instruction performs two tasks: firstly, determining a place marker (this is a sequence of integers, to allow for hierarchic numbering schemes such as 1.12.2 or 3(c)ii), and secondly, formatting the place marker for output as a text node in the result sequence.] The place marker to be formatted can either be supplied directly, in the value attribute, or it can be computed based on the position of a selected node within the tree that contains it.

[ERR XTSE0975] It is a static error if the value attribute of xsl:number is present unless the select, level, count, and from attributes are all absent.

Note:

The facilities described in this section are specifically designed to enable the calculation and formatting of section numbers, paragraph numbers, and the like. For formatting of other numeric quantities, the format-numberFO30 function may be more suitable: see Section 4.7.2 fn:format-number FO30.

Furthermore, formatting of integers where there is no requirement to calculate the position of a node in the document can now be accomplished using the format-numberFO30 function, which borrows many concepts from the xsl:number specification.

12.1 Formatting a Supplied Number

The place marker to be formatted may be specified by an expression. The value attribute contains the expression. The value of this expression is atomized using the procedure defined in [XPath 3.0], and each value $V in the atomized sequence is then converted to the integer value returned by the XPath expression xs:integer(round(number($V))). If the start-at attribute is present, then its effective value is converted to an integer and decremented by one, and the resulting value is added to each integer in the sequence. The resulting sequence of integers is used as the place marker to be formatted.

If the instruction is processed with XSLT 1.0 behavior, then:

  • all items in the atomized sequence after the first are discarded;

  • If the atomized sequence is empty, it is replaced by a sequence containing the xs:double value NaN as its only item;

  • If any value in the sequence cannot be converted to an integer (this includes the case where the sequence contains a NaN value) then the string NaN is inserted into the formatted result string in its proper position. The error described in the following paragraph does not apply in this case.

[ERR XTDE0980] It is a dynamic error if any undiscarded item in the atomized sequence supplied as the value of the value attribute of xsl:number cannot be converted to an integer, or if the resulting integer is less than 0 (zero).

Note:

The value zero does not arise when numbering nodes in a source document, but it can arise in other numbering sequences. It is permitted specifically because the rules of the xsl:number instruction are also invoked by functions such as format-timeFO30: the minutes and seconds component of a time value can legitimately be zero.

The resulting sequence is formatted as a string using the effective values of the attributes specified in 12.3 Number to String Conversion Attributes; each of these attributes is interpreted as an attribute value template. After conversion, the xsl:number element constructs a new text node containing the resulting string, and returns this node.

Example: Numbering a Sorted List

The following example numbers a sorted list:

<xsl:template match="items">
  <xsl:for-each select="item">
    <xsl:sort select="."/>
    <p>
      <xsl:number value="position()" format="1. "/>
      <xsl:value-of select="."/>
    </p>
  </xsl:for-each>
</xsl:template>

12.2 Numbering based on Position in a Document

If no value attribute is specified, then the xsl:number instruction returns a new text node containing a formatted place marker that is based on the position of a selected node within its containing document. If the select attribute is present, then the expression contained in the select attribute is evaluated to determine the selected node. If the select attribute is omitted, then the selected node is the context node.

[ERR XTTE0990] It is a type error if the xsl:number instruction is evaluated, with no value or select attribute, when the context item is not a node.

[ERR XTTE1000] It is a type error if the result of evaluating the select attribute of the xsl:number instruction is anything other than a single node.

[ERR XTDE1001] It is a dynamic error if the effective value of the start-at attribute of the xsl:number instruction is not in the lexical space of xs:integer. The error may be signaled statically if it can be detected statically.

The following attributes control how the selected node is to be numbered:

  • The level attribute specifies rules for selecting the nodes that are taken into account in allocating a number; it has the values single, multiple or any. The default is single.

  • The count attribute is a pattern that specifies which nodes are to be counted at those levels. If count attribute is not specified, then it defaults to the pattern that matches any node with the same node kind as the selected node and, if the selected node has an expanded QName, with the same expanded QName as the selected node.

  • The from attribute is a pattern that specifies where counting starts.

In addition, the attributes specified in 12.3 Number to String Conversion Attributes are used for number to string conversion, as in the case when the value attribute is specified.

The xsl:number element first constructs a sequence of positive integers using the level, count and from attributes. Where level is single or any, this sequence will either be empty or contain a single number; where level is multiple, the sequence may be of any length. The sequence is constructed as follows:

Let matches-count($node) be a function that returns true if and only if the given node $node matches the pattern given in the count attribute, or the implied pattern (according to the rules given above) if the count attribute is omitted.

Let matches-from($node) be a function that returns true if and only if the given node $node matches the pattern given in the from attribute, or if $node is the root node of a tree. If the from attribute is omitted, then the function returns true if and only if $node is the root node of a tree.

Let $S be the selected node.

When level="single":

  • Let $A be the node sequence selected by the following expression:

       $S/ancestor-or-self::node()[matches-count(.)][1]

    (this selects the innermost ancestor-or-self node that matches the count pattern)

  • Let $F be the node sequence selected by the expression

       $S/ancestor-or-self::node()[matches-from(.)][1]

    (this selects the innermost ancestor-or-self node that matches the from pattern):

  • Let $AF be the value of:

       $A[ancestor-or-self::node()[. is $F]]

    (this selects $A if it is in the subtree rooted at $F, or the empty sequence otherwise)

  • If $AF is empty, return the empty sequence, ()

  • Otherwise return the value of:

       1 + count($AF/preceding-sibling::node()[matches-count(.)])

    (the number of preceding siblings of the counted node that match the count pattern, plus one).

When level="multiple":

  • Let $A be the node sequence selected by the expression

       $S/ancestor-or-self::node()[matches-count(.)]

    (the set of ancestor-or-self nodes that match the count pattern)

  • Let $F be the node sequence selected by the expression

       $S/ancestor-or-self::node()[matches-from(.)][1]

    (the innermost ancestor-or-self node that matches the from pattern)

  • Let $AF be the value of

       $A[ancestor-or-self::node()[. is $F]]

    (the nodes selected in the first step that are in the subtree rooted at the node selected in the second step)

  • Return the result of the expression

       for $af in $AF return 1+count($af/preceding-sibling::node()[matches-count(.)])

    (a sequence of integers containing, for each of these nodes, one plus the number of preceding siblings that match the count pattern)

When level="any":

  • Let $A be the node sequence selected by the expression

       $S/(preceding::node()|ancestor-or-self::node())[matches-count(.)]

    (the set of nodes consisting of the selected node together with all nodes, other than attributes and namespaces, that precede the selected node in document order, provided that they match the count pattern)

  • Let $F be the node sequence selected by the expression

       $S/(preceding::node()|ancestor-or-self::node())[matches-from(.)][last()]

    (the last node in document order that matches the from pattern and that precedes the selected node, using the same definition)

  • Let $AF be the node sequence $A[. is $F or . >> $F].

    (the nodes selected in the first step, excluding those that precede the node selected in the second step)

  • If $AF is empty, return the empty sequence, ()

  • Otherwise return the value of the expression count($AF)

The resulting sequence of numbers is referred to as the place marker).

If the start-at attribute is present, then the effective value of the attribute is converted to an integer and decremented by one, and the resulting value is added to each number in the place marker.

The sequence of numbers (the is then converted into a string using the effective values of the attributes specified in 12.3 Number to String Conversion Attributes; each of these attributes is interpreted as an attribute value template. After conversion, the resulting string is used to create a text node, which forms the result of the xsl:number instruction.

Example: Numbering the Items in an Ordered List

The following will number the items in an ordered list:

<xsl:template match="ol/item">
  <fo:block>
    <xsl:number/>
    <xsl:text>. </xsl:text>
    <xsl:apply-templates/>
  </fo:block>
</xsl:template>

 

Example: Multi-Level Numbering

The following two rules will number title elements. This is intended for a document that contains a sequence of chapters followed by a sequence of appendices, where both chapters and appendices contain sections, which in turn contain subsections. Chapters are numbered 1, 2, 3; appendices are numbered A, B, C; sections in chapters are numbered 1.1, 1.2, 1.3; sections in appendices are numbered A.1, A.2, A.3. Subsections within a chapter are numbered 1.1.1, 1.1.2, 1.1.3; subsections within an appendix are numbered A.1.1, A.1.2, A.1.3.

<xsl:template match="title">
  <fo:block>
     <xsl:number level="multiple"
                 count="chapter|section|subsection"
                 format="1.1 "/>
     <xsl:apply-templates/>
  </fo:block>
</xsl:template>

<xsl:template match="appendix//title" priority="1">
  <fo:block>
     <xsl:number level="multiple"
                 count="appendix|section|subsection"
                 format="A.1 "/>
     <xsl:apply-templates/>
  </fo:block>
</xsl:template>

 

Example: Numbering Notes within a Chapter

This example numbers notes sequentially within a chapter, starting from the number 100: :

<xsl:template match="note">
  <fo:block>
     <xsl:number level="any" from="chapter" format="(1) " start-at="100"/>
     <xsl:apply-templates/>
  </fo:block>
</xsl:template>

12.3 Number to String Conversion Attributes

Note:

This specification is aligned with that of the format-integerFO30 function, but there are differences; for example grouping separators are part of the primary format token in format-integerFO30, but are indicated by separate attributes in xsl:number.

The following attributes are used to control conversion of a sequence of numbers into a string. The numbers are integers greater than or equal to 0 (zero). The attributes are all optional.

The main attribute is format. The default value for the format attribute is 1. The format attribute is split into a sequence of tokens where each token is a maximal sequence of alphanumeric characters or a maximal sequence of non-alphanumeric characters. Alphanumeric means any character that has a Unicode category of Nd, Nl, No, Lu, Ll, Lt, Lm or Lo (see [UNICODE]). The alphanumeric tokens (format tokens) indicate the format to be used for each number in the sequence; in most cases the format token is the same as the required representation of the number 1 (one).

Each non-alphanumeric token is either a prefix, a separator, or a suffix. If there is a non-alphanumeric token but no format token, then the single non-alphanumeric token is used as both the prefix and the suffix. The prefix, if it exists, is the non-alphanumeric token that precedes the first format token: the prefix always appears exactly once in the constructed string, at the start. The suffix, if it exists, is the non-alphanumeric token that follows the last format token: the suffix always appears exactly once in the constructed string, at the end. All other non-alphanumeric tokens (those that occur between two format tokens) are separator tokens and are used to separate numbers in the sequence.

The nth format token is used to format the nth number in the sequence. If there are more numbers than format tokens, then the last format token is used to format remaining numbers. If there are no format tokens, then a format token of 1 is used to format all numbers. Each number after the first is separated from the preceding number by the separator token preceding the format token used to format that number, or, if that is the first format token, then by . (dot).

Example: Formatting a List of Numbers

Given the sequence of numbers 5, 13, 7 and the format token A-001(i), the output will be the string E-013(vii)

Format tokens are interpreted as follows:

  • Any token where the last character has a decimal digit value of 1 (as specified in the Unicode character property database, see [UNICODE]), and the Unicode value of preceding characters is one less than the Unicode value of the last character generates a decimal representation of the number where each number is at least as long as the format token. The digits used in the decimal representation are the set of digits containing the digit character used in the format token. Thus, a format token 1 generates the sequence 0 1 2 ... 10 11 12 ..., and a format token 01 generates the sequence 00 01 02 ... 09 10 11 12 ... 99 100 101. A format token of &#x661; (Arabic-Indic digit one) generates the sequence ١ then ٢ then ٣ ...

  • A format token A generates the sequence A B C ... Z AA AB AC....

  • A format token a generates the sequence a b c ... z aa ab ac....

  • A format token i generates the sequence i ii iii iv v vi vii viii ix x ....

  • A format token I generates the sequence I II III IV V VI VII VIII IX X ....

  • A format token w generates numbers written as lower-case words, for example in English, one two three four ...

  • A format token W generates numbers written as upper-case words, for example in English, ONE TWO THREE FOUR ...

  • A format token Ww generates numbers written as title-case words, for example in English, One Two Three Four ...

  • Any other format token indicates a numbering sequence in which that token represents the number 1 (one) (but see the note below). It is implementation-defined which numbering sequences, additional to those listed above, are supported. If an implementation does not support a numbering sequence represented by the given token, it must use a format token of 1.

    Note:

    In some traditional numbering sequences additional signs are added to denote that the letters should be interpreted as numbers; these are not included in the format token. An example, see also the example below, is classical Greek where a dexia keraia and sometimes an aristeri keraia is added.

For all format tokens other than the first kind above (one that consists of decimal digits), there may be implementation-defined lower and upper bounds on the range of numbers that can be formatted using this format token; indeed, for some numbering sequences there may be intrinsic limits. For example, the formatting token &#x2460; (circled digit one) has a range of 1 to 20 imposed by the Unicode character repertoire. For the numbering sequences described above any upper bound imposed by the implementation must not be less than 1000 (one thousand) and any lower bound must not be greater than 1. Numbers that fall outside this range must be formatted using the format token 1. The numbering sequence associated with the format token 1 has a lower bound of 0 (zero).

The above expansions of numbering sequences for format tokens such as a and i are indicative but not prescriptive. There are various conventions in use for how alphabetic sequences continue when the alphabet is exhausted, and differing conventions for how roman numerals are written (for example, IV versus IIII as the representation of the number 4). Sometimes alphabetic sequences are used that omit letters such as i and o. This specification does not prescribe the detail of any sequence other than those sequences consisting entirely of decimal digits.

Many numbering sequences are language-sensitive. This applies especially to the sequence selected by the tokens w, W and Ww. It also applies to other sequences, for example different languages using the Cyrillic alphabet use different sequences of characters, each starting with the letter #x410 (Cyrillic capital letter A). In such cases, the lang attribute specifies which language's conventions are to be used; it has the same range of values as xml:lang (see [XML 1.0]). If no lang value is specified, the language that is used is implementation-defined. The set of languages for which numbering is supported is implementation-defined. If a language is requested that is not supported, the processor uses the language that it would use if the lang attribute were omitted.

If the optional ordinal attribute is present, and if its value is not a zero-length string, this indicates a request to output ordinal numbers rather than cardinal numbers. For example, in English, the value ordinal="yes" when used with the format token 1 outputs the sequence 1st 2nd 3rd 4th ..., and when used with the format token w outputs the sequence first second third fourth .... In some languages, ordinal numbers vary depending on the grammatical context, for example they may have different genders and may decline with the noun that they qualify. In such cases the value of the ordinal attribute may be used to indicate the variation of the ordinal number required. The way in which the variation is indicated will depend on the conventions of the language. For inflected languages that vary the ending of the word, the preferred approach is to indicate the required ending, preceded by a hyphen: for example in German, appropriate values are -e, -er, -es, -en. It is implementation-defined what combinations of values of the format token, the language, and the ordinal attribute are supported. If ordinal numbering is not supported for the combination of the format token, the language, and the actual value of the ordinal attribute, the request is ignored and cardinal numbers are generated instead.

Example: Ordinal Numbering in Italian

The specification format="1" ordinal="-º" lang="it", if supported, should produce the sequence:

1º 2º 3º 4º ...

The specification format="Ww" ordinal="-o" lang="it", if supported, should produce the sequence:

Primo Secondo Terzo Quarto Quinto ...

The letter-value attribute disambiguates between numbering sequences that use letters. In many languages there are two commonly used numbering sequences that use letters. One numbering sequence assigns numeric values to letters in alphabetic sequence, and the other assigns numeric values to each letter in some other manner traditional in that language. In English, these would correspond to the numbering sequences specified by the format tokens a and i. In some languages, the first member of each sequence is the same, and so the format token alone would be ambiguous. A value of alphabetic specifies the alphabetic sequence; a value of traditional specifies the other sequence. If the letter-value attribute is not specified, then it is implementation-dependent how any ambiguity is resolved.

Note:

Implementations may use extension attributes on xsl:number to provide additional control over the way in which numbers are formatted.

The grouping-separator attribute gives the separator used as a grouping (for example, thousands) separator in decimal numbering sequences, and the optional grouping-size specifies the size (normally 3) of the grouping. For example, grouping-separator="," and grouping-size="3" would produce numbers of the form 1,000,000 while grouping-separator="." and grouping-size="2" would produce numbers of the form 1.00.00.00. If only one of the grouping-separator and grouping-size attributes is specified, then it is ignored.

Example: Format Tokens and the Resulting Sequences

These examples use non-Latin characters which might not display correctly in all browsers, depending on the system configuration.

Description Format Token Sequence
French cardinal words format="Ww" lang="fr" Un, Deux, Trois, Quatre
German ordinal words format="w" ordinal="-e" lang="de" erste, zweite, dritte, vierte
Katakana numbering format="&#x30A2;" ア, イ, ウ, エ, オ, カ, キ, ク, ケ, コ, サ, シ, ス, セ, ソ, タ, チ, ツ, テ, ト, ナ, ニ, ヌ, ネ, ノ, ハ, ヒ, フ, ヘ, ホ, マ, ミ, ム, メ, モ, ヤ, ユ, ヨ, ラ, リ, ル, レ, ロ, ワ, ヰ, ヱ, ヲ, ン
Katakana numbering in iroha order format="&#x30A4;" イ, ロ, ハ, ニ, ホ, ヘ, ト, チ, リ, ヌ, ル, ヲ, ワ, カ, ヨ, タ, レ, ソ, ツ, ネ, ナ, ラ, ム, ウ, ヰ, ノ, オ, ク, ヤ, マ, ケ, フ, コ, エ, テ, ア, サ, キ, ユ, メ, ミ, シ, ヱ, ヒ, モ, セ, ス
Thai numbering format="&#x0E51;" ๑, ๒, ๓, ๔, ๕, ๖, ๗, ๘, ๙, ๑๐, ๑๑, ๑๒, ๑๓, ๑๔, ๑๕, ๑๖, ๑๗, ๑๘, ๑๙, ๒๐
Traditional Hebrew numbering format="&#x05D0;" letter-value="traditional" א, ב, ג, ד, ה, ו, ז, ח, ט, י, יא, יב, יג, יד, טו, טז, יז, יח, יט, כ
Traditional Georgian numbering format="&#x10D0;" letter-value="traditional" ა, ბ, გ, დ, ე, ვ, ზ, ჱ, თ, ი, ია, იბ, იგ, იდ, იე, ივ, იზ, იჱ, ით, კ
Classical Greek numbering (see note) format="&#x03B1;" letter-value="traditional" αʹ, βʹ, γʹ, δʹ, εʹ, ϛʹ, ζʹ, ηʹ, θʹ, ιʹ, ιαʹ, ιβʹ, ιγʹ, ιδʹ, ιεʹ, ιϛʹ, ιζʹ, ιηʹ, ιθʹ, κʹ
Old Slavic numbering format="&#x0430;" letter-value="traditional" А, В, Г, Д, Е, Ѕ, З, И, Ѳ, Ӏ, АӀ, ВӀ, ГӀ, ДӀ, ЕӀ, ЅӀ, ЗӀ, ИӀ, ѲӀ, К

Note that Classical Greek is an example where the format token is not the same as the representation of the number 1.

13 Sorting

[Definition: A sort key specification is a sequence of one or more adjacent xsl:sort elements which together define rules for sorting the items in an input sequence to form a sorted sequence.]

[Definition: Within a sort key specification, each xsl:sort element defines one sort key component.] The first xsl:sort element specifies the primary component of the sort key specification, the second xsl:sort element specifies the secondary component of the sort key specification, and so on.

A sort key specification may occur immediately within an xsl:apply-templates, xsl:for-each, xsl:perform-sort, or xsl:for-each-group element.

Note:

When used within xsl:for-each, xsl:for-each-group, or xsl:perform-sort, xsl:sort elements must occur before any other children.

13.1 The xsl:sort Element

<xsl:sort
  select? = expression
  lang? = { language }
  order? = { "ascending" | "descending" }
  collation? = { uri }
  stable? = { "yes" | "no" }
  case-order? = { "upper-first" | "lower-first" }
  data-type? = { "text" | "number" | eqname } >
  <!-- Content: sequence-constructor -->
</xsl:sort>

The xsl:sort element defines a sort key component. A sort key component specifies how a sort key value is to be computed for each item in the sequence being sorted, and also how two sort key values are to be compared.

The value of a sort key component is determined either by its select attribute or by the contained sequence constructor. If neither is present, the default is select=".", which has the effect of sorting on the actual value of the item if it is an atomic value, or on the typed-value of the item if it is a node. If a select attribute is present, its value must be an XPath expression.

[ERR XTSE1015] It is a static error if an xsl:sort element with a select attribute has non-empty content.

Those attributes of the xsl:sort elements whose values are attribute value templates are evaluated using the same focus as is used to evaluate the select attribute of the containing instruction (specifically, xsl:apply-templates, xsl:for-each, xsl:for-each-group, or xsl:perform-sort).

The stable attribute is permitted only on the first xsl:sort element within a sort key specification

[ERR XTSE1017] It is a static error if an xsl:sort element other than the first in a sequence of sibling xsl:sort elements has a stable attribute.

[Definition: A sort key specification is said to be stable if its first xsl:sort element has no stable attribute, or has a stable attribute whose effective value is yes.]

13.1.1 The Sorting Process

[Definition: The sequence to be sorted is referred to as the initial sequence.]

[Definition: The sequence after sorting as defined by the xsl:sort elements is referred to as the sorted sequence.]

[Definition:  For each item in the initial sequence, a value is computed for each sort key component within the sort key specification. The value computed for an item by using the Nth sort key component is referred to as the Nth sort key value of that item.]

The items in the initial sequence are ordered into a sorted sequence by comparing their sort key values. The relative position of two items A and B in the sorted sequence is determined as follows. The first sort key value of A is compared with the first sort key value of B, according to the rules of the first sort key component. If, under these rules, A is less than B, then A will precede B in the sorted sequence, unless the order attribute of this sort key component specifies descending, in which case B will precede A in the sorted sequence. If, however, the relevant sort key values compare equal, then the second sort key value of A is compared with the second sort key value of B, according to the rules of the second sort key component. This continues until two sort key values are found that compare unequal. If all the sort key values compare equal, and the sort key specification is stable, then A will precede B in the sorted sequence if and only if A preceded B in the initial sequence. If all the sort key values compare equal, and the sort key specification is not stable, then the relative order of A and B in the sorted sequence is implementation-dependent.

Note:

If two items have equal sort key values, and the sort is stable, then their order in the sorted sequence will be the same as their order in the initial sequence, regardless of whether order="descending" was specified on any or all of the sort key components.

The Nth sort key value is computed by evaluating either the select attribute or the contained sequence constructor of the Nth xsl:sort element, or the expression . (dot) if neither is present. This evaluation is done with the focus set as follows:

Note:

As in any other XPath expression, the current function may be used within the select expression of xsl:sort to refer to the item that is the context item for the expression as a whole; that is, the item whose sort key value is being computed.

The sort key values are atomized, and are then compared. The way they are compared depends on their datatype, as described in the next section.

13.1.2 Comparing Sort Key Values

It is possible to force the system to compare sort key values using the rules for a particular datatype by including a cast as part of the sort key component. For example, <xsl:sort select="xs:date(@dob)"/> will force the attributes to be compared as dates. In the absence of such a cast, the sort key values are compared using the rules appropriate to their datatype. Any values of type xs:untypedAtomic are cast to xs:string.

For backwards compatibility with XSLT 1.0, the data-type attribute remains available. If this has the effective value text, the atomized sort key values are converted to strings before being compared. If it has the effective value number, the atomized sort key values are converted to doubles before being compared. The conversion is done by using the stringFO30 or numberFO30 function as appropriate. If the data-type attribute has any other effective value, then this value must be a EQName denoting an expanded QName with a non-absent namespace, and the effect of the attribute is implementation-defined.

[ERR XTTE1020] If any sort key value, after atomization and any type conversion required by the data-type attribute, is a sequence containing more than one item, then the effect depends on whether the xsl:sort element is processed with XSLT 1.0 behavior. With XSLT 1.0 behavior, the effective sort key value is the first item in the sequence. In other cases, this is a type error.

The set of sort key values (after any conversion) is first divided into two categories: empty values, and ordinary values. The empty sort key values represent those items where the sort key value is an empty sequence. These values are considered for sorting purposes to be equal to each other, but less than any other value. The remaining values are classified as ordinary values.

[ERR XTDE1030] It is a dynamic error if, for any sort key component, the set of sort key values evaluated for all the items in the initial sequence, after any type conversion requested, contains a pair of ordinary values for which the result of the XPath lt operator is an error.

Note:

The above error condition may occur if the values to be sorted are of a type that does not support ordering (for example, xs:QName) or if the sequence is heterogeneous (for example, if it contains both strings and numbers). The error can generally be prevented by invoking a cast or constructor function within the sort key component.

The error condition is subject to the usual caveat that a processor is not required to evaluate any expression solely in order to determine whether it raises an error. For example, if there are several sort key components, then a processor is not required to evaluate or compare minor sort key values unless the corresponding major sort key values are equal.

In general, comparison of two ordinary values is performed according to the rules of the XPath lt operator. To ensure a total ordering, the same implementation of the lt operator must be used for all the comparisons: the one that is chosen is the one appropriate to the most specific type to which all the values can be converted by subtype substitution and/or type promotion. For example, if the sequence contains both xs:decimal and xs:double values, then the values are compared using xs:double comparison, even when comparing two xs:decimal values. NaN values, for sorting purposes, are considered to be equal to each other, and less than any other numeric value. Special rules also apply to the xs:string and xs:anyURI types, and types derived by restriction therefrom, as described in the next section.

13.1.3 Sorting Using Collations

The rules given in this section apply when comparing values whose type is xs:string or a type derived by restriction from xs:string, or whose type is xs:anyURI or a type derived by restriction from xs:anyURI.

[Definition: Facilities in XSLT 3.0 and XPath 3.0 that require strings to be ordered rely on the concept of a named collation. A collation is a set of rules that determine whether two strings are equal, and if not, which of them is to be sorted before the other.] A collation is identified by a URI, but the manner in which this URI is associated with an actual rule or algorithm is largely implementation-defined.

For more information about collations, see Section 5.3 Comparison of strings FO30 in [Functions and Operators]. Some specifications, for example [UNICODE TR10], use the term "collation" to describe rules that can be tailored or parameterized for various purposes. In this specification, a collation URI refers to a collation in which all such parameters have already been fixed. Therefore, if a collation URI is specified, other attributes such as case-order and lang are ignored.

Every implementation must recognize the collation URI that must http://www.w3.org/2005/xpath-functions/collation/codepoint, which provides the ability to compare strings based on the Unicode codepoint values of the characters in the string.

Furthermore, every imlementation must recognize collation URIs representing tailorings of the Unicode Collation Algorithm (UCA), as described in 13.4 The Unicode Collation Algorithm. Although this form of collation URI must be recognized, implementations are not required to support every possible tailoring.

If the xsl:sort element has a collation attribute, then the strings are compared according to the rules for the named collation: that is, they are compared using the XPath function call compare($a, $b, $collation).

If the effective value of the collation attribute of xsl:sort is a relative URI, then it is resolved against the base URI of the xsl:sort element.

[ERR XTDE1035] It is a dynamic error if the collation attribute of xsl:sort (after resolving against the base URI) is not a URI that is recognized by the implementation as referring to a collation.

Note:

It is entirely for the implementation to determine whether it recognizes a particular collation URI. For example, if the implementation allows collation URIs to contain parameters in the query part of the URI, it is the implementation that determines whether a URI containing an unknown or invalid parameter is or is not a recognized collation URI. The fact that this situation is described as an error thus does not prevent an implementation applying a fallback collation if it chooses to do so.

The lang and case-order attributes are ignored if a collation attribute is present. But in the absence of a collation attribute, these attributes provide input to an implementation-defined algorithm to locate a suitable collation:

  • The lang attribute indicates that a collation suitable for a particular natural language should be used. The effective value of the attribute must be a value that would be valid for the xml:lang attribute (see [XML 1.0]).

  • The case-order attribute indicates whether the desired collation should sort upper-case letters before lower-case or vice versa. The effective value of the attribute must be either lower-first (indicating that lower-case letters precede upper-case letters in the collating sequence) or upper-first (indicating that upper-case letters precede lower-case).

    When lower-first is requested, the returned collation should have the property that when two strings differ only in the case of one or more characters, then a string in which the first differing character is lower-case should precede a string in which the corresponding character is title-case, which should in turn precede a string in which the corresponding character is upper-case. When upper-first is requested, the returned collation should have the property that when two strings differ only in the case of one or more characters, then a string in which the first differing character is upper-case should precede a string in which the corresponding character is title-case, which should in turn precede a string in which the corresponding character is lower-case.

    So, for example, if lang="en", then A a B b are sorted with case-order="upper-first" and a A b B are sorted with case-order="lower-first".

    As a further example, if lower-first is requested, then a sorted sequence might be "MacAndrew, macintosh, macIntosh, Macintosh, MacIntosh, macintoshes, Macintoshes, McIntosh". If upper-first is requested, the same sequence would sort as "MacAndrew, MacIntosh, Macintosh, macIntosh, macintosh, MacIntoshes, macintoshes, McIntosh".

If none of the collation, lang, or case-order attributes is present, the collation is chosen in an implementation-defined way. It is not required that the default collation for sorting should be the same as the default collation used when evaluating XPath expressions, as described in 5.4.1 Initializing the Static Context and 3.8.1 The default-collation Attribute.

Note:

It is usually appropriate, when sorting, to use a strong collation, that is, one that takes account of secondary differences (accents) and tertiary differences (case) between strings that are otherwise equal. A weak collation, which ignores such differences, may be more suitable when comparing strings for equality.

Useful background information on international sorting is provided in [UNICODE TR10]. The case-order attribute may be interpreted as described in section 6.6 of [UNICODE TR10].

13.2 Creating a Sorted Sequence

<!-- Category: instruction -->
<xsl:perform-sort
  select? = expression >
  <!-- Content: (xsl:sort+, sequence-constructor) -->
</xsl:perform-sort>

The xsl:perform-sort instruction is used to return a sorted sequence.

The initial sequence is obtained either by evaluating the select attribute or by evaluating the contained sequence constructor (but not both). If there is no select attribute and no sequence constructor then the initial sequence (and therefore, the sorted sequence) is an empty sequence.

[ERR XTSE1040] It is a static error if an xsl:perform-sort instruction with a select attribute has any content other than xsl:sort and xsl:fallback instructions.

The result of the xsl:perform-sort instruction is the result of sorting its initial sequence using its contained sort key specification.

Example: Sorting a Sequence of Atomic Values

The following stylesheet function sorts a sequence of atomic values using the value itself as the sort key.

<xsl:function name="local:sort" 
          as="xs:anyAtomicType*">
  <xsl:param name="in" as="xs:anyAtomicType*"/>
  <xsl:perform-sort select="$in">
    <xsl:sort select="."/>
  </xsl:perform-sort>
</xsl:function>

 

Example: Writing a Function to Perform a Sort

The following example defines a function that sorts books by price, and uses this function to output the five books that have the lowest prices:

<xsl:function name="bib:books-by-price" 
          as="schema-element(bib:book)*">
  <xsl:param name="in" as="schema-element(bib:book)*"/>
  <xsl:perform-sort select="$in">
    <xsl:sort select="xs:decimal(bib:price)"/>
  </xsl:perform-sort>
</xsl:function>
   ...
   <xsl:copy-of select="bib:books-by-price(//bib:book)
                             [position() = 1 to 5]"/>

 

13.3 Processing a Sequence in Sorted Order

When used within xsl:for-each or xsl:apply-templates, a sort key specification indicates that the sequence of items selected by that instruction is to be processed in sorted order, not in the order of the supplied sequence.

Example: Processing Elements in Sorted Order

For example, suppose an employee database has the form

<employees>
  <employee>
    <name>
      <given>James</given>
      <family>Clark</family>
    </name>
    ...
  </employee>
</employees>

Then a list of employees sorted by name could be generated using:

<xsl:template match="employees">
  <ul>
    <xsl:apply-templates select="employee">
      <xsl:sort select="name/family"/>
      <xsl:sort select="name/given"/>
    </xsl:apply-templates>
  </ul>
</xsl:template>

<xsl:template match="employee">
  <li>
    <xsl:value-of select="name/given"/>
    <xsl:text> </xsl:text>
    <xsl:value-of select="name/family"/>
  </li>
</xsl:template>

When used within xsl:for-each-group, a sort key specification indicates the order in which the groups are to be processed. For the effect of xsl:for-each-group, see 14 Grouping.

13.4 The Unicode Collation Algorithm

XSLT 3.0 defines a family of collation URIs representing tailorings of the Unicode Collation Algorithm (UCA) as defined in [UNICODE TR10]. The parameters used for tailoring the UCA are based on the parameters defined in the Locale Data Markup Language (LDML), defined in [UNICODE TR35].

This family of URIs use the scheme and path http://www.w3.org/2013/collation/UCA followed by an optional query part. The query part, if present, consists of a question mark followed by a sequence of zero or more semicolon-separated parameters. Each parameter is a keyword-value pair, the keyword and value being separated by an equals sign.

All implementations must recognize URIs in this family. This applies to all places where collations are used, including (for example) the xsl:sort, xsl:key, xsl:for-each-group, and xsl:merge-key elements, the [xsl:]default-collation attribute, and the collation argument of core functions. If the fallback parameter is present with the value no, then the implementation must either use a collation that conforms with the rules in the Unicode specifications for the requested tailoring, or fail with a static or dynamic error indicating that it does not provide the collation (the error code should be the same as if the collation URI were not recognized). If the fallback parameter is omitted or takes the value yes, and if the collation URI is well-formed according to the rules in this section, then the implementation must accept the collation URI, and should use the available collation that most closely reflects the user's intentions. For example, if the collation URI requested is http://www.w3.org/2013/collation/UCA?lang=se;fallback=yes and the implementation does not include a fully conformant version of the UCA tailored for Swedish, then it may choose to use a Swedish collation that is known to differ from the UCA definition, or one whose conformance has not been established. It might even, as a last resort, fall back to using codepoint collation.

If two query parameters use the same keyword then the last one wins. If a query parameter uses a keyword or value which is not defined in this specification then the meaning is implementation-defined. If the implementation recognizes the meaning of the keyword and value then it should interpret it accordingly; if it does not recognize the keyword or value then if the fallback parameter is present with the value no it should reject the collation as unsupported, otherwise it should ignore the unrecognized parameter.

The following query parameters are defined. If any parameter is absent, the default is implementation-defined except where otherwise stated. The meaning given for each parameter is non-normative; the normative specification is found in [UNICODE TR35].

Keyword Values Meaning
fallback yes | no (default yes) Determines whether the processor uses a fallback collation if a conformant collation is not available.
lang language code, as defined for the lang attribute of xsl:sort The language whose collation conventions are to be used.
version string The version number of the UCA to be used.
strength primary | secondary | tertiary | quaternary | identical, or 1|2|3|4|5 as synonyms The collation strength as defined in UCA. Primary strength takes only the base form of the characater into account (so A=a=Â=â); secondary strength ignores case but considers accents and diacritics as significant (so A=a and Â=â but â!=a); tertiary considers case as significant (A!=a!=Â!=â); quaternary considers spaces and punctuation that would otherwise be ignored (for example data-base=database).
alternate non-ignorable | shifted | blanked Controls the effect of characters such as spaces and hyphens.
backwards yes | no The value backwards=yes indicates that the last accent in the search term is the most significant.
normalization yes | no Indicates whether search terms are converted to normalization form D.
caseLevel yes | no When used with primary strength, setting caseLevel=yes has the effect of ignoring accents while taking account of case.
caseFirst upper | lower Indicates whether upper-case precedes lower-case or vice versa.
hiraganaQuaternary yes | no Controls special treatment of Hiragana codepoints when strength is quaternary or greater.
numeric yes | no When numeric=yes is specified, a sequence of consecutive digits is interpreted as a number, for example chap2 sorts before chap12.
reorder a comma-separated sequence of reorder codes, where a reorder code is one of space, punct, symbol, currency, digit, or a four-letter script code defined in [ISO 15924 Register], the register of scripts maintained by the Unicode Consortium in its capacity as registration authority for [ISO 15924]. Determines the relative ordering of text in different scripts; for example the value digit,Grek,Latn indicates that digits precede Greek letters, which precede Latin letters.

Note:

This list excludes parameters that are inconvenient to express in a URI, or that are applicable only to substring matching.

14 Grouping

The facilities described in this section are designed to allow items in a sequence to be grouped based on common values; for example it allows grouping of elements having the same value for a particular attribute, or elements with the same name, or elements with common values for any other expression. Since grouping identifies items with duplicate values, the same facilities also allow selection of the distinct values in a sequence of items, that is, the elimination of duplicates.

Note:

Simple elimination of duplicates can also be achieved using the function distinct-valuesFO30 in the core function library: see [Functions and Operators].

In addition these facilities allow grouping based on sequential position, for example selecting groups of adjacent para elements. The facilities also provide an easy way to do fixed-size grouping, for example identifying groups of three adjacent nodes, which is useful when arranging data in multiple columns.

For each group of items identified, it is possible to evaluate a sequence constructor for the group. Grouping is nestable to multiple levels so that groups of distinct items can be identified, then from among the distinct groups selected, further sub-grouping of distinct items in the current group can be done.

It is also possible for one item to participate in more than one group.

14.1 The xsl:for-each-group Element

<!-- Category: instruction -->
<xsl:for-each-group
  select = expression
  group-by? = expression
  group-adjacent? = expression
  group-starting-with? = pattern
  group-ending-with? = pattern
  bind-group? = eqname
  bind-grouping-key? = eqname
  composite? = "yes" | "no"
  collation? = { uri } >
  <!-- Content: (xsl:sort*, sequence-constructor) -->
</xsl:for-each-group>

This element is an instruction that may be used anywhere within a sequence constructor.

[Definition: The xsl:for-each-group instruction allocates the items in an input sequence into groups of items (that is, it establishes a collection of sequences) based either on common values of a grouping key, or on a pattern that the initial or final item in a group must match.] The sequence constructor that forms the content of the xsl:for-each-group instruction is evaluated once for each of these groups.

[Definition: The sequence of items to be grouped, which is referred to as the population, is determined by evaluating the XPath expression contained in the select attribute.]

[Definition: The population is treated as a sequence; the order of items in this sequence is referred to as population order ].

A group is never empty. If the population is empty, the number of groups will be zero.

The assignment of items to groups depends on the group-by, group-adjacent, group-starting-with, and group-ending-with attributes.

[ERR XTSE1080] These four attributes are mutually exclusive: it is a static error if none of these four attributes is present or if more than one of them is present.

[ERR XTSE1090] It is a static error to specify the collation attribute or the composite attribute if neither the group-by attribute nor group-adjacent attribute is specified.

[Definition: If either of the group-by or group-adjacent attributes is present, then for each item in the population a set of grouping keys is calculated, as follows: the expression contained in the group-by or group-adjacent attribute is evaluated; the result is atomized; and any xs:untypedAtomic values are cast to xs:string. If composite="yes" is specified, there is a single grouping key whose value is the resulting sequence; otherwise, there is a set of grouping keys, consisting of the distinct atomic values present in the result sequence. ]

When calculating grouping keys for an item in the population, the expression contained in the group-by or group-adjacent attribute is evaluated with that item as the context item, with its position in population order as the context position, and with the size of the population as the context size.

If the group-by attribute is present, and if the composite attribute is omitted or takes the value no, then an item in the population may have multiple grouping keys: that is, the group-by expression evaluates to a sequence, and each item in the sequence is treated as a separate grouping key. The item is included in as many groups as there are distinct grouping keys (which may be zero).

f the group-adjacent attribute is used, and if the composite attribute is omitted or takes the value no, then each item in the population must have exactly one grouping key value.

[ERR XTTE1100] It is a type error if the result of evaluating the group-adjacent expression is an empty sequence or a sequence containing more than one item, unless composite="yes" is specified.

Grouping keys are compared using the rules for the deep-equalFO30 function. This means that values of type xs:untypedAtomic will be cast to xs:string before the comparison, and that items that are not comparable using the eq operator are considered to be not equal, that is, they are allocated to different groups. It also means that the value NaN is considered equal to itself. If the values are strings, or untyped atomic values, then if there is a collation attribute the values are compared using the collation specified as the effective value of the collation attribute, resolved if relative against the base URI of the xsl:for-each-group element. If there is no collation attribute then the default collation is used.

[ERR XTDE1110] It is a dynamic error if the collation URI specified to xsl:for-each-group (after resolving against the base URI) is a collation that is not recognized by the implementation. (For notes, [see ERR XTDE1035].)

For more information on collations, see 13.1.3 Sorting Using Collations.

The way in which an xsl:for-each-group element is evaluated depends on which of the four group-defining attributes is present:

  • If the group-by attribute is present, the items in the population are examined, in population order. For each item J, the expression in the group-by attribute is evaluated to produce a sequence of zero or more grouping key values. If composite="yes" is specified, there will be a single grouping key, which will in general be a sequence of zero or more atomic values; otherwise, there will be zero or more grouping keys, each of which will be a single atomic value. For each one of these grouping keys, if there is already a group created to hold items having that grouping key value, J is appended to that group; otherwise a new group is created for items with that grouping key value, and J becomes its first member.

    An item in the population may thus be appended to zero, one, or many groups. An item will never be appended more than once to the same group; if two or more grouping keys for the same item are equal, then the duplicates are ignored. An item here means the item at a particular position within the population—if the population contains the same node at several different positions in the sequence then a group may indeed contain duplicate nodes.

    The number of groups will be the same as the number of distinct grouping key values present in the population.

    If the population contains values of different numeric types that differ from each other by small amounts, then the eq operator is not transitive, because of rounding effects occurring during type promotion. The effect of this is described in 14.5 Non-Transitivity.

  • If the group-adjacent attribute is present, the items in the population are examined, in population order. If an item has the same value for the grouping key as its preceding item within the population (in population order), then it is appended to the same group as its preceding item; otherwise a new group is created and the item becomes its first member.

  • If the group-starting-with attribute is present, then its value must be a pattern.

    The items in the population are examined in population order. If an item matches the pattern, or is the first item in the population, then a new group is created and the item becomes its first member. Otherwise, the item is appended to the same group as its preceding item within the population.

  • If the group-ending-with attribute is present, then its value must be a pattern.

    The items in the population are examined in population order. If an item is the first item in the population, or if the previous item in the population matches the pattern, then a new group is created and the item becomes its first member. Otherwise, the item is appended to the same group as its preceding item within the population.

In all cases the order of items within each group is predictable, and reflects the original population order, in that the items are processed in population order and each item is appended at the end of zero or more groups.

Note:

As always, a different algorithm may be used if it achieves the same effect.

[Definition: For each group, the item within the group that is first in population order is known as the initial item of the group.]

The sequence constructor contained in the xsl:for-each-group element is evaluated once for each of the groups, in processing order. The sequences that result are concatenated, in processing order, to form the result of the xsl:for-each-group element. Within the sequence constructor, the context item is the initial item of the relevant group, the context position is the position of this group in the processing order of the groups, and the context size is the number of groups This has the effect that within the sequence constructor, a call on position() takes successive values 1, 2, ... last().

14.2 Accessing Information about the Current Group Value

Two pieces of information are available during the processing of each group (that is, while evaluating the sequence constructor contained in the xsl:for-each-group instruction, and also while evaluating the sort key of a group as expressed by the select attribute or sequence constructor of an xsl:sort child of the xsl:for-each-group element):

  • [Definition: The current group value is the group itself, as a sequence of items].

  • [Definition: The current grouping key value is a single atomic value, or in the case of a composite key, a sequence of atomic values, containing the grouping key of the items in the current group value.]

There are two ways of getting this information. The preferred way in XSLT 3.0 is to bind variables using the bind-group and bind-grouping-key attributes of the xsl:for-each-group instruction.

If the bind-group attribute is present, then its value must be an EQName, and this causes a local variable binding for this name to be visible within the sequence constructor forming the body of the xsl:for-each-group instruction, and also within any xsl:sort element child of the xsl:for-each-group element. The type of the variable is item()* (any sequence of items), and its value is the content of the current group value.

If the bind-grouping-key attribute is present, then its value must be a EQName, and this causes a local variable binding for this name to be present within the sequence constructor forming the body of the xsl:for-each-group instruction and also within any xsl:sort element child of the xsl:for-each-group element. The type of the variable is anyAtomicType* (any sequence of atomic values), and its value is the current grouping key value, that is the grouping key of the group being processed.

If the variable names bound in the bind-group or bind-grouping-key attributes are used in the select attribute or the sequence constructor within an xsl:sort child of the xsl:for-each-group instruction, then they act as references to the group whose sort key is being computed, or the grouping key of that group, respectively.

Except as noted below, the variable bindings established by the bind-group and bind-grouping-key attributes, when present, are visible within all descendant elements of the xsl:for-each-group instruction on which they are declared, other than elements where the variable binding is shadowed by another variable binding. For more information see 9.9 Scope of Variables.

[ERR XTSE3220] It is a static error if a variable bound in the bind-group or bind-grouping-key attribute of an xsl:for-each-group instruction is referenced within an expression in the lang, order, collation, stable, case-order, or data-type attributes of an xsl:sort child of that xsl:for-each-group instruction.

[ERR XTSE3230] It is a static error if the bind-grouping-key attribute is present on an xsl:for-each-group instruction unless either the group-by or group-adjacent attribute is present.

For backwards compatibility, XSLT 3.0 also allows information about the current group value and the current grouping key value to be held in the dynamic context, and obtained therefrom using the current-group and current-grouping-key functions respectively. The difference between using bound variables and using these functions is that the variables have static scope (they can only be used lexically within the xsl:for-each-group element), whereas the functions have dynamic scope (they are available in called templates — though not in called functions — as well as within the lexical body of xsl:for-each-group). The fact that the functions have dynamic scope makes certain optimizations difficult, and in particular it makes it impossible to satisfy the rules for streamability. When streamed processing is required, therefore, it is necessary to bind variables to the group and grouping key rather than using the current-group and current-grouping-key functions.

Note:

The terms current group value and current grouping key value refer to the group and grouping key being processed, regardless whether these are bound to variables or held in the dynamic context. The terms current group and current grouping key refer to the values held in the dynamic context, which are set to hold the current group value and current grouping key value only when these values have not been bound to variables.

An added benefit of using the bind-group and bind-grouping-key variables is apparent when xsl:for-each-group elements are nested: the grouping variables for the outer instruction remain in scope when processing the inner instruction.

If the bind-group attribute is present on the xsl:for-each-group instruction, then the current group (the value accessed by the current-group function) is set to absent during the processing of the instruction, which has the effect that any call on current-group results in a dynamic error.

If the bind-grouping-key attribute is present on the xsl:for-each-group instruction, or if neither the group-by nor group-adjacent attribute is present, then the current grouping key (the value accessed by the current-grouping-key function) is set to absent during the processing of the instruction, which has the effect that any call on current-grouping-key results in a dynamic error.

14.2.1 fn:current-group

Summary

Returns the group currently being processed by an xsl:for-each-group instruction.

Signature

current-group() as item()*
Properties

This function is deterministicFO30, context-dependentFO30, and focus-independentFO30.

Rules

[Definition: The evaluation context for XPath expressions includes a component called the current group, which is a sequence.]

The current group is bound during evaluation of the xsl:for-each-group instruction. If no xsl:for-each-group instruction is being evaluated, the current group will be absent: that is, any reference to it will cause a dynamic error.

The scope of the current group is dynamic: its value is retained through calls on named templates, template rules, and attribute sets. It is cleared (becomes absent) during non-contextual function calls, and during the evaluation of global variables and stylesheet parameters. It is also cleared during calls on xsl:for-each-group that use a bind-group attribute.

The function current-group returns the sequence of items making up the current group.

Error Conditions

[ERR XTSE1060] It is a static error if the current-group function is used within a pattern.

[ERR XTDE1061] It is a dynamic error if the current-group function is used when the current group is absent , or when it is invoked in the course of evaluating a pattern. The error may be reported statically if it can be detected statically.

Notes

The function is classified as focus-dependentFO30, which means that it cannot be used with higher-order functions. Specifically, current-group#0 will not be recognized as a function literal.

14.2.2 fn:current-grouping-key

Summary

Returns the grouping key of the group currently being processed using the xsl:for-each-group instruction.

Signature

current-grouping-key() as xs:anyAtomicType*
Properties

This function is deterministicFO30, context-dependentFO30, and focus-independentFO30.

Rules

[Definition: The evaluation context for XPath expressions includes a component called the current grouping key, which is a sequence of atomic values. The current grouping key is the grouping key shared in common by all the items within the current group.]

The current grouping key is bound during evaluation of the xsl:for-each-group instruction. If no xsl:for-each-group instruction is being evaluated, the current grouping key will be absent, which means that any reference to it causes a dynamic error.

The scope of the current grouping key is dynamic: its value is retained through calls on named templates, template rules, and attribute sets. It is cleared (becomes absent) during non-contextual function calls, and during the evaluation of global variables and stylesheet parameters. It is also cleared during calls on xsl:for-each-group that use a group-starting-with or group-ending-with or bind-grouping-key attribute.

While an xsl:for-each-group instruction with a group-by or group-adjacent attribute is being evaluated, the current grouping key will be a single atomic value if composite="no" is specified (explicitly or implicitly), or a sequence of atomic values if composite="yes" is specified.

At other times, the current grouping key will be absent.

The function current-grouping-key returns the current grouping key.

The grouping keys of all items in a group are not necessarily identical. For example, one might be an xs:float while another is a numerically equal xs:decimal. The current-grouping-key function returns the grouping key of the initial item in the group, after atomization and casting of xs:untypedAtomic values to xs:string.

The function takes no arguments.

Error Conditions

[ERR XTSE1070] It is a static error if the current-grouping-key function is used within a pattern.

[ERR XTDE1071] It is a dynamic error if the current-grouping-key function is used when the current grouping key is absent, or when it is invoked in the course of evaluating a pattern.. The error may be reported statically if it can be detected statically.

Notes

The function is classified as focus-dependentFO30, which means that it cannot be used with higher-order functions. Specifically, current-grouping-key#0 will not be recognized as a function literal.

14.3 Ordering among Groups

[Definition: There is a total ordering among groups referred to as the order of first appearance. A group G is defined to precede a group H in order of first appearance if the initial item of G precedes the initial item of H in population order. If two groups G and H have the same initial item (because the item is in both groups) then G precedes H if the grouping key of G precedes the grouping key of H in the sequence that results from evaluating the group-by expression of this initial item.]

[Definition: There is another total ordering among groups referred to as processing order. If group R precedes group S in processing order, then in the result sequence returned by the xsl:for-each-group instruction the items generated by processing group R will precede the items generated by processing group S.]

If there are no xsl:sort elements immediately within the xsl:for-each-group element, the processing order of the groups is the order of first appearance.

Otherwise, the xsl:sort elements immediately within the xsl:for-each-group element define the processing order of the groups (see 13 Sorting). They do not affect the order of items within each group. Multiple sort key components are allowed, and are evaluated in major-to-minor order. If two groups have the same values for all their sort key components, they are processed in order of first appearance if the sort key specification is stable, otherwise in an implementation-dependent order.

The select expression of an xsl:sort element is evaluated once for each group. During this evaluation, the context item is the initial item of the group, the context position is the position of this item within the set of initial items (that is, one item for each group in the population) in population order, the context size is the number of groups, the current group value is the group whose sort key value is being determined, and the current grouping key value is the grouping key for that group. If the xsl:for-each-group instruction uses the group-starting-with or group-ending-with attributes, then the current grouping key value is the empty sequence.

Example: Sorting Groups

For example, this means that if the grouping key is @category, you can sort the groups in order of their grouping key by writing <xsl:sort select="current-grouping-key()"/>; or you can sort the groups in order of size by writing <xsl:sort select="count(current-group())"/>

14.4 Examples of Grouping

These examples all use the bind-group and bind-grouping-key attributes introduced in XSLT 3.0. For equivalent examples using the current-group and current-grouping-key functions, see the XSLT 2.0 specification.

Example: Grouping Nodes based on Common Values

The following example groups a list of nodes based on common values. The resulting groups are numbered but unsorted, and a total is calculated for each group.

Source XML document:

<cities>
  <city name="Milano"  country="Italia"      pop="5"/>
  <city name="Paris"   country="France"      pop="7"/>
  <city name="München" country="Deutschland" pop="4"/>
  <city name="Lyon"    country="France"      pop="2"/>
  <city name="Venezia" country="Italia"      pop="1"/>
</cities>

More specifically, the aim is to produce a four-column table, containing one row for each distinct country. The four columns are to contain first, a sequence number giving the number of the row; second, the name of the country, third, a comma-separated alphabetical list of the city names within that country, and fourth, the sum of the pop attribute for the cities in that country.

Desired output:

<table>
  <tr>
    <th>Position</th>
    <th>Country</th>
    <th>List of Cities</th>
    <th>Population</th>
  </tr>
  <tr>
    <td>1</td>
    <td>Italia</td>
    <td>Milano, Venezia</td>
    <td>6</td>
  </tr>
  <tr>
    <td>2</td>
    <td>France</td>
    <td>Lyon, Paris</td>
    <td>9</td>
  </tr>  
  <tr>
    <td>3</td>
    <td>Deutschland</td>
    <td>München</td>
    <td>4</td>
  </tr>  
</table>

Solution:

<table xsl:version="3.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <tr>
    <th>Position</th>
    <th>Country</th>
    <th>City List</th>
    <th>Population</th>
  </tr>
  <xsl:for-each-group select="cities/city" group-by="@country" 
       bind-group="cities" bind-grouping-key="country">
    <tr>
      <td><xsl:value-of select="position()"/></td>
      <td><xsl:value-of select="$country"/></td>
      <td>
        <xsl:value-of select="$cities/@name" separator=", "/>
      </td>
      <td><xsl:value-of select="sum($cities/@pop)"/></td>
    </tr>
  </xsl:for-each-group>
</table>

 

Example: A Composite Grouping Key

Sometimes it is necessary to use a composite grouping key: for example, suppose the source document is similar to the one used in the previous examples, but allows multiple entries for the same country and city, such as:

<cities>
  <city name="Milano"  country="Italia"  year="1950"   pop="5.23"/>
  <city name="Milano"  country="Italia"  year="1960"   pop="5.29"/>  
  <city name="Padova"  country="Italia"  year="1950"   pop="0.69"/>
  <city name="Padova"  country="Italia"  year="1960"   pop="0.93"/>    
  <city name="Paris"   country="France"  year="1951"   pop="7.2"/>
  <city name="Paris"   country="France"  year="1961"   pop="7.6"/>
</cities>

Now suppose we want to list the average value of @pop for each (country, name) combination. One way to handle this is to concatenate the parts of the key, for example <xsl:for-each-group select="concat(@country, '/', @name)">. A second solution is to nest one xsl:for-each-group element directly inside another. XSLT 3.0 introduces a third option, which is to define the grouping key as composite:

<xsl:for-each-group select="cities/city" 
                    group-by="@name, @country" 
                    composite="yes"
                    bind-group="group" 
                    bind-grouping-key="key">
  <p><xsl:value-of select="$key[1] || ', ' || $key[2] || ': ' || 
                           avg($group/@pop)"/></p>
                           </xsl:for-each-group>

Note:

The string concatenation operator || is new in XPath 3.0.

 

Example: Identifying a Group by its Initial Element

The next example identifies a group not by the presence of a common value, but rather by adjacency in document order. A group consists of an h2 element, followed by all the p elements up to the next h2 element.

Source XML document:

<body>
  <h2>Introduction</h2>
  <p>XSLT is used to write stylesheets.</p>
  <p>XQuery is used to query XML databases.</p>
  <h2>What is a stylesheet?</h2>
  <p>A stylesheet is an XML document used to define a transformation.</p>
  <p>Stylesheets may be written in XSLT.</p>
  <p>XSLT 2.0 introduces new grouping constructs.</p>
</body>

Desired output:

<chapter>
  <section title="Introduction">
    <para>XSLT is used to write stylesheets.</para>
    <para>XQuery is used to query XML databases.</para>
  </section> 
  <section title="What is a stylesheet?">
    <para>A stylesheet is used to define a transformation.</para>
    <para>Stylesheets may be written in XSLT.</para>
    <para>XSLT 2.0 introduces new grouping constructs.</para>
  </section>
</chapter>

Solution:

<xsl:template match="body">
  <chapter>
        <xsl:for-each-group select="*" group-starting-with="h2"
                       bind-group="h2-et-seq"   >
          <section title="{self::h2}">
            <xsl:for-each select="$h2-et-seq[self::p]">
              <para><xsl:value-of select="."/></para>
            </xsl:for-each> 
          </section>
        </xsl:for-each-group>
  </chapter>
</xsl:template>

The use of title="{self::h2}" rather than title="{.}" is to handle the case where the first element is not an h2 element.

 

Example: Identifying a Group by its Final Element

The next example illustrates how a group of related elements can be identified by the last element in the group, rather than the first. Here the absence of the attribute continued="yes" indicates the end of the group.

Source XML document:

<doc>
  <page continued="yes">Some text</page>
  <page continued="yes">More text</page>    
  <page>Yet more text</page>
  <page continued="yes">Some words</page>
  <page continued="yes">More words</page>    
  <page>Yet more words</page>        
</doc>

Desired output:

<doc>
  <pageset>
    <page>Some text</page>
    <page>More text</page>    
    <page>Yet more text</page>
  </pageset>
  <pageset>
    <page>Some words</page>
    <page>More words</page>    
    <page>Yet more words</page>
  </pageset>
</doc>

Solution:

<xsl:template match="doc">
<doc>
  <xsl:for-each-group select="*" 
                      group-ending-with="page[not(@continued='yes')]"
                      bind-group="pageset">
    <pageset>
      <xsl:for-each select="$pageset">
        <page><xsl:value-of select="."/></page>
      </xsl:for-each> 
    </pageset>
  </xsl:for-each-group>
</doc>
</xsl:template>

 

Example: Adding an Element to Several Groups

The next example shows how an item can be added to multiple groups. Book titles will be added to one group for each indexing term marked up within the title.

Source XML document:

<titles>
    <title>A Beginner's Guide to <ix>Java</ix></title>
    <title>Learning <ix>XML</ix></title>
    <title>Using <ix>XML</ix> with <ix>Java</ix></title>
</titles>

Desired output:

<h2>Java</h2>
    <p>A Beginner's Guide to Java</p>
    <p>Using XML with Java</p>
<h2>XML</h2>
    <p>Learning XML</p>
    <p>Using XML with Java</p>

Solution:

<xsl:template match="titles">
    <xsl:for-each-group select="title" group-by="ix"
                        bind-group="group" bind-grouping-key="key">
      <h2><xsl:value-of select="$key"/></h2>
      <xsl:for-each select="$group">
        <p><xsl:value-of select="."/></p>
      </xsl:for-each>
    </xsl:for-each-group>
</xsl:template>

 

Example: Grouping Alternating Sequences of Elements

In this example, the membership of a node within a group is based both on adjacency of the nodes in document order, and on common values. In this case, the grouping key is a boolean condition, true or false, so the effect is that a grouping establishes a maximal sequence of nodes for which the condition is true, followed by a maximal sequence for which it is false, and so on.

Source XML document:

<p>Do <em>not</em>:
    <ul>
    <li>talk,</li>
    <li>eat, or</li>
    <li>use your mobile telephone</li>
    </ul>
    while you are in the cinema.</p>

Desired output:

<p>Do <em>not</em>:</p>
    <ul>
    <li>talk,</li>
    <li>eat, or</li>
    <li>use your mobile telephone</li>
    </ul>
    <p>while you are in the cinema.</p>

Solution:

This requires creating a p element around the maximal sequence of sibling nodes that does not include a ul or ol element.

This can be done by using group-adjacent, with a grouping key that is true if the element is a ul or ol element, and false otherwise:

<xsl:template match="p">
    <xsl:for-each-group select="node()" 
            group-adjacent="self::ul or self::ol"
            bind-group="group" bind-grouping-key="is-list">
        <xsl:choose>
            <xsl:when test="$is-list">
                <xsl:copy-of select="$group"/>  
            </xsl:when>
            <xsl:otherwise>
                <p>
                    <xsl:copy-of select="$group"/>
                </p>
            </xsl:otherwise>  
        </xsl:choose>
    </xsl:for-each-group>
</xsl:template>

14.5 Non-Transitivity

If the population contains values of different numeric types that differ from each other by small amounts, then the eq operator is not transitive, because of rounding effects occurring during type promotion. It is thus possible to have three values A, B, and C among the grouping keys of the population such that A eq B, B eq C, but A ne C.

For example, this arises when computing

      <xsl:for-each-group group-by="." select="
             xs:float('1.0'),
             xs:decimal('1.0000000000100000000001'),
             xs:double('1.00000000001')">

because the values of type xs:float and xs:double both compare equal to the value of type xs:decimal but not equal to each other.

In this situation the results must be equivalent to the results obtained by the following algorithm:

  • For each item J in the population in population order, for each of the grouping keys K for that item in sequence, the processor identifies those existing groups G such that the grouping key of the initial item of G is equal to K.

  • If there is exactly one group G, then J is added to this group, unless J is already a member of this group.

  • If there is no group G, then a new group is created with J as its first item.

  • If there is more than one group G (which can only happen in exceptional circumstances involving non-transitivity), then one of these groups is selected in an implementation-dependent way, and J is added to this group, unless J is already a member of this group.

The effect of these rules is that (a) every item in a non-singleton group has a grouping key that is equal to that of at least one other item in that group, (b) for any two distinct groups, there is at least one pair of items (one from each group) whose grouping keys are not equal to each other.

15 Merging

The xsl:merge instruction allows a sorted sequence of items to be constructed by merging several input sequences, each of which is already sorted. Each input sequence must have a merge key (one or more atomic values that can be computed as a function of the items in the sequence); the input sequence must be pre-sorted on the value of its merge keys; and the merge keys for the different input sequences must be compatible in the sense that key values from an item in one sequence are always comparable with key values from an item in a different sequence.

For example, if two log files contain details of events sorted by date and time, then the xsl:merge instruction can be used to combine these into a single sequence that is also sorted by date and time.

The data written to the output sequence can be computed in an arbitrary way from the data in the input sequences, provided it follows the ordering of the input sequences.

The xsl:merge instruction can be used to merge several sequences of items that all have the same structure (more precisely, sequences whose merge keys are computed in the same way): for example, log files created by the same application running on different machines in a server farm. Alternatively, xsl:merge can be used to merge sequences that have different structure (sequences whose merge keys are computed in different ways), provided that the computed merge keys are compatible: an example might be two log files created by different applications, using different XML vocabularies, that both contain timestamped events but represent the timestamp in different ways. The xsl:merge-source element represents a set of input sequences that follow common rules, including the rules for computing the merge key. The xsl:merge operation may take any number of xsl:merge-source elements representing different rules for input sequences, and each xsl:merge-source element may describe any number (zero or more) of input sequences. The number of input sequences to the merging operation is thus fixed only at the time the xsl:merge instruction is evaluated, and may vary from one evaluation to another.

The following examples illustrate some of the possibilities. The detailed explanation of the constructs used follows later in this section.

Example: Merging All the Files in a Collection

This example takes as input a homogeneous collection of XML log files each of which contains a sorted sequence of event elements with a timestamp attribute validated as an instance of xs:dateTime. It merges the events from the input files into a single sorted output file.

<xsl:result-document href="merged-events.xml">
  <events>
    <xsl:merge bind-group="group">
      <xsl:merge-source for-each="collection('log-files')"
                        select="events/event">
        <xsl:merge-key select="@timestamp"/>
      </xsl:merge-source>
      <xsl:merge-action>
        <xsl:copy-of select="$group"/>
      </xsl:merge-action>
    </xsl:merge>
  </events>
</xsl:result-document>

The example assumes that there are several input files each of which has a structure similar to the following, in which the timestamp attribute has a typed value that is an instance of xs:dateTime:

<events>
   <event timestamp="2009-08-20T12:01:01Z">Transaction T1234 started</event>
   <event timestamp="2009-08-20T12:01:08Z">Transaction T1235 started</event>
   <event timestamp="2009-08-20T12:01:12Z">Transaction T1235 ended</event>
   <event timestamp="2009-08-20T12:01:15Z">Transaction T1234 ended</event>
</events>

The output file will have the same structure, and will contain copies of all the event elements from all of the input files, in sorted order. Note that multiple events with the same timestamp can occur either within a single file or across multiple files: the order of appearance of these events in the output file corresponds to the order of the log files within the collection (which might or might not be predictable, depending on the implementation).

 

Example: Merging Two Heterogeneous Files

This example takes as input two log files with different structure, producing a single merged output in which the entries have a common structure:

<xsl:result-document href="merged-events.xml">
  <events>
    <xsl:merge bind-group="grp">
      <xsl:merge-source select="doc('log-file-1.xml')/events/event">
        <xsl:merge-key select="@timestamp"/>
      </xsl:merge-source>
      <xsl:merge-source select="doc('log-files-2.xml')/log/day/record">
        <xsl:merge-key select="dateTime(../@date, time)"/>
      </xsl:merge-source>
      <xsl:merge-action>
        <xsl:apply-templates select="$grp" 
                             mode="standardize-log-entry"/>
      </xsl:merge-action>
    </xsl:merge>
  </events>
</xsl:result-document>

Here the first input file has a structure similar to that shown in the previous example, while the second input has a different structure, of the form:

<log>
  <day date="2009-08-20">
    <record>
      <time>12:01:09-05:00</time>
      <message>Temperature 15.4C</message>
    </record>
    <record>
      <time>12:03:00-05:00</time>
      <message>Temperature 18.2C</message>
    </record>
  </day>
</log>

The templates in mode standardize-log-entry convert the log entries to a common output format, for example:

<xsl:template match="event" mode="standardize-log-entry" 
                            as="schema-element(event)">
  <xsl:copy-of select="." validation="preserve"/>
</xsl:template>
  
<xsl:template match="record" mode="standardize-log-entry" 
                             as="schema-element(event)">
  <event timestamp="{dateTime(../@date, time)}" xsl:validation="strict">
    <xsl:value-of select="message"/>
  </event>
</xsl:template>

Note:

The xsl:merge instruction is designed to enable streaming of data, so that there is no need to allocate memory to hold the input sequences. However, there is no requirement that an implementation should actually use streaming to perform the processing.

15.1 Terminology for Merging

[Definition: A merge source definition is the definition of one kind of input to the merge operation. It selects zero or more merge input sequences, and it includes a merge key specification to define how the merge key values are computed for each such merge input sequence.] A merge source definition corresponds to an xsl:merge-source element in the stylesheet.

[Definition: A merge input sequence is an arbitrary sequenceDM30 of items which is already sorted according to the merge key specification for the corresponding merge source definition.]

[Definition: A merge key specification consists of one or more adjacent xsl:merge-key elements which together define how the merge input sequences selected by a merge source definition are sorted. Each xsl:merge-key element defines one merge key component.] For example, a merge key specification for a log file might specify two merge key components, date and time.

[Definition: A merge key component specifies one component of a merge key specification; it corresponds to a single xsl:merge-key element in the stylesheet.]

[Definition:  For each item in a merge input sequence, a value is computed for each merge key component within the merge key specification. The value computed for an item by using the Nth merge key component is referred to as the Nth merge key value of that item.]

[Definition:  The ordered collection of merge key values computed for one item in a merge input sequence (one for each merge key component within the merge key specification) is referred to as a composite merge key value.]

[Definition: A merge activation is a single evaluation of the sequence constructor contained within the xsl:merge-action element, which occurs once for each distinct composite merge key value.]

15.2 The xsl:merge Instruction

<!-- Category: instruction -->
<xsl:merge
  bind-group? = eqname
  bind-key? = eqname >
  <!-- Content: (xsl:merge-source+, xsl:merge-action, xsl:fallback*) -->
</xsl:merge>

The effect of the xsl:merge instruction is to produce a sorted result sequence from a number of input sequences.

The input sequences to the merge operation are defined by the xsl:merge-source child elements, as described in the next section.

The sequence constructor contained in the xsl:merge-action element is evaluated once for each distinct composite merge key value to form a partial result sequence. The result of the xsl:merge instruction is the concatenation of these partial result sequences. For example, the action might be to copy the items from all the input sequences to the result sequence without change; or it might be to select the items from one input sequence in preference to the others. In the general case, the items in the partial result sequence are produced by an arbitrary computation that has access to the items (from the various input sequences) that share the same value for the composite merge key.

The xsl:merge-source and xsl:merge-action elements are described in the following sections.

The bind-group attribute establishes the name of a variable which is available for reference within the xsl:merge-action element, and whose value is a sequence of items, from all input sources, that share a common composite merge key value.

The bind-key attribute establishes the name of a variable which is available for reference within the xsl:merge-action element, and whose value is the composite merge key value of these items.

Any xsl:fallback children of the xsl:merge instruction are ignored by an XSLT 3.0 processor, but are used by an XSLT 1.0 or XSLT 2.0 processor to perform fallback processing.

Note:

An xsl:merge instruction that has no input sequences returns an empty sequence. An xsl:merge instruction with a single input sequence performs processing that is very similar in concept to xsl:for-each-group with the group-adjacent attribute, except that it requires the input to be sorted on the grouping key.

15.3 Selecting the Sequences to be Merged

<xsl:merge-source
  for-each? = expression
  select = expression
  bind-source? = eqname
  streamable? = "yes" | "no"
  sort-before-merge? = "yes" | "no" >
  <!-- Content: xsl:merge-key+ -->
</xsl:merge-source>

Each xsl:merge-source element defines one or more merge input sequences.

In the absence of the for-each attribute, the xsl:merge-source element defines a single merge input sequence. This sequence is the result of evaluating the expression in the select attribute. This is evaluated using the dynamic context of the containing xsl:merge instruction.

When the for-each attribute is present, the xsl:merge-source element defines a collection of merge input sequences. The selection of items in these input sequences is a two-stage process: the for-each attribute of the xsl:merge-source element is an expression that selects a sequence of anchor items, and for each anchor item, the select attribute is evaluated to select the items that make up one merge input sequence. The for-each expression is evaluated with the dynamic context of the containing xsl:merge instruction, while the select attribute is evaluated with the focus for the evaluation as follows:

The bind-source attribute establishes the name of a variable which is available for reference within the xsl:merge-action element, and whose value is a sequence of items, from this source only, that share the composite merge key value for this activation of the xsl:merge-action.

If the sort-before-merge attribute is absent or has the value no, then each input sequence must already be in the correct order for merging (a dynamic error occurs if it is not). If the attribute is present with the value yes, then each input sequence will first be sorted to ensure that it is in the correct order.

Example: Merging Several Documents with the Same Structure

The following xsl:merge-source element selects two anchor items (the root nodes of two documents), and for each of these it selects an input sequence consisting of selected event elements within the relevant document.

<xsl:merge-source for-each="doc('log-A.xml'), doc('log-B.xml')"
                  select="events/event">
   <xsl:merge-key select="@timestamp" order="ascending"/>
</xsl:merge-source>

This example can be extended to merge any number of input documents with the same structure:

<xsl:merge-source for-each="collection('log-collection')"
                  select="events/event">
   <xsl:merge-key select="@time" order="ascending"/>
</xsl:merge-source>

In both the above examples the anchor items are document nodes, and the items in the input sequence are elements within the document that is rooted at this node. This is a common usage pattern, but by no means the only way in which the construct can be used.

The number of anchor items selected by an xsl:merge-source element, and therefore the number of input sequences, is variable, but the input sequences selected by one xsl:merge-source element must all use the same expressions to select the items in the input sequence and to compute their merge keys. If different expressions are needed for different input sequences, then multiple xsl:merge-source elements can be used.

Example: Merging Two Documents with Different Structure

The following code merges two log files having different internal structure:

<xsl:merge-source select="doc('event-log.xml')/*/event">
  <xsl:merge-key select="@timestamp"/>
</xsl:merge-source>
<xsl:merge-source select="doc('error-log.xml')//error">
  <xsl:merge-key select="dateTime(@date, @time)"/>
</xsl:merge-source>

Although the merge keys are computed in different ways for the two input sequences, the keys must be compatible across the two sequences: in this case they are both atomic values of type xs:dateTime.

In the common case where there is only one input sequence of a particular kind, the for-each attribute of xsl:merge-source may be omitted; the select expression is then evaluated relative to the focus of the xsl:merge instruction itself.

Example: Sorting before Merging

Where one or more of the inputs to the merging process is not pre-sorted, a sort can be requested using the sort-before-merge attribute. For example:

<xsl:merge-source select="doc('event-log.xml')/*/event">
  <xsl:merge-key select="@timestamp"/>
</xsl:merge-source>
<xsl:merge-source select="doc('error-log.xml')//error" 
                  sort-before-merge="yes">
  <xsl:merge-key select="dateTime(current-date(), @time)"/>
</xsl:merge-source>

[ERR XTSE3190] It is a static error if two sibling xsl:merge-source elements have the same name, whether explicit or implicit.

15.4 Streamable Merging

Any (zero or more) of the inputs to a merging operation may be designated as streamable by including the attribute streamable="yes" on the xsl:merge-source element.

An xsl:merge instruction is guaranteed-streamable if it satisfies all the following conditions:

  1. The for-each attribute must be present on that xsl:merge-source element, and its value must be a function call that calls the document, docFO30, or collectionFO30 function;

  2. The expression in the select attribute of that xsl:merge-source element must have striding posture;

  3. The sort-before-merge attribute of that xsl:merge-source element must either be absent or take its default value of no;

  4. The select expression of each merge key in that xsl:merge-source element must be a motionless expression;

  5. The sequence constructor in the xsl:merge-action element must have grounded posture and and either motionless or consuming sweep.

Specifying streamable="yes" on an xsl:merge element declares an intent that the xsl:merge instruction should be guaranteed streamable according to these criteria. The consequences of declaring the instruction to be streamable when it is not in fact guaranteed streamable depend on the conformance level of the processor, and are explained in 19.10 Streamability Guarantees.

Example: Streamed Merging

The following example merges two log files, processing each of them using streaming.

<events>
   <xsl:merge bind-group="grp" bind-key="key">
      <xsl:merge-source for-each="doc('log-file-1.xml')" 
                        select="events/event" 
                        streamable="yes">
         <xsl:merge-key select="@timestamp"/>
      </xsl:merge-source>
      <xsl:merge-source for-each="doc('log-files-2.xml')" 
                        select="snapshot(log/day/record)" 
                        streamable="yes">
         <xsl:merge-key select="dateTime(../@date, time)"/>
      </xsl:merge-source>
      <xsl:merge-action>
         <events time="{$key}">
            <xsl:copy-of select="$grp"/>
         </events>   
      </xsl:merge-action>
   </xsl:merge>
</events>

Note the use of the snapshot function. This is needed because the merge key for the second merge source includes data from a child element of the selected element (making it non-motionless) and also from an attribute of the parent element (making it inaccessible if copy-of were used in place of snapshot).

15.5 Defining the Merge Keys

The keys on which the input sequences are sorted are referred to as merge keys. If the attribute sort-before-merge has the value yes, the input sequences will be sorted into the correct sequence before the merge operation takes place (alternatively, the processor may use an algorithm that has the same effect as sorting followed by merging). If the attribute is absent or has the value no, then the input sequences must already be in the correct order.

The merge key for each type of input sequence (that is, for each xsl:merge-source element) is defined by a sequence of xsl:merge-key element children of the xsl:merge-source element. Each xsl:merge-key element defines one merge key component. The syntax and semantics of an xsl:merge-key element are closely based on the rules for the xsl:sort element (the only exception being the absence of the stable attribute); the difference is that xsl:merge-key elements do not cause a sort to take place, they merely declare the existing sort order of the input sequence.

<xsl:merge-key
  select? = expression
  lang? = { language }
  order? = { "ascending" | "descending" }
  collation? = { uri }
  case-order? = { "upper-first" | "lower-first" }
  data-type? = { "text" | "number" | eqname } >
  <!-- Content: sequence-constructor -->
</xsl:merge-key>

The select attribute and the contained sequence constructor are mutually exclusive:

[ERR XTSE3200] It is a static error if an xsl:merge-key element with a select attribute has non-empty content.

The effect of the xsl:merge-key elements is defined in terms of the rules for an equivalent sequence of xsl:sort elements: if the rules for sorting (see 13.1.1 The Sorting Process) with stable="yes" would place an item A before an item B in the sorted sequence produced by the sorting process, then A must precede B in the input sequence to the merging process.

The merge keys of the various input sequences to a merge operation must be compatible with each other, since the merge operation will decide the ordering of the result sequence by comparing merge key values across input sequences. This means that across all the xsl:merge-source children of an xsl:merge instruction:

  • Each xsl:merge-source element must have the same number of xsl:merge-key child elements; let this number be N.

  • For each integer J in 1..N, consider the set of xsl:merge-key elements that are in position J among the xsl:merge-key children of their parent xsl:merge-source element. All the xsl:merge-key elements in this set must have the same effective value for their lang, order, collation, case-order, and data-type attributes, where having the same effective value in this case means that either both attributes must be absent, or both must be present and evaluate to the same value; and in addition in the case of collation the absolute URI must be the same after resolving against the base URI.

If any of the attributes lang, order, collation, case-order, or data-type are attribute value templates, then their effective values are evaluated using the focus of the containing xsl:merge instruction.

[ERR XTSE2200] It is a static error if the number of xsl:merge-key children of a xsl:merge-source element is not equal to the number of xsl:merge-key children of another xsl:merge-source child of the same xsl:merge instruction.

[ERR XTDE2210] It is a dynamic error if there are two xsl:merge-key elements that occupy corresponding positions among the xsl:merge-key children of two different xsl:merge-source elements and that have differing effective values for any of the attributes lang, order, collation, case-order, or data-type. Values are considered to differ if the attribute is present on one element and not on the other, or if it is present on both elements with effective values that are not equal to each other. In the case of the collation attribute, the values are compared as absolute URIs after resolving against the base URI.The error may be reported statically if it is detected statically.

[ERR XTDE2220] It is a dynamic error if any input sequence to an xsl:merge instruction contains two items that are not correctly sorted according to the merge key values defined on the xsl:merge-key children of the corresponding xsl:merge-source element, when compared using the collation rules defined by the attributes of the corresponding xsl:merge-key children of the xsl:merge instruction, unless the attribute sort-before-merge is present with the value yes.

[ERR XTTE2230] It is a type error if some item selected by a particular merge key in one input sequence is not comparable using the XPath le operator with some item selected by the corresponding sort key in another input sequence.

15.6 The xsl:merge-action Element

The xsl:merge-action child of an xsl:merge instruction defines the processing to be applied for each distinct composite merge key value found in the input sequences to the xsl:merge instruction.

<xsl:merge-action>
  <!-- Content: (sequence-constructor) -->
</xsl:merge-action>

The merge key values for each item in an input sequence are calculated based on the corresponding xsl:merge-key elements, in the same way as sort key values are calculated using a sequence of xsl:sort elements (see 13.1.1 The Sorting Process). If several items from the same or from different input sequences have the same values for all their merge keys (comparing pairwise), then they are considered to form a group. The sequence constructor contained in the xsl:merge-action element is evaluated once for each such group of items, and the result of the xsl:merge instruction is the concatenation of the results obtained by processing each group in turn.

The groups are processed one by one, based on the values of the merge keys for the group. If group G has a set of merge key values M, while group H has a set of merge key values N, then in the result of the xsl:merge instruction, the result of processing group G will precede the result of processing H if and only if M precedes N in the sort order defined by the lang, order, collation, case-order, and data-type attributes of the merge key definitions.

Generally, two sets of sort key values are distinct if any corresponding items in the two sets of values do not compare equal under the rules for the XPath eq operator, under the collating rules for the corresponding merge key definition. In rare cases, when considering more than two sets of sort key values, ambiguities may arise because of the non-transitivity of the eq operator when applied across different numeric types. In this situation, the partitioning of items into sets having distinct key values is handled in the same way as for xsl:for-each-group (see 14.5 Non-Transitivity), and is to some extent implementation-dependent.

The static context for the sequence constructor contained within the xsl:merge-action element includes the variables declared using the bind-group and bind-key attributes of the containing xsl:merge instruction and the bind-source attributes of the xsl:merge-source children of this xsl:merge instruction.

[ERR XTSE3270] It is a static error if the set of variable names declared using the bind-group and bind-key attributes of an xsl:merge instruction and the bind-source attributes of its xsl:merge-source children contains any duplicates.

The variable defined in the bind-key attribute, if any, is bound to the value of the composite merge key value. There may be several input items having merge keys that are equal but distinguishable (for example the number 1.0 as a float and as a double, or the strings "A" and "a" under a case-blind collation); in this case the value of the variable is the value of the merge key computed for the first item in the current group, after atomization and casting of xs:untypedAtomic to xs:string.

The variable defined in the bind-group attribute, if any, is bound to the set of items (zero or more from each input sequence) that have this set of values as their merge key value. The value of this variable is referred to as the current group.

Within the current group, the ordering of items from the input sequences is as follows, in major-to-minor order:

  • Items are first ordered by the xsl:merge-source element that defined the input sequence from which the item was taken; items from xsl:merge-source A precede items from xsl:merge-source B if A precedes B in document order within the stylesheet.

  • Items from different input sequences selected by the same xsl:merge-source element are then ordered based on the order of the anchor items in the sequence selected by evaluating the select attribute of the xsl:merge-source element.

  • Finally, duplicate items from the same input sequence retain their order from the input sequence.

Duplicates are not eliminated: for example, if the same node is selected in more than one input sequence, it may appear twice in the current group.

The variable defined in the bind-source attribute of an xsl:merge-source element, if any, is bound to the current group, filtered to include only those items that originate from the merge source in question.

The focus for evaluation of the sequence constructor contained in the xsl:merge-action element is as follows:

  • The context item is the first item in the current group, that is current-group()[1]

  • The context position is the position of the current group within the sequence of groups (so the first evaluation of xsl:merge-action has position()=1, the second has position()=2, and so on).

  • The context size is the number of groups, that is, the number of distinct sets of merge key values.

Example: Selective Processing of Merge Inputs

Consider a situation where there are two merge sources, named "master" and "update"; the master source identifies a single merge input file (the master file), while the update source identifies a set of N update files, perhaps one for each day of the week. The required logic is that if a merge key is present only in the master file, then the corresponding item should be copied to the output; if it is present in a single update file then that item replaces the corresponding item from the master file; if it is present in several update files, then an error is raised. This can be achieved as follows:

<xsl:merge>
  <xsl:merge-source bind-source="master" 
                    for-each="doc('master.xml')"
                    select="/events/event">
      <xsl:merge-key select="@key"/>
  </xsl:merge-source>
  <xsl:merge-source bind-source="updates" 
                    for-each="collection('updates')"
                    select="/events/event-change">
      <xsl:merge-key select="@affected-key"/>
  </xsl:merge-source>
  <xsl:merge-action>
    <xsl:choose>
      <xsl:when test="empty($master)">
        <xsl:message>
           Error: update is present with no matching master record!
        </xsl:message>
      </xsl:when>
      <xsl:when test="empty($updates)">
        <xsl:copy-of select="$master"/>
      </xsl:when>
      <xsl:when test="count($updates) = 1">
        <xsl:copy-of select="$updates"/>
      </xsl:when>
      <xsl:otherwise>
        <xsl:message>
           Conflict: multiple updates for the same master record!
        </xsl:message>
      </xsl:otherwise>
    </xsl:choose>
  </xsl:merge-action>
</xsl:merge>
            

Some words of explanation:

  • Error messages are produced if there is an update element whose key does not correspond to any element in the master source, or if there is more than one update element corresponding to the same master element.

  • In the absence of errors, if there is a single update element then it is copied to the output; if there is none, then the master element is copied.

15.7 Examples of xsl:merge

Previous sections introduced examples designed to illustrate some specific features of the xsl:merge instruction. This section provides some further examples to illustrate different ways in which the instruction can be used.

Example: Applying Transactions to a Master File

This example applies transactions from a transaction file to a master file. Records in the master file for which there is no corresponding transaction are copied unchanged. The transaction file contains instructions to delete, replace, or insert records identified by an ID value. The master file is known to be sorted on the ID value; the transaction file is unsorted.

Master file document structure:

<data>
  <record ID="A0001"><...></record>
  <record ID="A0002"><...></record>
  <record ID="A0003"><...></record>
</data>

Transaction file document structure:

<transactions>
  <update record="A0004" action="insert"><...></update>
  <update record="A0002" action="delete"/>
  <update record="A0003" action="replace"><...></update>
</transactions>

Solution:

 <xsl:merge bind-key="merge-key">
  <xsl:merge-source bind-source="master"
                    select="doc('master.xml')/data/record">
      <xsl:merge-key select="@ID"/>
  </xsl:merge-source>
  <xsl:merge-source bind-source="updates"
                    sort-before-merge="yes"
                    select="doc('transactions.xml')/transactions/update">     
      <xsl:merge-key select="@record"/>
  </xsl:merge-source>
  <xsl:merge-action>
    <xsl:choose>
      <xsl:when test="empty($updates)">
        <xsl:copy-of select="$master"/>
      </xsl:when>
      <xsl:when test="$updates/@action=('insert', 'replace')">
        <record ID="{$merge-key}">
          <xsl:copy-of select="$update/*"/>
        </record>
      </xsl:when>
      <xsl:when test="$updates/@action='delete'"/>
    </xsl:choose>
  </xsl:merge-action>
  </xsl:merge>

 

Example: Merging Two Sequences of Numbers

The xsl:merge instruction can be used to determine the union, intersection, or difference of two sequences of numbers (or other atomic values). This code gives the union:

<xsl:merge bind-key="k">
  <xsl:merge-source select="1 to 30">
      <xsl:merge-key select="."/>
  </xsl:merge-source>
  <xsl:merge-source select="20 to 40">
      <xsl:merge-key select="."/>
  </xsl:merge-source>
  <xsl:merge-action>
    <xsl:value-of select="$k"/>
  </xsl:merge-action>
</xsl:merge>
               

While this gives the intersection:

<xsl:merge bind-key="k" bind-group="g">
  <xsl:merge-source select="1 to 30">
      <xsl:merge-key select="."/>
  </xsl:merge-source>
  <xsl:merge-source select="20 to 40">
      <xsl:merge-key select="."/>
  </xsl:merge-source>
  <xsl:merge-action>
    <xsl:if test="count($g) eq 2">
      <xsl:value-of select="$k"/>
    </xsl:if>
  </xsl:merge-action>
</xsl:merge>
               

16 Splitting

Sometimes it is convenient to be able to compute multiple results during a single scan of the input data. For example, a transformation may wish to rename selected elements, and also to output a count of how many elements have been renamed. Traditionally in a functional language this means computing two separate functions of the input sequence, which (in the absence of sophisticated optimization) will result in the input being scanned twice. This is inconsistent with streaming, where the input is only available to be scanned once, and it can also lead to poor performance in non-streaming applications.

To meet this requirement, XSLT 3.0 introduces the instruction xsl:fork. The content of this instruction is a restricted form of sequence constructor, and in a formal sense the effect of the instruction is simply to return the result of evaluating the sequence constructor. However, the presence of the instruction affects the analysis of streamability (see 19 Streamability). In particular, when xsl:fork is used in a context where streaming is required, each independent instruction within the sequence constructor must be streamable, but the analysis assumes that these instructions can all be evaluated during a single pass of the streamed input document.

Note:

The semantics of the instruction require a number of result sequences to be computed during a single pass of the input. A processor may interpret this as a request to use multiple threads. However, implementations using a single thread are feasible, and this instruction is not intended primarily as a means for stylesheet authors to express their intentions with regard to multi-threaded execution.

Note:

Because multiple results are computed during a single pass of the input, and then concatenated into a single sequence, this instruction will generally involve some buffering of results. The amount of memory used should not exceed that needed to hold the results of the instruction. However, within this principle, implementations may adopt a variety of strategies for evaluation; for example, there may be cases where buffering of the input is more efficient than buffering of output.

Generally, stylesheet authors indicate that buffering of input is the preferred strategy by using the copy-of or snapshot functions, and indicate that buffering of output is preferred by using xsl:fork. However, conformant processors are not constrained in their choice of evaluation strategies.

The following section describes the xsl:fork instruction more formally.

16.1 The xsl:fork Instruction

<!-- Category: instruction -->
<xsl:fork>
  <!-- Content: ((xsl:sequence | xsl:fallback))+ -->
</xsl:fork>

The result of the xsl:fork instruction is the sequence formed by concatenating the results of evaluating each of its contained xsl:sequence instructions, in order. That is, the result can be determined by treating the content as a sequence constructor and evaluating it as such.

Note:

Any xsl:fallback children will be ignored by an XSLT 3.0 processor.

By using the xsl:fork instruction, the stylesheet author is suggesting to the processor that it would be beneficial to evaluate the contained xsl:sequence instructions during a single pass of a streamed input document. The processor is not required to take any notice of this suggestion.

The presence of an xsl:fork instruction affects the analysis of streamability, as described in 19 Streamability.

16.2 Examples of Splitting with Streamed Data

This section gives examples of how splitting using xsl:fork can be used to enable streaming of input documents in cases where several results need to be computed during a single pass over the input data.

Example: Splitting a Transaction File

Consider a transaction file that contains a sequence of debits and credits:

<transactions>
  <transaction value="5.60"/>
  <transaction value="11.20"/>
  <transaction value="-3.40"/>
  <transaction value="8.90"/>
  <transaction value="-1.99"/>
</transactions>

where the requirement is to split this into two separate files containing credits and debits respectively.

This can be achieved in guaranteed-streamable code as follows:

<xsl:stream href="transactions.xml">
  <xsl:fork>
    <xsl:sequence>
      <xsl:result-document href="credits.xml">
        <credits>
          <xsl:for-each select="transactions/transaction[@value ge 0]">
            <xsl:copy-of select="."/>
          </xsl:for-each>
        </credits>
      </xsl:result-document>
    </xsl:sequence>
    <xsl:sequence>
      <xsl:result-document href="debits.xml">
        <debits>
          <xsl:for-each select="transactions/transaction[@value lt 0]">
            <xsl:copy-of select="."/>
          </xsl:for-each>
        </debits>
      </xsl:result-document>
    </xsl:sequence>  
  </xsl:fork>
</xsl:stream>
               

In the absence of the xsl:fork instruction, this would not be streamable, because the sequence constructor includes two consuming instructions. With the addition of the xsl:fork instruction, however, each xsl:result-document instruction is allowed to make a downwards selection.

One possible implementation model for this is as follows: a single thread reads the source document, and sends parsing events such as start-element and end-element to two other threads, each of which is writing one of the two result documents. Each of these implements the downwards-selecting path expression using a process that waits until the next transaction start-element event is received; when this event is received, the process examines the @value attribute to determine whether or not this transaction is to be copied; if it is, then all events until the matching transaction end-element event are copied to the serializer for the result document; otherwise, these events are discarded.

 

Example: Arithmetic using Multiple Child Elements as Operands

The rules for streamability do not allow two instructions in a sequence constructor to both read child or descendant elements of the context node, which makes it tricky to perform a calculation in which multiple child elements act as operands. This restriction can be avoided by using xsl:fork, as shown below, where each of the two branches of the xsl:fork instruction selects children of the context node.

<xsl:template match="order" mode="a-streamable-mode">                  
  <xsl:variable name="price-and-discount" as="xs:decimal+">
    <xsl:fork>
      <xsl:sequence select="xs:decimal(price)"/>
      <xsl:sequence select="xs:decimal(discount)"/>
    </xsl:fork>
  </xsl:variable>
  <xsl:value-of select="$price-and-discount[1] - $price-and-discount[2]"/>
  </xsl:template>

A possible implementation strategy here is for events from the XML parser to be sent to two separate agents (perhaps but not necessarily running in different threads), one of which computes xs:decimal(price) and the other xs:decimal(discount); on completion the results computed by the two agents are appended to the sequence that forms the value of the variable.

With this strategy, the processor would require sufficient memory to hold the results of evaluating each branch of the fork. If these results (unlike this example) are large, this could defeat the purpose of streaming by requiring large amounts of memory; nevertheless, this code is treated as streamable.

Note:

An alternative solution to this requirement is to use map expressions: see 21.1.4 Map Expressions.

 

Example: Deleting Elements, and Counting Deletions

In this example the input is a narrative document containing note elements at any level of nesting. The requirement is to output a copy of the input document in which (a) the note elements have been removed, and (b) a footnote is added at the end indicating how many note elements have been deleted.

<xsl:mode on-no-match="shallow-copy" streamable="yes"/>

<xsl:template match="note"/>

<xsl:template match="/*">
  <xsl:fork>
    <xsl:sequence>
      <xsl:apply-templates/>
    </xsl:sequence>
    <xsl:sequence>
      <footnote>
        <p>Removed <xsl:value-of select="count(.//note)"/> 
                 note elements.</p>
      </footnote>
    </xsl:sequence>  
  </xsl:fork>
</xsl:template>
               

The xsl:fork instruction contains two independent branches. These can therefore be evaluated in the same pass over the input data. The first branch (the xsl:apply-templates instruction) causes everything except the note elements to be copied to the result; the second instruction (the literal result element footnote) outputs a count of the number of descendant note elements.

Note that although the processing makes a single pass over the input stream, there is some buffering of results required, because the results of the instructions within the xsl:fork instruction need to be concatenated. In this case an intelligent implementation might be able to restrict the buffered data to a single integer.

In a formal sense, however, the result is exactly the same as if the xsl:fork element were not there.

An alternative way of solving this example problem would be to count the number of note elements using an accumulator: see 18.2 Accumulators.

17 Regular Expressions

The core function library for XPath 3.0 defines three basic functions that make use of regular expressions:

These functions are described in [Functions and Operators].

For more complex string processing than is possible using these functions, XSLT provides an instruction xsl:analyze-string, which is defined in this section.

The regular expressions used by this instruction, and the flags that control the interpretation of these regular expressions, must conform to the syntax defined in [Functions and Operators] (see Section 5.6.1 Regular expression syntax FO30), which is itself based on the syntax defined in [XML Schema Part 2].

Note:

XPath 3.0 adds a fourth function, analyze-stringFO30, whose functionality is closely modeled on the xsl:analyze-string instruction described in this section, repackaging the facilities in the form of a function.

17.1 The xsl:analyze-string Instruction

<!-- Category: instruction -->
<xsl:analyze-string
  select = expression
  regex = { string }
  flags? = { string } >
  <!-- Content: (xsl:matching-substring?, xsl:non-matching-substring?, xsl:fallback*) -->
</xsl:analyze-string>

<xsl:matching-substring>
  <!-- Content: sequence-constructor -->
</xsl:matching-substring>

<xsl:non-matching-substring>
  <!-- Content: sequence-constructor -->
</xsl:non-matching-substring>

The xsl:analyze-string instruction takes as input a string (the result of evaluating the expression in the select attribute) and a regular expression (the effective value of the regex attribute).

If the result of evaluating the select expression is an empty sequence, it is treated as a zero-length string. If the value is not a string, it is converted to a string by applying the function conversion rules.

The flags attribute may be used to control the interpretation of the regular expression. If the attribute is omitted, the effect is the same as supplying a zero-length string. This is interpreted in the same way as the $flags attribute of the functions matchesFO30, replaceFO30, and tokenizeFO30. Specifically, if it contains the letter m, the match operates in multiline mode. If it contains the letter s, it operates in dot-all mode. If it contains the letter i, it operates in case-insensitive mode. If it contains the letter x, then whitespace within the regular expression is ignored. For more detailed specifications of these modes, see [Functions and Operators] (Section 5.6.1.1 Flags FO30).

Note:

Because the regex attribute is an attribute value template, curly brackets within the regular expression must be doubled. For example, to match a sequence of one to five characters, write regex=".{{1,5}}". For regular expressions containing many curly brackets it may be more convenient to use a notation such as regex="{'[0-9]{1,5}[a-z]{3}[0-9]{1,2}'}", or to use a variable.

The xsl:analyze-string instruction may have two child elements: xsl:matching-substring and xsl:non-matching-substring. Both elements are optional, and neither may appear more than once. At least one of them must be present. If both are present, the xsl:matching-substring element must come first.

The content of the xsl:analyze-string instruction must take one of the following forms:

  1. A single xsl:matching-substring instruction, followed by zero or more xsl:fallback instructions

  2. A single xsl:non-matching-substring instruction, followed by zero or more xsl:fallback instructions

  3. A single xsl:matching-substring instruction, followed by a single xsl:non-matching-substring instruction, followed by zero or more xsl:fallback instructions

[ERR XTSE1130] It is a static error if the xsl:analyze-string instruction contains neither an xsl:matching-substring nor an xsl:non-matching-substring element.

Any xsl:fallback elements among the children of the xsl:analyze-string instruction are ignored by an XSLT 2.0 or 3.0 processor, but allow fallback behavior to be defined when the stylesheet is used with an XSLT 1.0 processor operating with forwards-compatible behavior.

This instruction is designed to process all the non-overlapping substrings of the input string that match the regular expression supplied.

[ERR XTDE1140] It is a dynamic error if the effective value of the regex attribute does not conform to the required syntax for regular expressions, as specified in [Functions and Operators]. If the regular expression is known statically (for example, if the attribute does not contain any expressions enclosed in curly brackets) then the processor may signal the error as a static error.

[ERR XTDE1145] It is a dynamic error if the effective value of the flags attribute has a value other than the values defined in [Functions and Operators]. If the value of the attribute is known statically (for example, if the attribute does not contain any expressions enclosed in curly brackets) then the processor may signal the error as a static error.

To explain the behavior of the instruction it is useful to consider an input string of length N characters as having N+1 inter-character positions, including one just before the first character and one just after the last. Each of these positions is a possible position for testing whether the regular expression matches. These positions are numbered from zero to N.

Note:

The term character, here as elsewhere in this specification, means a Unicode codepoint. When strings are held in decomposed form, the multiple codepoints representing a composite character are considered to be multiple characters. A codepoint greater than 65535 is considered as one character, not as a surrogate pair.

The processor starts by setting the current position to position zero, and the current non-matching substring to a zero-length string. It then does the following repeatedly:

  1. Test whether the regular expression matches at the current position.

  2. If there is a match:

    1. If the current non-matching substring has length greater than zero, evaluate the xsl:non-matching-substring sequence constructor with the current non-matching substring as the context item.

    2. Reset the current non-matching substring to a zero-length string.

    3. Evaluate the xsl:matching-substring sequence constructor with the matching substring as the context item.

    4. Do the appropriate one of of the following:

      1. If the matching substring is non-zero length, set the current position to coincide with the end of the matching substring, exit, and repeat.

      2. If the matching substring is zero length and the current position is at the end of the input string, exit.

      3. If the matching substring is zero length and the current position is not at the end of the input string, add the character that immediately follows the current position to the current non-matching substring, set the current position to the position immediately after this character, exit, and repeat.

  3. If there is no match:

    1. If the current position is the last position (that is, just after the last character):

      1. If the current non-matching substring has length greater than zero, evaluate the xsl:non-matching-substring sequence constructor with the current non-matching substring as the context item.

      2. Exit.

    2. Otherwise, add the character at the current position to the current non-matching substring, increment the current position, and repeat.

When the matcher is looking for a match at a particular starting position and there are several alternatives within the regular expression that match at this position in the input string, then the match that is chosen is the first alternative that matches. For example, if the input string is The quick brown fox jumps and the regular expression is jump|jumps, then the match that is chosen is jump.

The input string is thus partitioned into a sequence of substrings, some of which match the regular expression, others which do not match it. Each non-matching substring will contain at least one character, but a matching substring may be zero-length. This sequence of substrings is processed using the instructions within the contained xsl:matching-substring and xsl:non-matching-substring elements. A matching substring is processed using the xsl:matching-substring element, a non-matching substring using the xsl:non-matching-substring element. Each of these elements takes a sequence constructor as its content. If the element is absent, the effect is the same as if it were present with empty content. In processing each substring, the contents of the substring will be the context item (as a value of type xs:string); the position of the substring within the sequence of matching and non-matching substrings will be the context position; and the number of matching and non-matching substrings will be the context size.

17.2 fn:regex-group

Summary

Returns the string captured by a parenthesized subexpression of the regular expression used during evaluation of the xsl:analyze-string instruction.

Signature

regex-group($group-number as xs:integer) as xs:string
Properties

This function is deterministicFO30, context-dependentFO30, and focus-independentFO30.

Rules

[Definition: While the xsl:matching-substring instruction is active, a set of current captured substrings is available, corresponding to the parenthesized sub-expressions of the regular expression.] These captured substrings are accessible using the function regex-group. This function takes an integer argument to identify the group, and returns a string representing the captured substring.

The Nth captured substring (where N > 0) is the string matched by the subexpression contained by the Nth left parenthesis in the regex, excluding any non-capturing groups, which are written as (?:xxx). The zeroeth captured substring is the string that matches the entire regex. This means that the value of regex-group(0) is initially the same as the value of . (dot).

The function returns the zero-length string if there is no captured substring with the relevant number. This can occur for a number of reasons:

  1. The number is negative.

  2. The regular expression does not contain a parenthesized sub-expression with the given number.

  3. The parenthesized sub-expression exists, and did not match any part of the input string.

  4. The parenthesized sub-expression exists, and matched a zero-length substring of the input string.

The set of captured substrings is a context variable with dynamic scope. It is initially an empty sequence. During the evaluation of an xsl:matching-substring instruction it is set to the sequence of matched substrings for that regex match. During the evaluation of an xsl:non-matching-substring instruction or a pattern or a stylesheet function it is set to an empty sequence. On completion of an instruction that changes the value, the variable reverts to its previous value.

The value of the current captured substrings is unaffected through calls of xsl:apply-templates, xsl:call-template, xsl:apply-imports or xsl:next-match, or by expansion of named attribute sets.

17.3 Examples of Regular Expression Matching

Example: Replacing Characters by Elements

Problem: replace all newline characters in the abstract element by empty br elements:

Solution:

<xsl:analyze-string select="abstract" regex="\n">
  <xsl:matching-substring>
    <br/>
  </xsl:matching-substring>
  <xsl:non-matching-substring>
    <xsl:value-of select="."/>
  </xsl:non-matching-substring>
</xsl:analyze-string>

 

Example: Recognizing non-XML Markup Structure

Problem: replace all occurrences of [...] in the body by cite elements, retaining the content between the square brackets as the content of the new element.

Solution:

<xsl:analyze-string select="body" regex="\[(.*?)\]">
  <xsl:matching-substring>
    <cite><xsl:value-of select="regex-group(1)"/></cite>
  </xsl:matching-substring>
  <xsl:non-matching-substring>
    <xsl:value-of select="."/>
  </xsl:non-matching-substring>
</xsl:analyze-string>

Note that this simple approach fails if the body element contains markup that needs to be retained. In this case it is necessary to apply the regular expression processing to each text node individually. If the [...] constructs span multiple text nodes (for example, because there are elements within the square brackets) then it probably becomes necessary to make two or more passes over the data.

 

Example: Parsing a Date

Problem: the input string contains a date such as 23 March 2002. Convert it to the form 2002-03-23.

Solution (with no error handling if the input format is incorrect):

<xsl:variable name="months" 
        select="'January', 'February', 'March', ..."/>

<xsl:analyze-string select="normalize-space($input)" 
    regex="([0-9]{{1,2}})\s([A-Z][a-z]+)\s([0-9]{{4}})">
    <xsl:matching-substring>
        <xsl:number value="regex-group(3)" format="0001"/>          
        <xsl:text>-</xsl:text>
        <xsl:number value="index-of($months, regex-group(2))" format="01"/>
        <xsl:text>-</xsl:text>
        <xsl:number value="regex-group(1)" format="01"/>
    </xsl:matching-substring>
</xsl:analyze-string>

Note the use of normalize-space to simplify the work done by the regular expression, and the use of doubled curly brackets because the regex attribute is an attribute value template.

 

Example: Matching Zero-Length Strings

This example removes all empty and whitespace-only lines from a file.

<xsl:analyze-string select="unparsed-text('in.txt')"
                    regex="^[\t ]*$" flags="m" expand-text="yes">
  <xsl:non-matching-substring>{.}</xsl:non-matching-substring>
</xsl:analyze-string>

 

Example: Parsing comma-separated values

There are many variants of CSV formats. This example is designed to handle input where:

  • Each record occupies one line.

  • Fields are separated by commas.

  • Quotation marks around a field are optional, unless the field contains a comma or quotation mark, in which case they are mandatory.

  • A quotation mark within the value of a field is represented by a pair of two adjacent quotation marks.

For example, the input record:

Ten Thousand,10000,,"10,000","It's ""10 Grand"", mister",10K

contains six fields, specifically:

  • Ten Thousand

  • 10000

  • <zero-length-string>

  • 10,000

  • It's "10 Grand", mister

  • 10K

The following code parses such CSV input into an XML structure containing row and col elements:

<xsl:for-each select="unparsed-text-lines('in.csv')" expand-text="yes">
  <row>
    <xsl:analyze-string select="." 
                        regex='(?:^|,)(?:"((?:[^"]|"")*)"|([^",]*))'>
      <xsl:matching-substring>
        <col>{replace(regex-group(1), '""', '"')||regex-group(2)}</col>
      </xsl:matching-substring>
    </xsl:analyze-string>
  </row>
</xsl:for-each>

Note that because this regular expression matches a zero-length string, it is not permitted in XSLT 2.0.

18 Streaming

XSLT 3.0 introduces a number of constructs that are specifically designed to enable streamed applications to be written, but which are also useful in their own right; it also includes some features that are very specialized to streaming. The constructs in this latter category are described in this section.

18.1 The xsl:stream Instruction

<!-- Category: instruction -->
<xsl:stream
  href = { uri }
  validation? = "strict" | "lax" | "preserve" | "strip"
  type? = eqname >
  <!-- Content: sequence-constructor -->
</xsl:stream>

The xsl:stream instruction reads a source document whose URI is supplied, and processes the content of the document using streaming by evaluating the contained sequence constructor.

For example, if a document represents a book holding a sequence of chapters, then the following code can be used to split the book into multiple XML files, one per chapter, without allocating memory to hold the entire book in memory at one time:

<xsl:stream href="book.xml">
  <xsl:for-each select="book">             
    <xsl:for-each select="chapter">
      <xsl:result-document href="chapter{position()}.xml">
        <xsl:copy-of select="."/>
      </xsl:result-document>
    </xsl:for-each>
  </xsl:for-each>  
</xsl:stream>

The document to be read is determined by the effective value of the href attribute (which is defined as an attribute value template). This must be a valid URI reference. If it is an absolute URI reference, it is used as is; if it is a relative URI reference, it is made absolute by resolving it against the base URI of the xsl:stream element. The process of obtaining a document node given a URI is the same as for the docFO30 function. However, unlike the docFO30 function, the xsl:stream instruction offers no guarantee that the resulting document will be stable (that is, that multiple calls specifying the same URI will return the same document).

Specifically, if the xsl:stream instruction is evaluated several times (or if different xsl:stream instructions are evaluated) with the same URI (after making it absolute) as the value of the href attribute, it is implementation-dependent whether the same nodes or different nodes are returned on each occasion; it is also possible that the actual document content will be different.

The result of the xsl:stream instruction is the same as the result of the following (non-streaming) process:

  1. The source document is read from the supplied URI and parsed to form an instance of the XDM data model. This is the streamed document.

  2. The contained sequence constructor is evaluated with the document node of the streamed document as the context item, and with the context position and context size set to one, and the resulting sequence is returned as the result of the xsl:stream instruction.

The xsl:stream instruction is guaranteed-streamable if the contained sequence constructor is grounded, as assessed using the streamability analysis in 19 Streamability. The consequences of being or not being guaranteed streamable depend on the processor conformance level, and are explained in 19.10 Streamability Guarantees.

Note:

The name of the instruction reflects its intended usage, to process an input document using streaming. However, a processor that does not offer the streaming feature must still implement the instruction (without being required to use streamed evaluation or to check its streamability); and processors that do offer the streaming feature are also required to provide a mode of execution in which the construct is evaluated without streaming if it fails the streamability criteria.

Note:

The rules for streamability ensure that the sequence constructor (and therefore the xsl:stream instruction) cannot return any nodes from the streamed document. For example, it cannot contain the instruction <xsl:sequence select="//chapter"/>. If nodes from this document are to be returned, they must first be copied, for example by using the xsl:copy-of instruction or by calling the copy-of or snapshot functions.

Because the xsl:stream instruction cannot return nodes from the streamed document, any nodes it does return will be conventional (unstreamed) nodes that can be processed without restriction. For example, if xsl:stream is invoked within a stylesheet function f:firstChapter, and the sequence constructor consists of the instruction <xsl:copy-of select="//chapter"/>, then the calling code can manipulate the resulting chapter elements as ordinary trees rooted at parentless element nodes.

18.1.1 Validation of Streamed Documents

The validation and type attributes of xsl:stream may be used to control schema validation of the streamed document. They have the same effect as the corresponding attributes of the xsl:copy-of instruction when applied to a document node, except that the copy that is produced is itself a streamed document. The process is described in more detail in 24.2.2 Validating Document Nodes.

These two attributes are both optional, and if one is specified then the other must be omitted.

The presence of a validation or type attribute on an xsl:stream instruction causes any input-type-annotations attribute to have no effect on any document read using that instruction.

Note:

In effect, setting validation to strict or lax, or supplying the type attribute, requests document-level validation of the input as it is read. Setting validation="preserve" indicates that if the incoming document contains type annotations (for example, produced by validating the output of a previous step in a streaming pipeline) then they should be retained, while the value strip indicates that any such type annotations should be dropped.

It is a consequence of the way validation is defined in XSD that the type annotation of an element node can be determined during the processing of its start tag, although the actual validity of the element is not known until the end tag is encountered. When validation is requested, a streamed document should not present data to the stylesheet except to the extent that such data could form the leading part of a valid document. If the document proves to be invalid, the processor should not pass invalid data to the stylesheet to be processed, but should immediately signal the appropriate error. For the purposes of xsl:try and xsl:catch, this error can only be caught at the level of the xsl:stream instruction that initiated validation, not at a finer level. If validation errors are caught in this way, any output that has been computed up to the point of the error is not added to the final result tree; the mechanisms to achieve this may use memory, which may reduce the efficacy of streaming.

The analyis of guaranteed streamability (see 19 Streamability) takes no account of information that might be obtained from a schema-aware static analysis of the stylesheet. Implementations may, however, be able to use streaming strategies for stylesheets that are not guaranteed-streamable, by taking advantage of such information. For example, an implementation might be able to treat the expression .//title as striding rather than crawling if it can establish from knowledge of the schema that two title elements will never overlap.

18.1.2 Examples of xsl:stream

The xsl:stream instruction can be used to initiate processing of a document using streaming with a variety of coding styles, illustrated in the examples below.

Example: Using xsl:stream with Aggregate Functions

The following example computes the number of transactions in a transaction file

Input:

<transactions>
  <transaction value="12.51"/>
  <transaction value="3.99"/>
</transactions>

Stylesheet code:

<xsl:stream href="transactions.xml">
  <count>
    <xsl:value-of select="count(transactions/transaction)"/>
  </count>
</xsl:stream>

Result:

<count>2</count>

Analysis:

  1. The literal result element count has the same sweep as the xsl:value-of instruction.

  2. The xsl:value-of instruction has the same sweep as its select expression.

  3. The call to count has the same sweep as its argument.

  4. The argument to count is a RelativePathExpr that takes the form of a motionless pattern and appears in an inspection context (the argument to count()); the sweep of the RelativePathExpr and therefore of the entire body of the xsl:stream instruction is therefore consuming.

The following example computes the highest-value transaction in the same input file:

<xsl:stream href="transactions.xml">
  <maxValue>
    <xsl:value-of select="max(transactions/transaction/@value)"/>
  </maxValue>
</xsl:stream>

Result:

<maxValue>12.51</maxValue>

Analysis:

  1. The literal result element maxValue has the same sweep as the xsl:value-of instruction.

  2. The xsl:value-of instruction has the same sweep as its select expression.

  3. The call to max has the same sweep as its argument.

  4. The argument to max is a RelativePathExpr whose two operands are the RelativePathExpr transactions/transaction and the AxisStep @value. The first operand transactions/transaction has striding posture. The second operand @value, given that it appears in a node value context, is motionless. The RelativePathExpr argument to max is therefore consuming.

  5. The entire body of the xsl:stream instruction is therefore consuming.

To compute both the count and the maximum value in a single pass over the input, it is possible to use two variables.

 

Example: Using xsl:stream with xsl:for-each to Process a Collection of Input Documents

This example displays a list of the chapter titles extracted from each book in a collection of books.

Each input document is assumed to have a structure such as:

<book>
  <chapter number-of-pages="18">
    <title>The first chapter of book A</title>
    ...
  </chapter>
  <chapter number-of-pages="15">
    <title>The second chapter of book A</title>
    ...
  </chapter>
  <chapter number-of-pages="12">
    <title>The third chapter of book A</title>
    ...
  </chapter>
</book>

Stylesheet code:

<chapter-titles>
  <xsl:for-each select="uri-collection('books')">
    <xsl:stream href="{.}">
      <xsl:for-each select="book">
        <xsl:for-each select="chapter">
           <title><xsl:value-of select="title"/></title>
        </xsl:for-each>
      </xsl:for-each>
    </xsl:stream>
  </xsl:for-each>
</chapter-titles>

Output:

<chapter-titles>
  <title>The first chapter of book A</title>
  <title>The second chapter of book A</title>
  ...
  <title>The first chapter of book B</title>
  ...
</chapter-titles>

Note:

This example uses the function uri-collectionFO30 to obtain the document URIs of all the documents in a collection, so that each one can be processed in turn using xsl:stream.

 

Example: Using xsl:stream with xsl:iterate

This example assumes that the input is a book with multiple chapters, as shown in the previous example, with the page count for each chapter given as an attribute of the chapter. The transformation determines the starting page number for each chapter by accumulating the page counts for previous chapters, and rounding up to an odd number if necessary.

<chapter-start-page>
   <xsl:stream href="book.xml">
      <xsl:iterate select="book/chapter">
         <xsl:param name="start-page" select="1"/>
         <chapter title="{title}" start-page="{$start-page}"/>
         <xsl:next-iteration>
            <xsl:with-param name="start-page" 
                            select="$start-page + @number-of-pages + 
                                      (@number-of-pages mod 2)"/>
         </xsl:next-iteration>
      </xsl:iterate>
   </xsl:stream>
</chapter-start-page>

Output:

<chapter-start-page>
  <chapter title="The first chapter of book A" start-page="1"/>
  <chapter title="The second chapter of book A" start-page="19"/>
  <chapter title="The third chapter of book A" start-page="35"/>
  ...
</chapter-start-page>
                     

 

Example: Using xsl:stream with xsl:for-each-group

This example assumes that the input is a book with multiple chapters, and that each chapter belongs to a part, which is present as an attribute of the chapter (for example, chapters 1-4 might constitute Part 1, the next three chapters forming Part 2, and so on):

<book>
  <chapter part="1">
    <title>The first chapter of book A</title>
    ...
  </chapter>
  <chapter part="1">
    <title>The second chapter of book A</title>
    ...
  </chapter>
  ...
  <chapter part="2">
    <title>The fifth chapter of book A</title>
    ...
  </chapter>
</book>

The transformation copies the full text of the chapters, creating an extra level of hierarchy for the parts.

<book>
   <xsl:stream href="book.xml">
      <xsl:for-each select="book">
         <xsl:for-each-group select="chapter" group-adjacent="data(@part)"
                             bind-group="g" bind-grouping-key="k">
            <part number="{$k}">
               <xsl:copy-of select="$g"/>
            </part>
         </xsl:for-each-group>
      </xsl:for-each>
   </xsl:stream>
</book>

Output:

<book>
  <part number="1">
    <chapter title="The first chapter of book A" part="1">
      ...
    </chapter>
    <chapter title="The second chapter of book A" part="1">
      ...
    </chapter>
    ...
  </part>
  <part number="2">
    <chapter title="The fifth chapter of book A" part="2">
    ...
    </chapter>
    ...
  </part>
</book>
    

 

Example: Using xsl:stream with xsl:apply-templates

This example copies an XML document while deleting all the ednote elements at any level of the tree, together with their descendants. This example is a complete stylesheet, which is intended to be evaluated by nominating main as the initial template. The use of on-no-match="deep-copy" in the xsl:mode declaration means that the built-in template rule copies nodes unchanged, except where overridden by a user-defined template rule.

<xsl:transform version="3.0" 
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:mode name="delete-ednotes" streamable="yes" 
                                on-no-match="shallow-copy"/>

<xsl:template name="main">
   <xsl:stream href="book.xml">
      <xsl:apply-templates mode="delete-ednotes"/>
   </xsl:stream>
</xsl:template>

<xsl:template match="ednote" mode="delete-ednotes"/>

</xsl:transform>

Additional template rules could be added to process other elements and attributes in the same pass through the data: for example, to modify the value of a last-updated attribute (wherever it appears) to the current date and time, the following rule suffices:

<xsl:template match="@last-updated">
  <xsl:attribute name="last-updated" select="current-dateTime()"/>
</xsl:template>

18.2 Accumulators

Accumulators are introduced in XSLT 3.0 to enable data that is read during streamed processing of a document to be accumulated, processed or retained for later use. However, they may equally be used with non-streamed processing.

[Definition: An accumulator defines a value that is computed progressively while processing the nodes of a document in document order. The value for a given node is available via a pair of functions, one giving the value for a node before processing its descendants, and one giving the value for the same node after processing its descendants.]

The following sections give first, the syntax rules for defining an accumulator; then an informal description of the semantics; then a more formal definition; and finally, examples. But to illustrate the concept intuitively, the following simple example shows how an accumulator can be used for numbering of nodes:

Example: Numbering Figures within a Chapter

This example assumes document input in which figure elements can appear within chapter elements (which we assume are not nested), and the requirement is to render the figures with a caption that includes the figure number within its containing chapter.

When the document is processed using streaming, the xsl:number instruction is not available, so a solution using accumulators is needed.

The required accumulator can be defined and used like this:

   <xsl:accumulator name="figNr" as="xs:integer" 
                    initial-value="0" streamable="yes">
     <xsl:accumulator-rule match="chapter" new-value="0"/>
     <xsl:accumulator-rule match="figure" new-value="$value + 1"/>
   </xsl:accumulator>
   
   <xsl:mode streamable="yes"/>
   <xsl:template match="figure">
     <xsl:apply-templates/>
     <p>Figure <xsl:value-of select="accumulator-before('figNr')"/></p>
   </xsl:template>  
                  

18.2.1 Declaring an Accumulator

<!-- Category: declaration -->
<xsl:accumulator
  name = eqname
  initial-value = expression
  as? = sequence-type
  visibility? = "public" | "private" | "final" | "abstract"
  streamable? = "yes" | "no" >
  <!-- Content: xsl:accumulator-rule+ -->
</xsl:accumulator>

<xsl:accumulator-rule
  match = pattern
  phase? = "start" | "end"
  new-value = expression />

An xsl:accumulator element is a declaration of an accumulator. The name attribute defines the name of the accumulator. The value of the name attribute is an EQName, which is expanded as described in 5.1 Qualified Names.

An xsl:accumulator declaration can only appear as a top-level element in a stylesheet module.

The functions accumulator-before and accumulator-after return, respectively, the value of the accumulator before visiting the descendants of a given node, and the value after visiting the descendants of a node. Each of these functions takes a single argument, the name of the accumulator, and the function applies implicitly to the context node. The type of the return value (for both functions) is determined by the as attribute of the xsl:accumulator element.

[Definition: The functions accumulator-before and accumulator-after are referred to as the accumulator functions.]

When streaming, these functions can only be called in specific circumstances: specifically, when the context item is the node at the current position in the streamed document. This condition cannot always be detected statically. Unlike most of the rules for streamability, therefore, the use of accumulators gives rise to the possibility of dynamic errors if stylesheet code does not follow the rules for streaming.

The initial value of the accumulator is obtained by evaluating the expression in the initial-value attribute. The values for individual nodes in a tree are obtained by applying the rules contained within the xsl:accumulator declaration, as described in subsequent sections.

The expression in the initial-value attribute is evaluated with the same static and dynamic context as the expression in the select attribute of a global variable declaration.

The expression in the new-value attribute of xsl:accumulator-rule is evaluated with a static context that follows the normal rules for expressions in stylesheets, except that:

  • An additional variable is present in the context. The name of this variable is value (in no namespace), and its type is the type that appears in the as attribute of the xsl:accumulator declaration.

  • The context item for evaluation of the expression will always be a node that matches the pattern in the match attribute.

The result of both the initial-value and new-value expressions is converted to the type declared in the as attribute by applying the function conversion rules. A type error occurs if conversion is not possible. The as attribute defaults to item()*.

The effect of the streamable attribute is defined in 18.2.7 Streamability of Accumulators.

18.2.2 Informal Model for Accumulators

Informally, an accumulator is evaluated by traversing a document in tree-walking order. Each node is visited twice, once before processing its descendants, and once after processing its descendants. For consistency, this applies even to leaf nodes: each is visited twice. Attribute and namespace nodes, however, are not visited.

Before the traversal starts, a variable (called the accumulator variable) is initialized to the value of the expression given as the initial-value attribute.

On each node visit, the xsl:accumulator-rule elements are examined to see if there is a matching rule. For a match to occur, the pattern in the match attribute must match the node, and the phase attribute must be start if this is the first visit, and end if it is the second visit. If there is a matching rule, then a new value is computed for the accumulator variable using the expression contained in that rule's new-value attribute. If there is more than one matching rule, the last in document order is used. If there is no matching rule, the value of the accumulator variable does not change.

Each node is labeled with a pre-descent value for the accumulator, which is the value of the accumulator variable immediately after processing the first visit to that node, and with a post-descent value for the accumulator, which is the value of the accumulator variable immediately before processing the second visit.

The function accumulator-before delivers the pre-descent value of the accumulator at the context node; the function accumulator-after delivers the post-descent value of the accumulator at the context node.

Although this description is expressed in procedural terms, it can be seen that the two values of the accumulator for any given node depend only on the node and its preceding and (in the case of the post-descent value) descendant nodes. Calculation of both values is therefore deterministic and free of side-effects; moreover, it is clear that the values can be computed during a streaming pass of a document, provided that the rules themselves use only information that is available without repositioning the input stream.

It is permitted for the new-value expression of an accumulator rule to invoke an accumulator function. The rules ensure that a rule with phase="start" can only call the accumulator-before function, and a a rule with phase="end" can only call the accumulator-after function. When such function calls exist in an accumulator rule, they impose a dependency of one accumulator on another; a dynamic error occurs if this dependency is cyclic.

18.2.3 Formal Model for Accumulators

[Definition: A traversal of a tree is a sequence of traversal events.]

[Definition: a traversal event (shortened to event in this section) is a pair comprising a phase (start or end) and a node.] It is modelled as a map with two entries: map{"phase" : p, "node" : n} where p is the string "start" or "end" and n is a node.

The traversal of a document contains two traversal events for each node in the tree, other than attribute and namespace nodes. One of these events (the "start event") has phase = "start", the other (the "end event") has phase = "end".

The order of traversal events within a traversal is such that, given any two nodes M and N with start/end events denoted by M0, M1, N0, and N1, :

  • For any node N, N0 precedes N1;

  • If M is an ancestor of N then M0 precedes N0 and N1 precedes M1;

  • If M is on the preceding axis of N then M1 precedes N0.

The accumulator defines a (private) delta function Δ. The delta function computes the value of the accumulator for one traversal event in terms of its value for the previous traversal event. The function is defined as follows:

  1. The signature of Δ is function ($value as T, $event as map(*)) as T, where T is the sequence type declared in the as attribute of the accumulator declaration;

  2. The implementation of the function is equivalent to the following algorithm:

    1. Let R be the set of xsl:accumulator-rule elements among the children of the accumulator declaration whose phase attribute equals $event("phase") and whose match attribute is a pattern that matches $event("node")

    2. If R is empty, return $value

    3. Let Q be the xsl:accumulator-rule in R that is last in document order

    4. Return the value of the expression in the next-value attribute of Q, evaluating the expression with a singleton focus set to $event("node") and with a dynamic context that binds the variable whose name is the accumulator name to the value $value

For every node N, other than attribute and namespace nodes, the accumulator defines a pre-descent value B(N) and a post-descent value A(N) whose values are as follows:

  1. Let T be the traversal of the tree rooted at fn:root(N)

  2. Let SB be the subsequence of T starting at the first event in T and ending with the start event for node N (that is, the event map{ "phase":"start", "node":N })

  3. Let SA be the subsequence of T starting at the first event in T, and ending with the event that immediately precedes the end event for node N (that is, the event map{ "phase":"end", "node":N })

  4. Let Z be the result of evaluating the expression contained in the initial-value attribute of the xsl:accumulator declaration, using the same context as is used for evaluating global variables

  5. Then the pre-descent value B(N) is the value of fn:fold-left(SB, Z, Δ), and the post-descent value A(N) is the value of fn:fold-left(SA, Z, Δ)

18.2.4 fn:accumulator-before

Summary

Returns the pre-descent value of the selected accumulator at the context node

Signature

accumulator-before($name as xs:string) as item()*
Properties

This function is deterministicFO30, context-dependentFO30, and focus-dependentFO30.

Rules

The $name argument specifies the name of the accumulator. The value of the argument must be a string containing an EQName. If it is a lexical QName, then it is expanded as described in 5.1 Qualified Names (no prefix means no namespace).

The function returns the pre-descent value B(N)of the selected accumulator where N is the context node, as defined in 18.2.3 Formal Model for Accumulators

Error Conditions

[ERR XTDE3340] It is a dynamic error if the value is not a valid EQName, or if there is no namespace declaration in scope for the prefix of the QName, or if the name obtained by expanding the QName is not the same as the expanded name of any xsl:accumulator declaration visible in the package in which the function call appears. If the processor is able to detect the error statically (for example, when the argument is supplied as a string literal), then the processor may optionally signal this as a static error.

[ERR XTDE3350] It is a dynamic error to call the accumulator-before or accumulator-after function when there is no context item.

[ERR XTTE3360] It is a type error to call the accumulator-before or accumulator-after function when the context item is not a node, or when it is an attribute or namespace node.

[ERR XTDE3370] It is a dynamic error if the accumulator-before or accumulator-after function is called and (a) the accumulator has the property streamable="no", and (b) the context item is a node in a streamed document.

[ERR XTDE3380] If the accumulator is declared with the attribute streamable="yes" then it is a dynamic error if the accumulator-before or accumulator-after function is called unless the evaluation is performed in the course of the evaluation of either (a) the sequence constructor contained in a template rule invoked in a mode declared with streamable="yes", or (b) the sequence constructor contained in an xsl:stream instruction, or both. Call the nearest such construct in the chain of causation the controlling sequence constructor.

[ERR XTDE3390] If the accumulator is declared with the attribute streamable="yes" then it is a dynamic error if the accumulator-before or accumulator-after function is called unless the context item at the point of evaluating this function is the same node as the context item for the evaluation of the controlling sequence constructor.

[ERR XTDE3400] It is a dynamic error if the accumulator-before or accumulator-after function for an accumulator A is evaluated in the course of evaluating the new-value expression of any accumulator rule for the same accumulator A.

[ERR XTDE3410] If the accumulator is declared with the attribute streamable="yes" then it is a dynamic error if the accumulator-before function is called unless the evaluation is performed in the course of the evaluation of a pre-descent instruction within the controlling sequence constructor.

Examples

Given the accumulator:

<xsl:accumulator name="a" initial-value="1">
   <xsl:accumulator-rule match="section" new-value="$value + 1"/>
</xsl:accumulator>

and the template rule:

<xsl:template match="section">
   <xsl:value-of select="accumulator-before('a')"/>
   <xsl:apply-templates/>
</xsl:template>

The stylesheet will precede the output from processing each section with a section number that runs sequentially 1, 2, 3... irrespective of the nesting of sections.

18.2.5 fn:accumulator-after

Summary

Returns the post-descent value of the selected accumulator at the context node.

Signature

accumulator-after($name as xs:string) as item()*
Properties

This function is deterministicFO30, context-dependentFO30, and focus-dependentFO30.

Rules

The $name argument specifies the name of the accumulator. The value of the argument must be a string containing an EQName. If it is a lexical QName, then it is expanded as described in 5.1 Qualified Names (no prefix means no namespace).

The function returns the post-descent value A(N) of the selected accumulator where N is the context node, as defined in 18.2.3 Formal Model for Accumulators

Error Conditions

The following errors apply: [see ERR XTDE3340], [see ERR XTDE3350], [see ERR XTTE3360], [see ERR XTDE3370], [see ERR XTDE3380], [see ERR XTDE3390], [see ERR XTDE3400].

[ERR XTDE3420] If the accumulator is declared with the attribute streamable="yes" then it is a dynamic error if the accumulator-after function is called unless the evaluation is performed in the course of the evaluation of a post-descent instruction within the controlling sequence constructor.

Examples

Given the accumulator:

<xsl:accumulator name="w" initial-value="1">
   <xsl:accumulator-rule match="text()" 
                         new-value="$value + count(tokenize(., '\s+'))"/>
</xsl:accumulator>

and the template rule:

<xsl:template match="section">
   <xsl:apply-templates/>
   (words: <xsl:value-of select="accumulator-after('w')"/>)
</xsl:template>

The stylesheet will output at the end of each section a count of the number of words in the document up to that point, irrespective of the nesting of sections.

18.2.6 Visibility and Overriding of Accumulators

If a stylesheet contains more than one xsl:accumulator declaration with a particular name, then the one with the highest import precedence is used.

[ERR XTSE3350] It is a static error for a package to contain two or more non-hidden accumulators with the same expanded QName and the same import precedence, unless there is another accumulator with the same expanded QName, and a higher import precedence.

[ERR XTSE3360] It is a static error for a package to contain a non-hidden accumulator if either the pre-descent or post-descent functions have the same name as a non-hidden stylesheet function in the same package.

18.2.7 Streamability of Accumulators

An accumulator is guaranteed-streamable if it satisfies both the following conditions:

  1. In every contained xsl:accumulator-rule, the pattern in the match attribute is a motionless pattern.

  2. The expression in the new-value attribute is a motionless expression.

Specifying streamable="yes" on an xsl:accumulator element declares an intent that the accumulator should be guaranteed streamable according to these criteria. The consequences of declaring the accumulator to be streamable when it is not in fact guaranteed streamable depend on the conformance level of the processor, and are explained in 19.10 Streamability Guarantees.

When an accumulator is declared to be streamable, the stylesheet author must ensure that the accumulator functions are only called at appropriate points in the processing, otherwise (if streaming is actually in use) a dynamic error will occur. The rules are given below.

The pre-descent accumulator function accumulator-before can only be invoked in the course of evaluating a pre-descent instruction in a template rule that matches the context item, and the post-descent accumulator function accumulator-after can only be invoked in the course of evaluating a post-descent instruction in such a template rule. The concepts "pre-descent instruction" and "post-descent instruction" are defined in 19.8.3 Classifying Sequence Constructors.

To formalize this it is necessary to establish what it means for one construct to be evaluated in the course of evaluating another. The rules are as follows. A construct A is evaluated in the course of evaluating another construct B if any of the following conditions applies:

  • A is an operand of B (this does not include the body of an inline function declaration)

  • A is the body of a function (either an inline function declaration or a stylesheet function called by a function call B

  • A is the body of a named template called by an xsl:call-template instruction B

  • A is the body of an attribute set invoked by an instruction B containing an [xsl:]use-attribute-set attribute

  • A is the body of a template rule called by an xsl:apply-templates, xsl:apply-imports, or xsl:next-match instruction B

  • A is the new-value expression of an accumulator rule that matches a node N, and B is a consuming instruction evaluated with N as its context item

  • There is a construct M such that A is evaluated in the course of evaluating M, and M is evaluated in the course of evaluating B.

Note:

The initializer of a variable is NOT evaluated in the course of evaluating a variable reference.

An xsl:variable instruction and its select attribute or contained sequence constructor ARE evaluated in the course of evaluating the sequence constructor that contains the xsl:variable instruction. Where a variable is bound to the result of an accumulator function, or a value computed from such a result, the position of the xsl:variable instruction within its sequence constructor may be significant, insofar as its position relative to a consuming instruction makes it a pre-descent or post-descent instruction.

If a call on accumulator-before or accumulator-after is evaluated for a streamable accumulator then:

  1. The evaluation must occur in the course of evaluating a pre-descent or post-descent instruction in some streamed template rule T, respectively

  2. The context item at the point of invocation of the accumulator function must be the same as the context node for T.

18.2.8 Examples of Accumulators

Example: Remember the Title of a Document

Consider an XHTML document in which the title of the document is represented by the content of the first title element appearing as a child of the head element, which in turn appears as a child of the html element. Suppose that we want to process the document in streaming mode, and that we want to avoid outputting the content of the h1 element if it is the same as the document title.

This can be achieved by remembering the value of the title in an accumulator variable.

  <xsl:accumulator name="firstTitle" as="xs:string?" initial-value="()">
    <xsl:accumulator-rule match="html/head/title[1]" new-value="string(.)"/>
  </xsl:accumulator>
  

Subsequently, while processing an h1 element appearing later in the document, the value can be referenced:

  <xsl:template match="h1">
    <xsl:variable name="firstTitle" select="accumulator-before('firstTitle')"/>
    <xsl:variable name="thisTitle" select="string(.)"/>
    <xsl:if test="$thisTitle ne $firstTitle">
      <div class="heading-1"><xsl:value-of select="$thisTitle"/></div>
    </xsl:if>
    </xsl:template>

Note:

This example illustrates that the order of the variable declarations within a sequence constructor is significant, even when there is no direct dependency of one variable on another.

 

Example: Keep a Word Count

Suppose that there is a requirement to output, at the end of the HTML rendition of a document, a paragraph giving the total number of words in the document.

An accumulator can be used to maintain the word count:

  <xsl:accumulator name="word-count" 
                   as="xs:integer" 
                   initial-value="0">
    <xsl:accumulator-rule match="text()" 
         new-value="$value + count(tokenize(string(.), '\W+'))"/>
  </xsl:accumulator>
  

The final value can be output at the end of the document:

   <xsl:template match="/">
     <xsl:apply-templates/>
     <p>Word count: <xsl:value-of select="accumulator-after('word-count')"/></p>
   </xsl:template>

 

Example: Output Hierarchic Section Numbers

Consider a document in which section elements are nested within section elements to arbitrary depth, and there is a requirement to render the document with hierarchic section numbers of the form 3.5.1.4.

The current section number can be maintained in an accumulator in the form of a sequence of integers, managed as a stack. The number of integers represents the current level of nesting, and the value of each integer represents the number of preceding sibling sections encountered at that level. For convenience the first item in the sequence represents the top of thenstack.

<xsl:accumulator name="section-nr" as="xs:integer*" 
                 initial-value="0">
  <xsl:accumulator-rule match="section" phase="start" 
                 new-value="0, head($value)+1, tail($value)"/>
  <xsl:accumulator-rule match="section" phase="end" 
                 new-value="tail($value) (:pop:)"/>
</xsl:accumulator>  

To illustrate this, consider the values after processing a series of start and end tags:

events accumulator value required section number
<section> 0, 1 1
<section> 0, 1, 1 1.1
</section> 1, 1
<section> 0, 2, 1 1.2
</section> 2, 1
<section> 0, 3, 1 1.3
<section> 0, 1, 3, 1 1.3.1
</section> 1, 3, 1
<section> 0, 2, 3, 1 1.3.2
</section> 2, 3, 1
</section> 3, 1
</section> 1

The section number for a section can thus be generated as:

<xsl:template match="section">
  <p>
    <xsl:value-of select="reverse(tail(accumulator('section-nr')))" 
                  separator="."/>
  </p>
  <xsl:apply-templates/>
</xsl:template>
                  

 

Example: Compute a Histogram showing the Number of Books, by Publisher
 <xsl:accumulator name="histogram" as="map(xs:string, xs:integer)"
    initial-value="map{}">
    <xsl:accumulator-rule match="book" new-value=""
       if (map:contains($value, @publisher)) 
       then map:put($value, @publisher, 
                            accumulator-before('histogram')(@publisher)+1)
       else map:put($value, @publisher, 
                            1)"/>
 </xsl:accumulator>

The new-value expression is evaluated with the variable $value set to the current value, and with the context node as the node being visited.

18.3 fn:copy-of

Summary

Returns a deep copy of the node supplied as the $node argument, or of the context node if the argument is absent.

Signatures

copy-of() as node()
copy-of($nodes as node()*) as node()*
Properties

The zero-argument form of this function is nondeterministicFO30, focus-dependentFO30, and context-independentFO30.

The one-argument form of this function is nondeterministicFO30, focus-independentFO30, and context-independentFO30.

Rules

The zero-argument form of this function has the same effect as calling copy-of(.), that is, supplying the context item as an implicit argument.

The function returns a deep copy of the node sequence supplied as the argument $nodes. If the argument is an empty sequence, the function returns an empty sequence. The effect is the same as that of the function:

<xsl:function name="fn:copy-of" as="node()*" 
              identity-sensitive="no">
  <xsl:param name="nodes" as="node()*/>
  <xsl:copy-of select="$nodes" 
               copy-namespaces="yes" 
               validation="preserve"/>
</xsl:function>

The streamability analysis, however, is different: see 19.8.8 Classifying Calls to Built-In Functions.

If the function is called more than once with the same argument, it is implementation-dependent whether each call returns the same node, or whether multiple calls return different nodes. That is, in the case where $X is a single node, the result of the expression copy-of($X) is copy-of($X) is implementation-dependent. However, copy-of($X) is $X will always be false.

Notes

The copy-of function is available for use (and is primarily intended for use) when a source document is processed using streaming. It can also be used when not streaming. The effect is to take a copy of the subtree rooted at the current node, and to make this available as a normal tree, that can be processed without any of the restrictions that apply while streaming, for example only being able to process children once. The copy, of course, does not include siblings or ancestors of the context node, so any attempt to navigate to siblings or ancestors will result in an empty sequence being returned.

Examples

Using copy-of() while streaming:

This example copies from the source document all employees who work in marketing and are based in Dubai. Because there are two accesses using the child axis, it is not possible to do this without buffering each employee in memory, which can be achieved using the copy-of function.

<xsl:stream href="employees.xml">
  <xsl:sequence select="copy-of(employees/employee)
                          [department='Marketing' and location='Dubai']"/>
</xsl:stream>

18.4 fn:snapshot

Summary

Returns a copy of a node together with its ancestors and descendants and their attributes and namespaces.

Signatures

snapshot() as node()
snapshot($nodes as node()*) as node()*
Properties

The zero-argument form of this function is nondeterministicFO30, focus-dependentFO30, and context-independentFO30.

The one-argument form of this function is nondeterministicFO30, focus-independentFO30, and context-independentFO30.

Rules

The zero-argument form of this function has the same effect as calling snapshot(.), that is, supplying the context item as an implicit argument.

The function returns a seequence of nodes in which each node is a snapshot of the corresponding node in the input sequence supplied as the argument $node. If the argument is an empty sequence, the function returns an empty sequence.

If the function is called more than once with the same argument, it is implementation-dependent whether each call returns the same node, or whether multiple calls return different nodes. That is, the result of the expression snapshot($X) is snapshot($X) is implementation-dependent.

[Definition: A snapshot of a node N is a deep copy of N, as produced by the xsl:copy-of instruction with copy-namespaces set to yes and validation set to preserve, with the additional property that for every ancestor of N, the copy also has a corresponding ancestor whose name, node-kind, and base URI are the same as the corresponding ancestor of N, and that has copies of the attributes and namespaces of the corresponding ancestor of N. But the ancestor has a type annotation of xs:anyType, has the properties nilled, is-id, and is-idref set to false, and has no children other than the child that is a copy of N or one of its ancestors.]

More formally, a snapshot of a node is the result of the following function.

<xsl:function name="fn:snapshot" as="node()?" identity-sensitive="no">
  <xsl:param name="nodes" as="node()*"/>
  
  <!-- create a copy of the tree containing the supplied node, retaining 
       * only the supplied node, its attributes and namespaces
       * the ancestors of the supplied node, 
       * their attributes and namespaces;
       * the descendants of the supplied node, 
       * their attributes and namespaces;
       -->
  <xsl:for-each select="$nodes">
    <xsl:variable name="origin" select="."/>
    <xsl:variable name="root-copy" as="node()">
      <xsl:apply-templates select="root($origin)" mode="snapshot">
        <xsl:with-param name="origin" select="$origin" tunnel="yes"/>
      </xsl:apply-templates>
    </xsl:variable>
  
    <!-- find and return the node in the copied tree 
         that corresponds to the origin node
       --> 
    <xsl:sequence select="
         $root-copy/descendant-or-self::node()/(.|@*|namespace::*)
                              [f:corresponds(., $origin)]"/>
  </xsl:for-each>    
</xsl:function>

<xsl:template match="." mode="snapshot">
  <xsl:param name="origin" as="node()" tunnel="yes"/>
  <xsl:choose>
    <xsl:when test=". is $origin">
      <xsl:copy-of select="." validation="preserve"/>
    </xsl:when>
    <xsl:when test=". intersect $origin/ancestor::node()">
      <xsl:copy validation="strip">
        <xsl:copy-of select="@*" validation="preserve"/>
        <xsl:apply-templates mode="snapshot"/>
      </xsl:copy>
    </xsl:when>
    <xsl:otherwise/>
  </xsl:choose>
</xsl:template>

<!-- f:corresponds compares two nodes and returns true if all 
       the following are true:
     * they are at the same depth in their respective trees
     * they have the same name (or none)
     * they have the same node kind
     The tests on node name and node kind are needed only when 
     the origin node is an attribute or namespace.
     -->
<xsl:function name="f:corresponds" as="xs:boolean">
  <xsl:param name="node1" as="node()"/>
  <xsl:param name="node2" as="node()"/>
  <xsl:sequence select="
    count($node1/ancestor::node()) = count($node2/ancestor::node()) and
    deep-equal(node-name($node1), node-name($node2)) and
    f:node-kind($node1) = f:node-kind($node2)"/>    
</xsl:function>

<!-- f:node-kind returns the node kind of a node as a string
     -->
<xsl:function name="f:node-kind" as="xs:string">
  <xsl:param name="node" as="node()"/>
  <xsl:choose>
    <xsl:when test="$node instance of document-node()">D</xsl:when>
    <xsl:when test="$node instance of element(*)">E</xsl:when>
    <xsl:when test="$node instance of attribute(*)">A</xsl:when>
    <xsl:when test="$node instance of text()">T</xsl:when>
    <xsl:when test="$node instance of comment()">C</xsl:when>
    <xsl:when test="$node instance of 
                          processing-instruction()">P</xsl:when>
    <xsl:when test="$node instance of namespace-node()">N</xsl:when>
  </xsl:choose>
</xsl:function>
 
Notes

The snapshot function is available for use (and is primarily intended for use) when a source document is processed using streaming. It can also be used when not streaming. The effect is to take a copy of the subtree rooted at the current node, along with copies of the ancestors and their attributes, and to make this available as a normal tree, that can be processed without any of the restrictions that apply while streaming, for example only being able to process children once. The copy, of course, does not include siblings of the context node or of its ancestors, so any attempt to navigate to these siblings will result in an empty sequence being returned.

Examples

Using snapshot() while streaming:

This example copies from the source document all employees who work in marketing and are based in Dubai. It assumes that employees are grouped by location. Because there are two accesses using the child axis (referencing department and salary), it is not possible to do this without buffering each employee in memory. The snapshot function is used in preference to the simpler copy-of so that access to attributes of the parent location element remains possible.

<xsl:stream href="employees.xml">
  <xsl:for-each select="snapshot(locations/location[@name='Dubai']
                          /employee)[department='Marketing']">
    <employee>
      <location code="{../@code}"/>
      <salary value="{salary}"/>
    </employee>
  </xsl:for-each>
</xsl:stream>

19 Streamability

This section describes the analysis that determines whether constructs in the stylesheet are streamable. More precisely, the analysis determines properties of constructs such as template rules, and the values of these properties determine whether constructs are guaranteed-streamable, which in turn (see 19.10 Streamability Guarantees) imposes rules on how the constructs are handled by processors that implement the streaming feature. The analysis has no effect on the behavior of processors that do not implement this feature.

The analysis is relevant to constructs such as streamable template rules and the xsl:stream instruction that process a single streamed input document. The xsl:merge instruction, which processes multiple streamed inputs, has its own rules.

The rules in this section operate on the expression tree (more properly, construct tree) that is typically output by the XSLT and XPath parser. For the most part, the rules depend only on identifying the syntactic constructs that are present.

The rules in this section generally consider each component in the stylesheet (and in the case of template rules, each template rule) in isolation. The exception is that where a component contains references to other components (such as global variables, functions, or named templates), then information from the signature of the referenced component is sometimes used. This is invariably information that cannot be changed if a component is overridden in a different package. The analysis thus requires as a pre-condition that function calls and calls on named templates have been resolved to the extent that the corresponding function/template signature is known. It also requires that variable references referring to grouping variables (those declared in a bind-XXX attribute of an xsl:for-each-group, xsl:merge, or xsl:merge-source element) have been identified as such.

The detailed way in which the construct tree is derived from the lexical form of the stylesheet is not described in this specification. There are many ways in which the tree can be optimized without affecting the result of the rules in this section: for example, a sequence constructor containing a single instruction can be replaced by that instructon, and a parenthesized expression can be replaced by its content.

[Definition: The term construct refers to the union of the following: a sequence constructor, an instruction, an attribute set, a value template, an expression, or a pattern.]

These constructs are classified into construct kinds: in particular, instructions are classified according to the name of the XSLT instruction, and expressions are classified according to the most specific production in the XPath grammar that the expression satisfies. (This means, for example, that 2+2 is classified as an AdditiveExpr, rather than say as a UnionExpr; although it also satisfies the production rule for UnionExpr, AdditiveExpr is more specific.)

[Definition: For every construct kind, there is a set of zero or more operand roles.] For example, an AdditiveExpr has two operand roles, referred to as the left-hand operand and the right-hand operand, while an IfExpr has three, referred to as the condition, the then-clause, and the else-clause. A function call with three arguments has three operand roles, called the first, second, and third arguments. The names of the operand roles for each construct kind are not formally listed, but should be clear from the context.

[Definition: In an actual instance of a construct, there will be a number of operands.] Each operand is itself a construct; the construct tree can be defined as the transitive relation between constructs and their operands. Each operand is associated with exactly one of the operand roles for the construct type. There may be operand roles where the operand is optional (for example, the separator attribute of the xsl:value-of instruction), and there may be operand roles that can be occupied by multiple operands (for example, the xsl:when/@test condition in xsl:choose, or the arguments of the concatFO30 function).

Operand roles have a number of properties used in the analysis:

[Definition: For some construct kinds, one or more operand roles may be defined to form a choice operand group. This concept is used where it is known that operands are mutually exclusive (for example the then and else clauses in a conditional expression).]

[Definition: The combined posture of a choice operand group is determined by the postures of the operands in the group, and is the first of the following that applies:]

  1. If any of the input postures is roaming, then the combined posture is roaming.

  2. If all of the input postures are grounded, then the combined posture is grounded.

  3. If one or more of the input postures is climbing and the remainder (if any) are grounded, then the combined posture is climbing.

  4. If one or more of the input postures is striding and the remainder (if any) are grounded, then the combined posture is striding.

  5. If one or more of the input postures is crawling and the remainder (if any) are either striding or grounded, then the combined posture is crawling.

  6. Otherwise (for example, if the group includes both an operand with climbing posture and one with crawling posture), the combined posture is roaming.

[Definition: The type-determined usage of an operand is as follows: if the required type (ignoring occurrence indicator) is function(*) or a subtype thereof, then inspection; if the required type (ignoring occurrence indicator) is xs:anyAtomicType or a subtype thereof, then absorption; otherwise navigation.]

The process of determining whether a construct is streamable reduces to determining properties of the constructs in the construct tree. The properties in question (which are described in greater detail in subsequent sections) are:

  1. The static type of the construct. When the construct is evaluated, its value will always be an instance of this type. The value is an ItemTypeXP30; although type inferencing is capable of determining information about the cardinality as well as the item type, the streamability analysis makes no use of this.

  2. The context item type: that is, the static type of the context item potentially used as input to the construct. When the construct is evaluated, the context item used to evaluate the construct (if it is used at all) will be an instance of this type.

  3. [Definition: The posture of the expression. This captures information about the way in which the streamed input document is positioned on return from evaluating the construct. The posture takes one of the values climbing, striding, crawling, roaming, or grounded. ] The meanings of these terms are explained in 19.5 Determining the Posture of a Construct.

  4. [Definition: The context posture. This captures information about how the context item used as input to the construct is positioned relative to the streamed input. The context posture of a construct C is the posture of the expression whose value sets the focus for the evaluation of C.]. Rules for determining the context posture of any construct are given in 19.6 Determining the Context Posture.

  5. The sweep of the construct. The sweep of a construct gives information about whether and how the evaluation of the construct changes the current position in a streamed input document. The possible values are motionless, consuming, and free-ranging. These terms are explained in 19.7 The Sweep of a Construct.

The values of these properties for a top-level construct such as the body of a template rule determine whether the construct is streamable.

The values of these properties are not independent. For example, if the static type is atomic, then the posture will always be grounded; if the sweep is free-ranging, then the posture will always be roaming.

The posture and sweep of a construct, as defined above, are calculated in relation to a particular streamed input document. If there is more than one streamed input document, then a construct that is motionless with respect to one streamed input might be consuming with respect to another. In practice, though, the streamability analysis is only ever concerned with one particular streamed input at a time; constructs are analyzed in relation to the innermost containing xsl:template, xsl:stream, xsl:accumulator, or xsl:merge-source element, and this container implicitly defines the streamed input document that is relevant. The streamed input document affecting a construct is always the document that contains the context item for evaluation of that construct, with one exception: a variable reference to a variable bound in the bind-group attribute of xsl:for-each-group or the bind-source attribute of an xsl:merge-source element. To prevent this causing complications, there are rules constraining where such variable references may appear.

19.1 An Optimization: Pattern-Based Scanning

The rules given later in this chapter for determining streamability produce the result that the expression count(//section/head) is not streamable. The reason for this is that a naive nested loop evaluation of the path expression //section/head will not always deliver nodes in document order; this can be seen by examining the source document below, where a child of the first section appears in document order after a child of the second section:

<section>
  <section>
     <head/>
  </section>
  <head/>
</section>  

An implementation that literally followed the semantics of path expressions as defined in [XPath 3.0] would therefore require to sort the nodes into document order, and sorting is incompatible with streaming.

There is however a viable strategy for processing this expression in a streaming manner, for example to rewrite the expression as count(/descendant::head[parent::section]).

In order to make such expressions streamable, implementations must therefore detect this situation in the construct tree and perform an appropriate rewrite before continuing with the analysis. Specifically, any PathExpr E that is the equivalent expression of some motionless pattern P is replaced by a call on a streamable function that selects the same nodes as would have been selected by E in the absence of streaming restrictions. This function call has a sweep of consuming and a posture of crawling; its static type is that of the original expression E. This makes it eligible to be used, for example, as the argument of the countFO30 function.

Note:

The function used in this rewrite needs to do more than simply test all descendant nodes to see if they match the pattern; for example if the expression is p//q then it must also check that the relevant p element is indeed a child of the original context item.

This rewrite will not always succeed in making the construct streamable. For example <xsl:value-of select="//head"/> will still fail the streamability tests, because of the possibility that one head element is a child of another. This problem can be remedied by writing <xsl:value-of select="//head/text()"/>.

It should also be noted that not all downward path expressions are equivalent to motionless patterns; an example is a[2]. Positional predicates are allowed in streamable path expressions, but not in motionless patterns.

In practice, of course, processors may use a different algorithm if it achieves the same effect.

19.2 Determining the Static Type of a Construct

The static type of an construct is such that all values produced by evaluating the construct will conform to that type.

Although all constructs have a static type, the streamability analysis only needs to know the static type of XPath expressions, so the rules here are confined to that case. In addition, the analysis only needs to know the item type, and not the cardinality. For constructs other than expressions, the static type for the purpose of streamability analysis is taken as item().

The rules given here are deliberately simple. Implementations may well be able to compute a more precise static type, but this will rarely be useful for streamability analysis. The item type for each kind of XPath expression is determined by the rules below. In the first column, numbers in square brackets are production numbers from the XPath 3.0 specification. In the second column, the Proforma uses an informal notation used both to provide a reminder of the syntax of the construct in question, and to attach labels to its operand roles so that they can be referred to in the text of the third column.

Construct Proforma Static Item Type
Expr [6] A,B the least common supertype of A and B
ForExpr [8] for $x in S return A the item type of A
LetExpr [11] let $x := S the item type of S
QuantifiedExpr [14] some|every $x in S satisfies C xs:boolean
IfExpr [15] if (C) then T else E the least common supertype of T and E
OrExpr [16] A or B xs:boolean
AndExpr [17] A and B xs:boolean
ComparisonExpr [18] A = B, A eq B, A is B xs:boolean
StringConcatExpr [19] A || B xs:string
RangeExpr [20] A to B xs:integer
AdditiveExpr [21] A + B xs:anyAtomicType
MultiplicativeExpr [22] A * B xs:anyAtomicType
UnionExpr [23] A | B the least common supertype of A and B
IntersectExceptExpr [24] A intersect B, A except B the type of A
InstanceOfExpr [25] A instance of T xs:boolean
TreatExpr [26] A treat as T the item type of T
CastableExpr [27] A castable as T xs:boolean
CastExpr [28] A cast as T the type T
UnaryExpr [29] -N numeric
SimpleMapExpr [34] A ! B the type of B
PathExpr [35] / document-node()
/P the type of P
//P the type of P
RelativePathExpr [36] A/B, A//B the type of B
AxisStep [36] A[P] the type of A
ForwardStep [39] , ReverseStep [42] Axis::NodeTest If the NodeTest is a KindTest K, then K (for example, element() or comment()). Otherwise (the NodeTest is a NameTest), the type corresponding to the principal node kind of the axis, for example element() or attribute().
PostfixExpr [48] Filter Expression A[B] the type of A
Dynamic Function Call A(B, C) the return type of the function type of A
Literal [53] "pH", 93.7 xs:string, xs:integer, xs:decimal, or xs:double, depending on the form of the literal
VarRef [55] $V For a variable declared using xsl:variable or xsl:param, and for parameters of inline function expressions: the declared type of the variable, defaulting to item(). For variables declared using for, let, some, and every expressions: the item type of the expression to which the variable is bound. For the binding variables of xsl:for-each-group: the type of the relevant expression in the xsl:for-each-group instruction (select, group-by, or group-adjacent)
ParenthesizedExpr [57] (E) the type of E
() xs:error (a type that has no instances)
ContextItemExpr [58] . the context item type: see below
FunctionCall [59] F(X, Y) the declared result type of function F
NamedFunctionRef [63] F#n the declared function type of the referenced function F
InlineFunctionExpr [64] function(P) {E} the declared type of the anonymous inline function
MapExpr [202] map{"A":E, "B":F} map(*)

In some cases the above entries require computation of the least common type of two types T and U. Since item types form a lattice rather than a hierarchy, there may be a set of types V such that T and U are both subtypes of every type in V, and no type in V is unambiguously the "least" common type in the sense that all the others are subtypes of it. In this situation the choice of which type in V to use as the inferred static type is implementation-defined.

Note:

The streamability analysis in this chapter is not schema-aware. There are cases where use of schema type information might enable a processor to determine that a construct is streamable when it would be unable to make this determination otherwise. Two examples:

  • A processor might decide that a construct such as price + salesTax is streamable if both the child elements have a simple type such as xs:decimal, or if the order in which they appear in the input document is known.

  • A processor might decide that a step using the descendant axis, such as .//title, has striding rather than crawling posture if it can establish that two title elements will never overlap (that is, a title cannot contain another title). This would allow the instruction <xsl:apply-templates select=".//title"/> to be used in a streaming template rule.

Although such constructs are not guaranteed streamable according to this specification, there is nothing to prevent a processor providing a streamed implementation if it is able to do so.

19.3 Determining the Context Item Type

[Definition: For every expression, it is possible to establish by static analysis, information about the item type of the context item for evaluation of that expression. This is called the context item type of the expression.]

The semantics of every construct, defined in this specification or in the XPath specification, describe how the focus for evaluating each operand of the construct is determined. In most cases the focus is the same as that of the parent construct. In some cases the focus is determined by evaluating some other expression, for example in the expressions A/B, A!B, or A[B], the focus for evaluating B is A. More generally:

  • [Definition: A focus-changing construct is a construct that has one or more operands that are evaluated with a different focus from the parent construct.]

    Note:

    Examples of focus-changing constructs include the instructions xsl:for-each, xsl:iterate, and xsl:for-each-group; path expressions, filter expressions, and simple mapping expressions; and all patterns.

  • [Definition: Within a focus-changing construct there is in many cases one operand whose value determines the focus for evaluating other operands; this is referred to as the controlling operand.]

    Note:

    For example, the controlling operand of a xsl:for-each, xsl:iterate, or xsl:for-each-group instruction is the expression in its select attribute; the controlling operand of a filter expression E[P] is E, and the controlling operand of a simple mapping expression A!B is A.

  • [Definition: Within a focus-changing construct there are one or more operands that are evaluated with a focus determined by the controlling operand (or in some cases such as xsl:on-completion, with an absent focus); these are referred to as controlled operands.]

    Note:

    For example, the main controlled operand of a xsl:for-each, xsl:iterate, or xsl:for-each-group instruction is the contained sequence constructor; the controlled operand of a filter expression E[P] is P, and the controlled operand of a simple mapping expression A!B is B.

  • [Definition: The focus-setting container of a construct C is the innermost focus-changing construct F (if one exists) such that C is directly or indirectly contained in a controlled operand of F. If there is no such construct F, then the focus-setting container is the containing declaration, for example an xsl:function or xsl:template element.]

    Note:

    For example, if an instruction appears as a child of xsl:for-each, then its focus-setting container is the xsl:for-each instruction; if an expression appears within the predicate of a filter expression, its focus-setting container is the filter expression.

The context item type of a construct C is the first of the following that applies:

  1. If the focus-setting container of C is an xsl:function element, an inline function declaration, or an xsl:on-completion element, then the context item type is xs:error.

    Note:

    This is essentially an error case; expressions that depend on the focus should not normally appear within a construct that sets the focus to absent.

  2. If the focus-setting container of C is an xsl:stream instruction, then the context item type is document-node().

  3. If the focus-setting container of C is a template rule, then the context item type is the match type of the match pattern of the template rule, defined below.

  4. If the focus-setting container of C is a PredicatePattern, then the context item type is item().

  5. If the focus-setting container is any other declaration, for example a global variable declaration, the context item type is item().

  6. Otherwise, the context item type is the statically-inferred type (see 19.2 Determining the Static Type of a Construct) of the controlling operand of the focus-setting container of C.

[Definition: The match type of a pattern is the most specific ItemType that is known to match all items that the pattern can match.] The match type of a pattern is the statically-inferred item type of the pattern's equivalent expression, determined according to the rules in 19.2 Determining the Static Type of a Construct. For example, the match type of the pattern para[1] is element(), while that of the pattern @code[.='x'] is attribute()

19.4 Operand Roles

An operand role gives information about the operands of a particular kind of construct. The two important properties of an operand role are the required type and the operand usage.

The usage of an operand role is relevant only when the value of an operand supplied in that role is a node, or a sequence that contains nodes. It is one of the following:

  • [Definition: An operand usage of absorption indicates that the construct reads the subtree(s) rooted at a supplied node(s).] Examples are constructs that atomize their operands, or that obtain the string value of a supplied node, or that copy the supplied node to a new tree. Another example is the deep-equalFO30 function, which compares the subtrees rooted at the nodes supplied in its first two arguments.

  • [Definition: An operand usage of inspection indicates that the construct accesses properties of a supplied node that are available without reading its subtree.] Examples are functions such as nameFO30 and base-uriFO30, and the instance of expression which tests the type of a node (or other item). or functions such as countFO30, existsFO30, and booleanFO30 which are only interested in the existence of the node, and not in its properties.

  • [Definition: An operand usage of transmission indicates that the construct will (potentially) return a supplied node as part of its result to the calling construct (that is, to its parent in the construct tree).] It also indicates that document order is preserved: if the input is in document order, then the result must be in document order. An example is a filter expression, where nodes in the base expression (the expression being filtered) will typically appear in the result of the filter expression, in their original order.

  • [Definition: An operand usage of navigation indicates that the construct may navigate freely from the supplied node to other nodes in the same tree, in a way that is not constrained by the streamability rules.] This covers several cases: cases where it is known that the construct performs impermissible navigation (for example, the xsl:number instruction) or reordering (the reverseFO30 function), or that require look-ahead (the innermostFO30 function) and also cases where the analysis is unable to determine what use is made of the node, for example because it is passed as an argument to a user-defined function, or retained in a variable.

The assignment of operand usages to each operand role of each kind of construct is defined in 19.8 Classifying Constructs.

19.4.1 Examples showing the Effect of Operand Usage

Example: The Effect of Operand Usage on the Streamability of a Context Item Expression

Consider the following construct:

<xsl:stream href="emps.xml">
  <xsl:for-each select="*/emp">
    <xsl:value-of select="."/>
  </xsl:for-each>
</xsl:stream>

To assess the streamability, we follow the following logic:

  1. The top-level construct is a sequence constructor. It is evaluated with a document node as the context item, and with a striding posture.

  2. The sequence constructor has one child instruction, which has an operand usage of transmission.

  3. The xsl:for-each instrunction evaluates its select expression, with the context item and posture unchanged.

  4. The step child::* is evaluated with this context item and posture. The posture transition rules permit this; we now have a sequence of child elements, and still a striding posture.

  5. The same applies to the next step, child::emp

  6. The content of the xsl:for-each instruction is a sequence constructor which itself has a single operand, the xsl:value-of instruction.

  7. The xsl:value-of instruction is evaluated once for each emp child, with that child as context item and in a striding posture. This instruction uses the general streamability rules. The operand usage of the select expression is absorption. This means that the result of the xsl:value-of instruction is grounded and consuming.

  8. The result of the trivial sequence constructor contained in the xsl:for-each instruction is therefore grounded and consuming

  9. The result of the xsl:for-each instruction (see 19.8.4.17 Streamability of xsl:for-each) is therefore grounded and consuming

  10. The result of the trivial sequence constructor contained in the xsl:stream instruction is therefore grounded and consuming

  11. The xsl:stream instruction is therefore guaranteed-streamable.

Now consider a slightly different construct:

<xsl:stream href="emps.xml">
  <xsl:for-each select="*/emp">
    <xsl:sequence select="."/>
  </xsl:for-each>
</xsl:stream>

To assess the streamability, we follow the following logic:

  1. The top-level construct is a sequence constructor. It is evaluated with a document node as the context item, and with a striding posture.

  2. The sequence constructor has one child instruction, which has an operand usage of transmission.

  3. The xsl:for-each instruction evaluates its select expression, with the context item and posture unchanged.

  4. The step child::* is evaluated with this context item and posture. The posture transition rules permit this; we now have a sequence of child elements, and still a striding posture.

  5. The same applies to the next step, child::emp

  6. The content of the xsl:for-each instruction is a sequence constructor which itself has a single operand, the xsl:sequence instruction.

  7. The xsl:sequence instruction is evaluated once for each emp child, with that child as context item and in a striding posture. This instruction uses the general streamability rules. The operand usage of the select expression is transmission. This means that the result of the xsl:sequence instruction is striding and motionless.

  8. The result of the trivial sequence constructor contained in the xsl:for-each instruction is therefore also striding and motionless.

  9. The result of the xsl:for-each instruction (see 19.8.4.17 Streamability of xsl:for-each) is therefore striding and motionless.

  10. The result of the trivial sequence constructor contained in the xsl:stream instruction is therefore striding and motionless.

  11. The xsl:stream instruction is therefore not guaranteed-streamable.

Expressed informally, the result of an xsl:stream instruction (or of a streamable template rule) must not contain streamed nodes. The reason for this is that once streamed nodes are returned to constructs that are not declared streamable and therefore have no streamability constraints, there is no way to analyze what happens to them, and thus to guarantee streamability.

 

Example: The Effect of Operand Roles on the Streamability of Path Expressions

Consider the expression .//chapter.

When this appears as an argument to the function countFO30 or existsFO30, it can be streamed (it is a consuming expression, meaning that the subtree rooted at the context item needs to be read in order to evaluate the expression). A possible strategy for performing a streamed evaluation is to read all descendants of the context item in document order, checking each one to see whether its name is chapter. The sweep of the expression will be consuming, and its posture will be crawling.

The operand usage (the usage of the argument to countFO30 or existsFO30) is defined as a inspection. The general streamability rules show that when the posture of an operand is crawling and the operand usage is inspection, the resulting expression is motionless

When the same expression appears as an argument to a call on a user-defined function, and the declared type of the relevant argument is node()*, then it is not possible to determine whether the expression is streamable or not, because the streamability analysis does not attempt to follow the data flow across functions (also, the function in question could be overridden in another package). This operand usage (where an expression returns nodes and the processor cannot determine how those nodes might be used) is defined as navigation. The expression in this context is classified as roaming and free-ranging, which effectively means that streaming is not guaranteed. Although the expression is not guaranteed streamable, some processors might do better, for example by examining what the called function does with the argument, or by allowing the stylesheet author to make assertions about the behavior of the called function using extension attributes.

When the same expression appears as an argument to the function string-joinFO30, the processor knows that it will need to access the subtree of each selected section element in order to compute the result of the function (the argument to string-joinFO30 is classified as having operand usage absorption). The processor does not know, however, whether these subtrees will be overlapping (one section might contain another). If they are overlapping, the expression will not be streamable. The analysis assumes the worst case, so it classifies the expression as free-ranging, which effectively means that streaming is not guaranteed. Some processors might do better, for example by using schema-based inferencing.

19.5 Determining the Posture of a Construct

The posture of an construct indicates the relationship of the nodes selected by the construct to a streamed input document. The value is one of the following:

  • [Definition: Grounded: indicates that the value returned by the construct does not contain nodes from the streamed input document]. Atomic values and function items are always grounded; nodes are grounded if it is known that the they are in a non-streamed document. For example the expressions doc('x') and copy-of(.) both return grounded nodes.

  • [Definition: Climbing: indicates that nodes returned by the construct are reached by navigating the parent, ancestor[-or-self], attribute, and/or namespace axes from the node at the current streaming position.] When the context posture is climbing, use of certain axes such as parent and ancestor is permitted, but use of other axes such as child or descendant violates the streamability rules.

  • [Definition: Crawling: typically indicates that nodes returned by a construct are reached by navigating the descendant[-or-self] axis.] Nodes reached in this way potentially have overlapping subtrees, so further downward navigation is not permitted. Expressions that can be statically determined to return a singleton node (for example head(.//title)) generate a result with no overlapping subtrees, so they are striding rather than crawling.

  • [Definition: Striding: indicates that the result of a construct is a sequence of nodes, in document order, that are peers in the sense that none of them is an ancestor or descendant of any other.] This is typically achieved by using one or more steps involving the child axis only. Use of the outermostFO30 function can also result in a striding posture, as can functions such as headFO30 or zero-or-oneFO30 that ensure the result will be a singleton node.

  • [Definition: Roaming: indicates that the nodes returned by an expression could be anywhere in the tree, which inevitably means that the construct cannot be evaluated using streaming.] For example, the posture of an axis step using the following or preceding axis will typically be roaming, which leads the analysis to conclude that the construct is not streamable.

Note:

One way to think about the posture values is as labels for states in a finite state automaton, where the alphabet of symbols accepted by the automaton is the set of 13 XPath axes, and the sentence being parsed is a path expression containing a sequence of axis steps. For example, use of the descendant axis when the current state is striding moves the new state to crawling, and use of the parent axis then takes it to climbing.

The posture of a construct is determined in one of several ways:

  • For axis steps, the posture of the expression is determined by the context posture and the choice of axis. For example, an axis step using the ancestor axis always has a posture of climbing, while an axis step using the child axis, if the context posture is striding, will itself have a posture of striding. The rules for the posture transitions produced by axis steps are given in 19.8.7.7 Streamability of Axis Steps.

  • For many other constructs, the posture is determined by the general streamability rules. These determine the result posture in terms of the operands to the construct and the way in which each operand is used. For example, a construct that accepts a streamed node as the value of an operand, and atomizes that node, will generally have a posture of grounded.

  • Other constructs have their own special rules, which are all listed in this chapter. For example, a call on the rootFO30 function behaves analogously to an axis step, and is described in 19.8.8.10 Streamability of the root function. Special rules are needed for:

    • Constructs that evaluate an operand more than once, such as an XPath for expression;

    • Constructs that have alternatives among their operands, such as an XPath if expression;

    • Constructs that navigate relative to the context item, such as axis steps;

    • Constructs with implicit inputs, such as the context item expression . (dot);

    • Constructs that change the focus, such as a filter expression;

    • Constructs that invoke functions or templates.

19.6 Determining the Context Posture

In the same way as the type of the context item can be determined for any construct C by reference to the type of the construct that establishes the context for the evaluation of C, so the posture of the context item C can be determined by reference to the posture of the construct that establishes the context.

The context posture of a construct C is the first of the following that applies:

  1. If the focus-setting container of C is an xsl:function declaration, an inline function declaration, or an xsl:on-completion element, then the context posture is roaming.

    Note:

    This is essentially an error case; expressions that depend on the context item should not normally appear within these constructs.

  2. If the focus-setting container of C is an xsl:stream instruction, then the context posture is striding.

  3. If the focus-setting container of C is a template rule whose mode is declared with streamable="yes", then the context posture is striding.

  4. If the focus-setting container of C is a pattern, then the context posture is striding.

  5. If the focus-setting container of C is an xsl:attribute-set declaration with the attribute streamable="yes", then the context posture is striding.

  6. If the focus-setting container is any other declaration, for example a global variable declaration, a named template, or a template rule or attribute set that does not specify streamable="yes", then the context posture is roaming.

  7. Otherwise, the context posture is the posture of the controlling operand of the focus-setting container of C.

19.7 The Sweep of a Construct

[Definition: Every construct has a sweep, which is a measure of the extent to which the current position in the input stream moves during the evaluation of the expression. The sweep is one of: motionless, consuming, or free-ranging .] This list of values is ordered: a free-ranging expression has wider sweep than a consuming expression, which has wider sweep than a motionless expression.

[Definition: A motionless construct is any construct deemed motionless by the rules in this section (19 Streamability).] Informally, a motionless construct is one that can be evaluated without changing the current position in the input stream.

Note:

The context item expression . is classified as motionless; however a construct that uses . as an operand (for example, string(.)) might be consuming. The streamability rules effectively consider expressions such as . within the context of the containing construct.

[Definition: A consuming construct is any construct deemed consuming by the rules in this section (19 Streamability).] Informally, a consuming construct is one whose evaluation requires repositioning of the input stream from the start of the current node to the end of the current node.

[Definition: A free-ranging construct is any construct deemed free-ranging by the rules in this section (19 Streamability).] Informally, a free-ranging construct is one whose evaluation may require access to information that is not available from the subtree rooted at the current node, together with information about ancestors of the current node and their attributes.

19.8 Classifying Constructs

This section defines the properties of every kind of construct that may appear in a stylesheet. It identifies the operand roles and their usage, and it gives the rules that define the posture and sweep of the construct. In cases where the general streamability rules apply, there is still an entry for the construct in order to define its operands and their usages, since this information is needed by the general rules.

The following sections describe this categorization for each kind of construct:

19.8.1 General Rules for Streamability

[Definition: Many constructs share the same streamability rules. These rules, referred to as the general streamability rules, are defined here.]

Examples of constructs that use these rules are: an arithmetic expression, an attribute value template, a sequence constructor, the xsl:value-of instruction, and a call to the docFO30 function.

The rules determine both the posture and sweep of a construct. To determine the posture and sweep of a construct C, assuming these general rules are applicable to that kind of construct:

  1. For each operand of C:

    1. Establish:

      1. The static type T of the operand (see 19.2 Determining the Static Type of a Construct).

      2. The sweep S and posture P of the operand (by applying the rules in this section 19.8 Classifying Constructs to that operand, recursively).

      3. The operand usage U corresponding to the role of the operand within C (from the information in this section 19.8 Classifying Constructs).

    2. Compute the adjusted sweep S' of the operand by taking the first of the following that applies:

      1. If S is free-ranging or P is roaming, then S' is free-ranging. (In this case the posture and sweep of C are roaming and free-ranging, regardless of any other operands.)

      2. If P is grounded, then S' is S.

      3. Otherwise (P is not grounded, which implies that the operand is capable of returning streamed nodes), compute S' as follows:

        1. Compute the adjusted usage U' as follows:

          1. If U is absorption and T is a childless node kind (text(), attribute(), comment(), processing-instruction, or namespace-node()), then U' is inspection.

            Note:

            This is because the entire subtree of such a node is available without reading further data from the input stream.

          2. Otherwise, U' is U.

        2. Compute the adjusted sweep S' from the table below:

          Posture (P) Adjusted Usage (U')
          Absorption Inspection Transmission Navigation
          Climbing Free-ranging S S Free-ranging
          Striding Consuming S S Free-ranging
          Crawling Free-ranging S S Free-ranging
    3. [Definition: An operand is potentially consuming if either or both of the following conditions applies:]

      1. The operand's adjusted sweep is consuming.

      2. The operand usage is transmission and the operand is not grounded.

  2. Having computed the adjusted sweep S'(o) of each operand o, the posture and sweep of C are the first of the following that applies:

    1. If C has no operands, then grounded and motionless.

    2. If any operand o has an adjusted sweep S'(o) of free-ranging, then roaming and free-ranging.

    3. If more than one operand is potentially consuming, then:

      1. If all these operands form part of a choice operand group, then the posture of C is the combined posture of the operands in this group, and the sweep of C is the widest sweep of the operands in this group

      2. Otherwise, roaming and free-ranging.

    4. If exactly one operand o is potentially consuming, then:

      1. If o is a higher-order operand of C, then roaming and free-ranging.

      2. If the operand usage of o is absorption or inspection, then grounded and consuming.

      3. If the posture of o is crawling and C is a function call of a function whose signature indicates a return type with a maximum cardinality of one (for example a call on headFO30 or exactly-oneFO30), then striding and the adjusted sweep of o.

      4. Otherwise (the operand usage of o is transmission), the posture and adjusted sweep of o.

    5. Otherwise (all operands are motionless) grounded and motionless.

Note:

The rules ensure that if more than one operand is consuming, that is, if more than one operand reads the subtree of the context node in a way that would cause the current position of the input stream to change, then the construct is not streamable.

The rules also prevent multiple streamed nodes being returned in the result of an expression unless they arise from the same axis traversal. For example, the expression count((@*, *)) is not streamable. The same applies to if (X) then @name else name. This is to make static analysis possible: the posture needs to be statically determined to ensure that streaming does not fail at execution time. It is permitted, however, for streamed nodes to be mixed in a sequence with non-streamed nodes or with atomic values; in this case the posture of the result will be that of the streamed nodes.

19.8.2 Examples of the General Streamability Rules

This section provides some examples of how the general streamability rules operate. In each example, the emphasis is on the outermost construct shown; explanations for how the sweep and posture of its operands are derived are not given, though in many cases they are explained in earlier examples.

The examples assume that the context item type for evaluation of the expression shown is an element node, and that its posture is striding.

  • 2 + 2 is grounded and motionless, because both the operands are grounded and motionless.

  • price * 2 is grounded and consuming, because one of the operands is consuming and the relevant operand usage is absorption.

  • price - discount is roaming and free-ranging, because both the operands are consuming (and they are not members of a parallel operand group).

  • price * @discount is grounded and consuming. The first operand is consuming and the corresponding operand usage is absorption, while the second operand is motionless, again with an operand usage of absorption, and its item type is attribute() which changes the effective usage to inspection.

  • a/b/c is striding and consuming. This is determined not by the general streamability rules, but by the rules for path expressions in 19.8.7.6 Streamability of Path Expressions.

  • a//c is crawling and consuming. This is similarly determined by the rules for path expressions in 19.8.7.6 Streamability of Path Expressions.

  • count(a/b/c) is grounded and consuming, because the operand (the argument to the count function) is striding and consuming (see earlier example) and the operand usage is inspection.

  • sum(a/b/c) is grounded and consuming, because the operand (the argument to the count function) is striding and consuming (see earlier example) and the operand usage is absorption.

  • count(a//c) is grounded and consuming, because the operand (the argument to the count function) is crawling and consuming (see earlier example) and the operand usage is inspection.

  • sum(a//c) is roaming and free-ranging, because the operand (the argument to the count function) is crawling and consuming (see earlier example) and the operand usage is inspection. The reason this cannot be streamed is that the c elements might have overlapping subtrees.

  • "Q{" || namespace-uri(.) || "}" || local-name(.) is grounded and motionless. The two literal operands are grounded and motionless because they have no operands; the two function calls are grounded and motionless because they have a single operand that is striding and motionless, with an operand usage of inspection.

  • copy-of(.)/head/following-sibling::* is grounded and consuming. The first operand copy-of(.)/head is grounded and consuming because, under the rules in 19.8.7.6 Streamability of Path Expressions, its first operand copy-of(.) is grounded and consuming. This in turn is because . is striding and motionless, and the operand usage is absorption.

  • distinct-values((., @code)) is roaming and free-ranging. Although it is not difficult to identify a strategy for evaluating this in a streaming manner, the static analysis rules make an expression free-ranging if it has two operands with different posture. This is because in general this prevents streamability being determined statically.

  • if ($discounted) then price else discounted-price is striding and consuming, because the two branches of the conditional are both striding and consuming, and they form an choice operand group with usage transmission.

  • if ($gratis) then 0 else price else is striding and consuming because there is only one consuming operand (the fact that it is part of a choice operand group does not affect the reasoning).

  • count((author, editor)) is roaming and free-ranging. The first argument to the count function is an expression with two operands, both having usage=transmission, and neither being grounded.

  • count((author | editor)) is grounded and consuming. A union expression is not subject to the general streamability rules; it has its own rules, defined in 19.8.7.4 Streamability of union, intersect, and except expressions, which establish in this case that the argument to the countFO30 is crawling and consuming. The countFO30 function does follow the general streamability rules, with an operand usage of inspection: under rule 1(b)(iii)(B) the adjusted sweep is consuming, and rule 2(d)(iii) then applies.

  • ('{', author, '}') is striding and consuming. Exactly one operand is consuming; it has usage transmission, so the result has the posture and sweep of that operand. (The formal analysis treats comma as a binary operator, but the same result can be obtained by treating the content of the parenthesized expression as an expression with three operands.)

19.8.3 Classifying Sequence Constructors

The posture and sweep of a sequence constructor are determined by the general streamability rules.

The operand roles for a sequence constructor are:

  1. The contained instructions. The operand usage for these operands is transmission.

  2. Any text value templates appearing in text nodes within the sequence constructor, if text value templates are enabled. The operand usage for these operands is absorption.

Note:

Some consequences of these rules are:

  1. An empty sequence constructor is motionless, and its posture is grounded.

  2. A sequence constructor containing a single instruction has the same sweep and posture as that instruction.

    Note:

    This means that sequence constructors containing a single instruction can usefully be dropped from the construct tree.

  3. Informally, a sequence constructor is not streamable if it contains more than one instruction that moves the position of the input stream.

Instructions within a sequence constructor are further classified to control the use of accumulator functions:

  1. [Definition: A motionless instruction having no consuming instruction as a preceding sibling is referred to as a pre-descent instruction.]

  2. [Definition: A motionless instruction having no consuming instruction as a following sibling is referred to as a post-descent instruction.]

  3. In addition, the following are classified as post-descent instructions:

    1. Any instruction whose parent is an xsl:if instruction, if the test expression is a consuming expression;

    2. Any instruction whose parent is an xsl:when instruction, if the test expression of the parent xsl:when or of any preceding sibling of the parent xsl:when is a consuming expression

In the above rules, an instruction is considered to be consuming if its adjusted sweep S' is consuming, as defined by the the general streamability rules when applied to the containing sequence constructor.

Note:

This means that for templates that match text or attribute nodes, an instruction such as <xsl:value-of select="."/> is not consuming, which means that all instructions in the template rule qualify as both pre-descent and post-descent instructions. The same can happen in a template rule that does not access the string value or typed value of the context item.

19.8.4 Classifying Instructions

This section describes how instructions are classified with respect to their streamability. The criteria are given first for literal result elements and extension instructions,, then for each XSLT instruction, listed alphabetically.

19.8.4.1 Streamability of Literal Result Elements

The posture and sweep of a literal result element follow the general streamability rules. The operand roles and their usages are:

  1. The contained sequence constructor (usage absorption)

  2. Any expressions contained in attribute value templates among the literal result element's attributes (usage absorption)

  3. Any attribute sets named in the xsl:use-attribute-sets attribute (usage absorption).

19.8.4.2 Streamability of extension instructions

For a processor that recognizes an extension instruction, the posture and sweep of the instruction are implementation-defined.

For a processor that does not recognize an extension instruction, the posture and sweep of the instruction are determined by applying the general streamability rules, The operand roles and their usages are:

  1. The sequence constructors contained in any xsl:fallback children (usage transmission)

Instructions in the XSLT namespace that are present under the provisions for forwards compatible behavior are treated in the same way as unrecognized extension instructions.

Note:

These rules mean that if there is no xsl:fallback child instruction, the containing construct will be classified as streamable. However, any attempt to execute the instruction will lead to a dynamic error, so in fact, neither streamed nor unstreamed evaluation is possible.

19.8.4.3 Streamability of xsl:analyze-string

The posture and sweep of xsl:analyze-string follow the general streamability rules. The operand roles and their usages are:

  1. the select expression (usage absorption);

  2. the regex attribute value template (usage absorption);

  3. the sequence constructors contained in the xsl:matching-substring and xsl:non-matching-substring elements. These have usage navigation, because they can be evaluated more than once. The context posture for the two sequence constructors is grounded, reflecting the fact that their context item type is xs:string.

Note:

In practice, the sweep of the instruction will usually be the same as the sweep of the select expression, and its posture will be grounded. Exceptions occur for example if the regex attribute is not motionless, or if the contained sequence constructors refer to a grouping variable bound in a contained xsl:for-each-group instruction.

19.8.4.4 Streamability of xsl:apply-imports

The rules in this section apply also to xsl:next-match.

The posture and sweep of these two instructions follow the general streamability rules. The operand roles and their usages are:

  1. An implicit operand: a context item expression (.), with usage absorption;

  2. The select attribute or contained sequence constructor of each xsl:with-param child element, with type-determined usage based on the type declared in the xsl:with-param/@as attribute, or item()* if absent.

Note:

The instruction will normally be grounded and consuming, provided that nodes in a streamed document are not passed as parameters to the called template rule.

19.8.4.5 Streamability of xsl:apply-templates

If there is no select attribute, the following analysis assumes the presence of an implicit operand select="child::node()".

The posture and sweep of the xsl:apply-templates instruction are the first of the following that apply:

  1. If the select expression is grounded, then the posture and sweep of the xsl:apply-templates instruction follow the general streamability rules, with the operand roles and their usages as follows:

    1. The select expression (the operand usage is irrelevant, but can be taken as absorption)

    2. The select expressions and contained sequence constructors of any child xsl:with-param elements (usage type-determined, based on the type in the xsl:with-param/@as attribute, defaulting to item()*)

    3. Any attribute value templates appearing in attributes of a child xsl:sort instruction (usage absorption)

    4. The select expression or contained sequence constructor of any xsl:sort children, assessed with a context posture of grounded (usage absorption).

    For example, <xsl:apply-templates select="copy-of(.)"/> is grounded and consuming.

  2. If there is an xsl:sort child element, then roaming and free-ranging.

  3. If the implicit or explicit mode attribute identifies a mode that is not declared with streamable="yes", then roaming and free-ranging.

    Note:

    When mode="#current" is specified, this is treated as equivalent to specifying a streamable mode; although it is not known statically what the mode will be, it is always the case that if the template is invoked with a streamed node as the context item, the the current mode must be a streamable mode.

  4. Otherwise, the posture and sweep of the xsl:apply-templates instruction follow the general streamability rules. The operand roles and their usages are as follows:

    1. The (explicit or implicit) select expression, with usage absorption;

    2. The select attribute or contained sequence constructor of each xsl:with-param child element, with type-determined usage based on the type declared in the xsl:with-param/@as attribute, or item()* if absent.

19.8.4.6 Streamability of xsl:assert

The posture and sweep of xsl:assert follow the general streamability rules. The operand roles and their usages are as follows:

  1. The test expression (usage inspection)

  2. The select expression (usage absorption)

  3. The contained sequence constructor (usage absorption).

19.8.4.7 Streamability of xsl:attribute

The posture and sweep of xsl:attribute follow the general streamability rules. The operand roles and their usages are as follows:

  1. The name attribute value template (usage absorption)

  2. The namespace attribute value template (usage absorption)

  3. The select expression (usage absorption)

  4. The separator attribute value template (usage absorption)

  5. The on-empty expression (usage absorption)

  6. The contained sequence constructor (usage absorption).

19.8.4.8 Streamability of xsl:break

The posture and sweep of xsl:break follow the general streamability rules. The operand roles and their usages are as follows:

  1. The select expression (usage transmission)

  2. The contained sequence constructor (usage transmission).

19.8.4.9 Streamability of xsl:call-template

The posture and sweep of xsl:call-template follow the general streamability rules. The operand roles and their usages are as follows:

  1. Unless the referenced template has a child xsl:context-item element with the attribute use="prohibited", there is an implicit operand, a context item expression (.): its operand usage is the type-determined usage based on the type declared in the xsl:context-item/@as attribute of the target named template, defaulting to item()* if absent.

  2. The select expression or sequence constructor content of any contained xsl:with-param child element: its operand usage is the type-determined usage based on the type declared in the xsl:with-param/@as attribute, or the xsl:param/@as attribute of the corresponding parameter on the target named template, whichever is more restrictive, defaulting to item()* if both are absent.

Note:

Calling xsl:call-template will usually make stylesheet code unstreamable if a streamed node is passed explicitly or implicitly to the called template, unless it is atomized by declaring the expected type to be atomic.

19.8.4.10 Streamability of xsl:choose

The posture and sweep of xsl:choose follow the general streamability rules. The operand roles and their usages are as follows:

  1. The test attribute of contained xsl:when elements (usage inspection).

  2. The sequence constructors contained within xsl:when and xsl:otherwise child elements (usage transmission). These sequence constructor operands form a choice operand group.

Note:

The effect is to allow any of the following:

  1. Every sequence constructor in an xsl:when or xsl:otherwise branch may read the input stream. In this situation the test expressions must be motionless.

  2. Alternatively, the first test expression may consume the input stream, in which case the sequence constructors (and any subsequent test expresssions) must be motionless.

19.8.4.11 Streamability of xsl:comment

The posture and sweep of xsl:comment follow the general streamability rules. The operand roles and their usages are as follows:

  1. The select expression (usage absorption)

  2. The contained sequence constructor (usage absorption).

19.8.4.12 Streamability of xsl:copy

The posture and sweep of xsl:copy follow the general streamability rules. The operand roles and their usages are as follows:

  1. The expression in the select attribute, defaulting to a context item expression (.) (usage inspection)

  2. The contained sequence constructor (usage absorption), assessed with context posture and context item type based on the select expression if present, or the outer focus otherwise.

  3. Any attribute-sets named in the use-attribute-sets attribute (usage absorption)

  4. The expression contained in the on-empty attribute, if present (usage absorption).

19.8.4.13 Streamability of xsl:copy-of

The posture and sweep of xsl:copy-of follow the general streamability rules. The operand roles and their usages are as follows:

  1. The select expression (usage absorption).

19.8.4.14 Streamability of xsl:document

The posture and sweep of xsl:document follow the general streamability rules. The operand roles and their usages are as follows:

  1. The contained sequence constructor (usage absorption).

19.8.4.15 Streamability of xsl:element

The posture and sweep of xsl:element follow the general streamability rules. The operand roles and their usages are as follows:

  1. The name attribute value template (usage absorption)

  2. The namespace attribute value template (usage absorption)

  3. The on-empty expression (usage absorption)

  4. The attribute sets named in the use-attribute-sets attribute (usage absorption)

  5. The contained sequence constructor (usage absorption).

19.8.4.16 Streamability of xsl:evaluate

The posture and sweep of xsl:evaluate follow the general streamability rules. The operand roles and their usages are as follows:

  1. The xpath expression (usage absorption)

  2. The context-item expression (usage navigation)

  3. The with-params expression (usage navigation)

  4. The base-uri attribute value template (usage absorption)

  5. The namespace-context expression (usage inspection)

  6. The select attributes and contained sequence constructors of any xsl:with-param child elements (usage type-determined, based on the type in the xsl:with-param/@as attribute, defaulting to item()*)

Note:

In practice, code containing an xsl:evaluate instruction will usually be streamable provided that streamed nodes are not passed to the dynamic expression either as the context item or as the value of a parameter.

19.8.4.17 Streamability of xsl:for-each

The posture and sweep of the xsl:for-each instruction are the first of the following that applies:

  1. If the select expression is grounded, then the posture and sweep of the xsl:for-each instruction follow the general streamability rules, with the operand roles and their usages as follows:

    1. The select expression (the operand usage is irrelevant, but can be taken as inspection)

    2. The contained sequence constructor (usage transmission). This is a higher-order operand; its context posture is grounded.

    3. Any attribute value templates appearing in attributes of a child xsl:sort instruction (usage absorption)

    4. The select expression or contained sequence constructor of any xsl:sort children, assessed with a context posture of grounded (usage absorption). These are higher-order operands; their context posture is grounded.

  2. If there is an xsl:sort child element, then roaming and free-ranging.

  3. Otherwise:

    1. The posture of the instruction is the posture of the contained sequence constructor, assessed with the context posture and context item type set to the posture and type of the select expression.

    2. The sweep of the instruction is the wider of the sweep of the select expression and the sweep of the contained sequence constructor.

      Note:

      The ordering of sweep values is in increasing order: motionless, consuming, free-ranging.

19.8.4.18 Streamability of xsl:for-each-group

The posture and sweep of the xsl:for-each-group instruction are the first of the following that applies:

  1. If the select expression is grounded, then the posture and sweep of the xsl:for-each-group instruction follow the general streamability rules, with the operand roles and their usages as follows:

    1. The select expression (the operand usage is irrelevant, but can be taken as inspection)

    2. The collation attribute value template (usage absorption)

    3. Any attribute value templates appearing in attributes of a child xsl:sort instruction (usage absorption)

    4. The group-by or group-adjacent expression, assessed with a context posture of grounded (usage absorption).

    5. The select expression or contained sequence constructor of any xsl:sort children, assessed with a context posture of grounded (usage absorption).

    6. The group-starting-with or group-ending-with patterns if present; these are higher-order operands with usage inspection.

  2. If there is a group-by attribute, then roaming and free-ranging.

  3. If there is a group-adjacent attribute that is not motionless, then roaming and free-ranging.

  4. If there is an xsl:sort child element, then roaming and free-ranging.

  5. If there is no bind-group attribute, then roaming and free-ranging.

  6. If there is a group-adjacent attribute but no bind-grouping-key attribute, then roaming and free-ranging.

  7. Otherwise:

    1. The posture of the instruction is the posture of the contained sequence constructor, assessed with the context posture and context item type set to the posture and type of the select expression.

    2. The sweep of the instruction is the wider of the sweeps of the select expression and the contained sequence constructor, where the ordering of increasing width is motionless, consuming, free-ranging.

Note:

The above rules do not explicitly mention any constraints on the presence or absence of a variable reference to the variable bound in the bind-group attribute of the xsl:for-each-group instruction. In practice, however, this plays an important role. In the most common case, the select expression of xsl:for-each-group is likely to be striding, for example an expression that selects all the children of a given element. If the instruction binds a variable $group using the bind-group attribute, then any reference to this variable will ordinarily be striding and consuming, which is consistent with streaming provided there is only one such reference, and if it appears in a suitable context (for example, not within a predicate). If there is more than one reference to the grouping variable, or if it appears in an unsuitable context (for example, within a predicate), then this will have the same effect as multiple appearances of other consuming expressions: the construct as a whole will be free-ranging. These rules are not spelled out explicitly, but rather emerge as a consequence of the general streamability rules.

19.8.4.19 Streamability of xsl:fork

The posture and sweep of xsl:fork are the first of the following that applies:

  1. If there are no child xsl:sequence instructions, then grounded and motionless.

  2. If there is exactly one child xsl:sequence instruction that is not grounded and motionless, then the posture and sweep of that instruction.

  3. If any of the child xsl:sequence instructions is roaming or free-ranging, then roaming and free-ranging.

  4. If the posture of any of the child xsl:sequence instructions is not grounded, then roaming and free-ranging.

    Note:

    This means that none of the branches of xsl:fork can return streamed nodes. The reason for this is that xsl:fork has to assemble its results in the correct order, and streamed nodes cannot be re-ordered.

  5. Otherwise, grounded and consuming

Note:

The effect of the rules is that each of the child xsl:sequence instructions can independently consume the streamed input document, provided that the result of each child instruction is grounded.

Thus the following example is streamable:

<xsl:fork>
   <xsl:sequence select="copy-of(author)"/>
   <xsl:sequence select="copy-of(editor)"/>
</xsl:fork>

While the following is not streamable:

<xsl:fork>
   <xsl:sequence select="author"/>
   <xsl:sequence select="editor"/>
</xsl:fork>

This is because the latter example attempts to return a sequence of streamed nodes in an order which might not be document order.

The only case where xsl:fork is permitted to return streamed nodes is in the case where only one of the xsl:sequence instructions is consuming (in which case the xsl:fork instruction is pointless).

19.8.4.20 Streamability of xsl:if

The posture and sweep of xsl:if follow the general streamability rules. The operand roles and their usages are as follows:

  1. The test expression (usage inspection)

  2. The contained sequence constructor (usage transmission).

19.8.4.21 Streamability of xsl:iterate

The posture and sweep of the xsl:iterate instruction are the first of the following that applies:

  1. If the select expression is grounded, then the posture and sweep of the xsl:iterate instruction follow the general streamability rules, with the operand roles and their usages as follows:

    1. The select expression (the operand usage is irrelevant, but can be taken as inspection)

    2. The select expression or contained sequence constructor of any xsl:param children (usage navigation)

    3. The sequence constructor contained within the xsl:iterate instruction itself, assessed with its content item type and context posture based on the select expression (usage transmission)

    4. The select expression or contained sequence constructor of any child xsl:on-completion element, assessed with a content item type of xs:error and a context posture of roaming to reflect the fact that any attempt to reference the context item within the xsl:on-completion element is an error (usage transmission)

  2. Otherwise:

    1. The posture of the instruction is the posture of the contained sequence constructor, assessed with the context posture and context item type set to the posture and type of the select expression.

    2. The sweep of the instruction is the wider of the sweeps of the two operands, where the ordering of increasing width is motionless, consuming, free-ranging.

Note:

If any xsl:break or xsl:next-iteration instructions appear within the sequence constructor, their posture and sweep will be assessed in the course of evaluating the posture and sweep of the sequence constructor, by reference to the rules in 19.8.4.8 Streamability of xsl:break and 19.8.4.27 Streamability of xsl:next-iteration respectively.

19.8.4.22 Streamability of xsl:map

The posture and sweep of the xsl:map instruction are determined by the first of the following that applies:

  1. If the sequence constructor within the instruction consists exclusively of xsl:map-entry instructions (and xsl:fallback instructions, which are ignored), and if none of those xsl:map-entry children is roaming or free-ranging, then the posture of the xsl:map instruction is grounded and the sweep is the widest sweep of the xsl:map-entry children.

  2. Otherwise, the posture and sweep of the xsl:map instruction are the posture and sweep of the contained sequence constructor.

Note:

See discussion in 21.1.5 Maps and Streaming.

The effect of the rules is that it is possible to compute multiple map entries in a single pass of the streamed input document. For example, the following is streamable:

<xsl:map>
  <xsl:map-entry key="'authors'" select="copy-of(author)"/>
  <xsl:map-entry key="'editors'" select="copy-of(editor)"/>
</xsl:map>  

The call on copy-of is necessary to ensure that the content of the map entry is grounded; it is not possible to create a map whose entries contain references to streamed nodes.

19.8.4.23 Streamability of xsl:map-entry

The posture and sweep of xsl:map-entry follow the general streamability rules. The operand roles and their usages are as follows:

  1. The key expression (usage absorption)

  2. The select expression (usage navigation)

    Note:

    This effectively means that the select expression must not return nodes from a streamed input document.

  3. The contained sequence constructor (usage navigation).

19.8.4.24 Streamability of xsl:merge

If all xsl:merge-source children are motionless then the instruction is motionless.

Otherwise, the instruction is free-ranging.

Note:

The xsl:merge instruction will often process its input using streaming, but the rule here is concerned with the sweep of the instruction with respect to the document containing the context node, which will not usually be one of the primary inputs to the merging process. A merge operation that processes several input documents in a streaming manner might thus be classified as free-ranging with respect to the principal source document of the transformation.

A more ambitious implementation might attempt to recognize the case where one of the merge sources involves consuming a subtree of the principal source document: that is, the case where one merge source is a consuming expression and the other sources are motionless.

19.8.4.25 Streamability of xsl:message

The posture and sweep of xsl:message follow the general streamability rules. The operand roles and their usages are as follows:

  1. The select expression (usage absorption)

  2. The terminate attribute value template (usage absorption)

  3. The contained sequence constructor (usage absorption).

19.8.4.26 Streamability of xsl:namespace

The posture and sweep of xsl:namespace follow the general streamability rules. The operand roles and their usages are as follows:

  1. The name attribute value template (usage absorption)

  2. The select expression (usage absorption)

  3. The contained sequence constructor (usage absorption).

19.8.4.27 Streamability of xsl:next-iteration

The posture and sweep of xsl:next-iteration follow the general streamability rules. The operand roles and their usages are as follows:

  1. The select expression or sequence constructor content of any contained xsl:with-param child element: its operand usage is the type-determined usage based on the type declared in the xsl:with-param/@as attribute, or the xsl:param/@as attribute of the corresponding parameter on the containing xsl:iterate instruction, whichever is more restrictive, defaulting to item()* if both are absent.

19.8.4.29 Streamability of xsl:number

The posture and sweep of xsl:number follow the general streamability rules. The operand roles and their usages are as follows:

  1. The value attribute if present (usage absorption)

  2. The select attribute if present (usage navigation)

  3. The attribute value templates in the format, lang, letter-value, ordinal, start-at, grouping-separator, and grouping-size attributes (usage absorption)

  4. The from and count patterns if present; these are higher-order operands with usage inspection.

Note:

The effect of these rules is that xsl:number can be used for formatting of numbers supplied directly, and for numbering of nodes in a non-streamed document, but cannot be used for numbering streamed nodes.

In practice the rules depend very little on the from and count patterns. This is because when the instruction is applied to a streamed node, the instruction will be free-ranging regardless of these patterns; while if it is applied to a grounded node or atomic value, the instruction will be motionless regardless of the values of these patterns. The only restriction is that the patterns must not reference a grouping variable.

19.8.4.30 Streamability of xsl:perform-sort

The posture and sweep of xsl:perform-sort follow the general streamability rules. The operand roles and their usages are as follows:

  1. The expression in the select attribute: usage navigation (because order is not preserved)

  2. The expressions in the attribute value templates of xsl:sort child elements: usage absorption

  3. The expression in the select attribute or contained sequence constructor in child xsl:sort child elements, with usage absorption, assessed with context posture based on the expression in the xsl:perform-sort/@select attribute.

Note:

In practice, the xsl:perform-sort instruction cannot be used to sort nodes from the streamed input document, but it can be used to sort atomic values or grounded nodes, for example a copy of nodes from the streamed document made using the copy-of function.

19.8.4.31 Streamability of xsl:processing-instruction

The posture and sweep of xsl:processing-instruction follow the general streamability rules. The operand roles and their usages are as follows:

  1. The name attribute value template (usage absorption)

  2. The select expression (usage absorption)

  3. The contained sequence constructor (usage absorption).

19.8.4.32 Streamability of xsl:result-document

The posture and sweep of xsl:result-document follow the general streamability rules. The operand roles and their usages are as follows:

  1. The href attribute value template (usage absorption)

  2. The attribute value templates containing serialization properties (usage absorption)

  3. The contained sequence constructor (usage absorption).

19.8.4.33 Streamability of xsl:sequence

The posture and sweep of xsl:sequence follow the general streamability rules. The operand roles and their usages are as follows:

  1. The select attribute value template (usage transmission)

  2. The contained sequence constructor (usage transmission).

19.8.4.34 Streamability of xsl:stream

Note:

The concern here is with the impact of xsl:stream on any streaming template, or ancestor xsl:stream instruction, and not with the streamed processing of the document accessed using the xsl:stream/@href attribute.

The streamability of the document opened by the xsl:stream instruction is not assessed using the rules in this section; it depends only on the streamability properties of the contained sequence constructor, as described in 18.1 The xsl:stream Instruction

The posture and sweep of xsl:stream are the first of the following that applies:

  1. If the contained sequence constructor contains, at any depth, a variable reference whose binding is a bind-group attribute of an xsl:for-each-group or xsl:merge instruction that is itself an ancestor of the xsl:stream instruction, then roaming and free-ranging.

  2. Otherwise, the posture is grounded and the sweep is the sweep of the href attribute value template.

Note:

The effective prohibition on grouping variable references is largely to avoid complicating the analysis. It means that posture and sweep for the constructs within xsl:stream need to be computed only with respect to the xsl:stream instruction itself, and not with respect to the containing template, or an outer xsl:stream instruction.

19.8.4.35 Streamability of xsl:text

The posture and sweep of xsl:text follow the general streamability rules. There are no operands.

Note:

The instruction is therefore grounded and motionless.

19.8.4.36 Streamability of xsl:try

The sweep of the instruction is the first of the following that applies:

  1. If the select expression and/or sequence constructor of the xsl:catch element are motionless, then the sweep of the select expression and/or sequence constructor of the xsl:try element (whichever is present);

  2. Otherwise, free-ranging.

19.8.4.37 Streamability of xsl:value-of

The posture and sweep of xsl:value-of follow the general streamability rules. The operand roles and their usages are as follows:

  1. The select expression (usage absorption)

  2. The separator attribute value template (usage absorption)

  3. The contained sequence constructor (usage absorption).

19.8.4.38 Streamability of xsl:variable

The posture and sweep of xsl:variable follow the general streamability rules. The operand roles and their usages are as follows:

  1. The select expression (usage navigation)

  2. The contained sequence constructor (usage navigation).

Note:

The effect of the initialization expression having usage navigation is that it is not possible in streamable constructs to bind a variable to a node in a streamed document.

19.8.5 Classifying Attribute Sets

The general streamability rules apply to attribute sets. The operand roles and their usages are:

  1. Any xsl:attribute instruction contained in any of the xsl:attribute-set declarations making up the attribute set. (Usage transmission)

  2. Any attribute set referenced by a use-attribute-sets attribute in any of the xsl:attribute-set declarations making up the attribute set. (Usage transmission)

The sweep of an attribute set is determined using the general rules in 19.8.1 General Rules for Streamability.

Note:

Attribute sets will always be grounded, because they return newly constructed attribute nodes.

Attribute sets will very often be motionless, but if they access the context item, they may be consuming or free-ranging.

Because attribute sets can be overridden in another package, the streamability of a construct such as an xsl:element instruction containing a use-attribute-sets attribute is based on the declared streamability of the named attribute sets, as defined by the streamable attribute of the xsl:attribute-set element. If streamable="yes" is specified, then there is a requirement that any overriding attribute set should also specify streamable="yes", and a streaming processor is required to check that an attribute set containing such a declaration does in fact satisfy the streamability rules.

19.8.6 Classifying Value Templates

A value template (that is, an attribute value template or text value template) is a construct whose operands are the expressions contained within curly braces. The required type for this operand role is xs:string and the usage is absorption.

The sweep and posture of a value template are determined using the general rules in 19.8.1 General Rules for Streamability.

If there are no expressions contained within curly braces, the value template is motionless.

19.8.7 Classifying Expressions

XPath expressions are classified using the rules in this section.

In the analysis that follows, expressions are classified according to the most specific production rule that they match for which there is an entry in this section. For example, the expression 3 satisfies the productions NumericLiteral, Literal, and ArithmeticExpression; the most specific of these for which there is an entry in this section is Literal. A production P is considered more specific than a production Q (QP) if every expression that matches P also matches Q.

The production rules for different kinds of expression are listed (with their names and numbers) in the order in which they appear in Appendix A.1 of the XPath 3.0 specification.

Many expressions can be analyzed using the general streamability rules. These are indicated in the table below by means of a simple proforma in which the operand roles are represented by a short code (A = absorption, I = inspection, T = transmission, N = navigation). For example the proforma A + A indicates that for an arithmetic expression, both operands have operand usage absorption, while I or I indicates that for an or expression, both operands have operand usage inspection. For expressions where further explanation is needed, the table contains a link to the relevant section.

Construct Proforma or Reference to Detailed Rules Further Information
Expr [6] T, T
ForExpr [8] See 19.8.7.1 Streamability of for expressions
LetExpr [11] let $var := N return T Binding of variables to streamed nodes is not allowed.
QuantifiedExpr [14] See 19.8.7.2 Streamability of Quantified Expressions
IfExpr [15] if (I) then T else T The then-clause and else-clause form a choice operand group with usage transmission
OrExpr [16] I or I
AndExpr [17] I and I
StringConcatExpr [19] A || A
RangeExpr [20] A to A
AdditiveExpr [21] A + A, A - A
MultiplicativeExpr [22] A * A, A div A, etc
UnionExpr [23] See 19.8.7.4 Streamability of union, intersect, and except expressions
IntersectExceptExpr [24] See 19.8.7.4 Streamability of union, intersect, and except expressions
InstanceOfExpr [25] I instance of TYPE
TreatExpr [26] T treat as TYPE
CastableExpr [27] A castable as TYPE
CastExpr [28] A cast as TYPE
UnaryExpr [29] +A, -A
GeneralComp [31] A = A, A < A, A != A, etc
ValueComp [32] A eq A, A lt A, A ne A, etc
NodeComp [33] I is I, I << I, I >> I
SimpleMapExpr [34] See 19.8.7.5 Streamability of Simple Mapping Expressions
PathExpr [35] See 19.8.7.6 Streamability of Path Expressions
RelativePathExpr [36] See 19.8.7.6 Streamability of Path Expressions
AxisStep [38] See 19.8.7.7 Streamability of Axis Steps
ForwardStep [39] , ReverseStep [42] See 19.8.7.7 Streamability of Axis Steps
PostfixExpr [48]: Filter Expression See 19.8.7.8 Streamability of Filter Expressions
PostfixExpr [48]: Dynamic Function Call See 19.8.7.9 Streamability of Dynamic Function Calls
Literal [53] There are no operands, so the construct is grounded and motionless
VarRef [55] See 19.8.7.10 Streamability of Variable References
ParenthesizedExpr [57] (T)
() There are no operands, so the construct is grounded and motionless
ContextItemExpr [58] See 19.8.7.11 Streamability of the Context Item Expression
FunctionCall [59] See 19.8.7.12 Streamability of Function Calls
NamedFunctionRef [63] See 19.8.7.13 Streamability of Named Function References
InlineFunctionExpr [64] See 19.8.7.14 Streamability of Inline Function Declarations
MapExpr [202] See 19.8.7.15 Streamability of map expressions
19.8.7.1 Streamability of for expressions

Writing the expression as for $v in S return R, the two operand roles are S and R.

The posture and sweep are determined by the first of the following that applies:

  1. If R is not grounded, then roaming and free-ranging.

  2. Otherwise, the general streamability rules apply. The operand roles are:

    1. The in expression (S). This has usage navigation.

    2. The return expression (R). This is a higher-order operand with usage transmission.

Note:

Expressions of the form for $i in 1 to 3 return $i*2, where there is no reference to a streamed node, are clearly streamable.

The in expression can also be consuming, for example for $e in copy-of(emp) return $e/salary.

The rule that R must be grounded prevents the variable being bound to a node in a streamed document. This disallows expressions of the form for $x in child::section return $x/para, because this requires data flow analysis (tracing from the binding of a variable to its usages), rather than purely syntactic analysis. Some implementations may be able to stream such constructs.

The fact that the return clause is a higher-order operand prevents it from being a consuming expression, for example for $i in 1 to 3 return salary. Use of a motionless expression that accesses streamed nodes is however allowed, for example for $i in 1 to 3 return name(ancestor::x[$i]).

19.8.7.2 Streamability of Quantified Expressions

Writing the expression as some|every $v in S satisfies C, the two operand roles are S and C.

The posture and sweep are determined by the first of the following that applies:

  1. If C is not motionless, then roaming and free-ranging.

  2. Otherwise, the posture and sweep of S.

19.8.7.3 Streamability of if expressions

Writing the expression as if (C) then T else E, there are three operand roles: C, T, and E. The usage of C is inspection, while the usage of T and E is transmission. Operands T and E form a choice operand group, meaning that they can both consume the input stream, provided they have consistent posture. The general streamability rules apply.

19.8.7.4 Streamability of union, intersect, and except expressions

The posture and sweep are the first of the following that applies:

  1. If either of the two operands is free-ranging, then roaming and free-ranging (Example: . | following-sibling::*).

  2. If either of the two operands is grounded and motionless, then the posture and sweep of the other operand (Example: . | doc('abc.com')//x)

  3. If both operands are climbing and motionless, then climbing and motionless (Example: @x | @y)

  4. If both operands are striding or crawling, then crawling and the wider of the sweeps of the two operands (Example: * | */*).

  5. Otherwise, roaming and free-ranging (Example: name | @name).

Note:

Essentially the principle is that if both operands are streamable, then the result is streamable (this assumes an evaluation strategy where both operands are evaluated during the same pass of the streamed input document, and the results merged). But there are caveats because of the need for static streamability analysis of the result. This prevents constructs such as .. | * that have heterogeneous posture.

Where the two operands are both striding, there are cases where an implementation could determine that the result is also striding: for example (author | editor). In general, however, the combination of two striding operands may produce a sequence of nodes that have overlapping subtrees (consider author | author/name), so the result is classified as crawling.

The expression (author | editor), although it is not striding, can be rewritten in the form *[self::author or self::editor], which is striding.

19.8.7.5 Streamability of Simple Mapping Expressions

The mapping operator ! is treated as a left-associative binary operator, so the expression a!b!c is processed as (a!b)!c.

The posture and sweep of the expression are the posture and sweep of the right-hand operand, assessed with a context posture and type set to the posture and type of the first operand.

19.8.7.6 Streamability of Path Expressions

The streamability analysis applies after the expansion of the // pseudo-operator to /descendant-or-self::node()/, and after expanding .. to parent::node(), @X to attribute::X, and an omitted axis to child::.

Following the rules in XPath, a leading "/" is converted to (root(self::node()) treat as document-node())/ (with the final "/" omitted for the expression "/" on its own). This is followed by a rewrite of the call on rootFO30, as described in 19.8.8.10 Streamability of the root function.

Note:

Taken together, these rewrites have the effect that a path expression such as //a is streamable only if the statically-determined context item type is document-node(), which will be the case for example immediately within xsl:stream, or in a template rule with match="/".

A RelativePathExpr with more than two operands (such as a/b/c) is taken as a tree of binary expressions (that is, (a/b)/c). This prevents some optimizations which are possible if the RelativePathExpr is considered as a whole: these optimizations should be applied by rewriting the tree before this analysis takes place, as described in 19.1 An Optimization: Pattern-Based Scanning.

The posture of the expression is the posture of the right-hand operand, assessed with a context posture and type set to the posture and type of the first operand.

Note:

Examples:

  • If the context posture is striding, then the posture of the expression a/b/c is striding, because (under the rules for AxisStep [38]) a child axis step evaluated with striding posture creates a new striding posture.

  • If the context posture is striding, then the posture of the expression a//c is crawling, because a descendant axis step evaluated with striding posture creates a new crawling posture.

  • If the context posture is striding, then the posture of the expression ../@status is climbing, because a parent axis step evaluated with striding posture creates a new climbing posture, and an attribute axis step evaluated with climbing posture creates a new climbing posture.

  • If the context posture is striding, then the posture of the expression copy-of(.)//a/following-sibling::* is grounded, because the copy-of evaluated with striding posture creates a grounded posture, and all subsequent axis steps leave this posture unchanged.

The sweep of the expression is the wider sweep of the two operands, where the ordering of increasing width is motionless, consuming, free-ranging.

Note:

Examples:

19.8.7.7 Streamability of Axis Steps

The sweep and posture of the expression are determined by the first of the following rules that applies:

  1. If the context posture is grounded, then the sweep is motionless and the posture is grounded;

  2. If the context posture is roaming, then the sweep is free-ranging and the posture is roaming;

  3. If the statically-inferred context item type is such that the axis will always be empty (for example, applying the child axis to a text node or the parent axis to a document node), then the sweep is motionless and the posture is grounded (because the expression is statically known to return an empty sequence);

  4. If the context posture is striding, and the axis is descendant or descendant-or-self, and there is a predicate in the PredicateList that is either a numeric literal or a reference to a variable whose declared type is numeric (for example, descendant::title[1]), then striding and consuming;

  5. If the PredicateList contains a Predicate that is not motionless, then the sweep is free-ranging and the posture is roaming;

  6. Otherwise, the sweep and posture of the expression are as determined by the table below, based on the context posture and the choice of axis:

    Context posture Axis Result posture Sweep
    Grounded any Grounded Motionless
    Climbing self, parent, ancestor-or-self, ancestor, attribute, namespace Climbing Motionless
    Striding parent, ancestor-or-self, ancestor, attribute, namespace Climbing Motionless
    Striding self Striding Motionless
    Striding child Striding Consuming
    Striding descendant, descendant-or-self Crawling Consuming
    Crawling parent, ancestor-or-self, ancestor, attribute, namespace Climbing Motionless
    Crawling self Crawling Motionless
    Any other combination Roaming Free-ranging

Note:

This analysis does not attempt to classify para[title] as a consuming expression; an implementation might choose to do so.

19.8.7.8 Streamability of Filter Expressions

For a filter expression of the form B[P] (where B might itself be a filter expression), the posture and sweep are the first of the following that applies:

  1. If B is crawling and consuming, and B is either a numeric literal, or a reference to a variable whose declared type is numeric, then crawling and consuming

  2. If P is motionless, then the posture and sweep of B;

  3. Otherwise, roaming and free-ranging.

Note:

The first rule allows a construct such as <xsl:apply-templates select="(//title)[1]"/>, where a crawling operand would not be guaranteed streamable.

Note:

This section is not applicable to predicates forming part of an axis step, such as //title[1], as these are not technically filter expressions. See 19.8.7.7 Streamability of Axis Steps.

19.8.7.9 Streamability of Dynamic Function Calls

For a dynamic function call such as $F(X, Y), the general rule in 19.8.1 General Rules for Streamability applies. The operands of a dynamic function call are the expression that computes the function value itself (here $F), and the argument expressions (here X and Y).

The operand usage of the first operand is inspection, reflecting the fact that the only action needed at evaluation time is to inspect the value (if it is a node, a type error is raised).

The operand usage for the other operands (the argument expressions) is in general navigation, because it is not known how the function will make use of any supplied nodes. However, if the static type of the first operand constrains the type of the argument to be atomic, then the operand usage for that argument becomes absorption, and if it constrains it to be a function, the operand usage becomes inspection.

19.8.7.10 Streamability of Variable References

The sweep and posture of the variable reference V are the first of the following that apply:

  1. If all the following conditions are satisfied:

    1. V is a reference to a variable declared in a bind-group attribute of a containing xsl:for-each-group instruction F

    2. The path in the construct tree that connects V to the sequence constructor forming the body of F is such that no child construct is a higher-order operand of its parent

    3. The focus-setting container of V is F

    then the sweep and posture of V are the sweep and posture of the select expression of F.

  2. If all the following conditions are satisfied:

    1. V is a reference to a variable declared in a bind-group attribute of a containing xsl:merge instruction M

    2. The path in the construct tree that connects V to the sequence constructor forming the body of M is such that no child construct is a higher-order operand of its parent

    3. The focus-setting container of V is M

    then the sweep and posture of V are the sweep and posture of the sequence constructor contained in M.

  3. If all the following conditions are satisfied:

    1. V is a reference to a variable declared in a bind-source attribute of an xsl:merge-source child of a containing xsl:merge instruction M

    2. The path in the construct tree that connects V to the sequence constructor forming the body of M is such that no child construct is a higher-order operand of its parent

    3. The focus-setting container of V is M

    then the sweep and posture of V are the sweep and posture of the sequence constructor contained in M.

  4. Otherwise, V is roaming and free-ranging.

Note:

Informally, for streamed evaluation to be possible, a grouping variable reference must not appear in a construct that is evaluated repeatedly. For example, if $g is the variable bound to the current group, then the expression for $i in 1 to 10 return $g would not be streamable.

Otherwise, the sweep of the expression is motionless.

Note:

These rules reflect the fact that a node in a streamed document can never be bound to a variable, except in the case where it is part of the current group of nodes bound to a grouping variable.

19.8.7.11 Streamability of the Context Item Expression

The posture of the expression is the context posture, and the sweep is motionless.

Note:

Although . is intrinsically motionless, when used in certain contexts (such as data(.)) the containing expression will be consuming. This arises because of the operand usage: the argument to dataFO30 has usage absorption, and the combination of a motionless operand with usage absorption leads to the containing expression being consuming.

Similarly, if . is used where the operand usage is navigation, the containing expression will be free-ranging.

19.8.7.12 Streamability of Function Calls

For calls to built-in functions, see 19.8.8 Classifying Calls to Built-In Functions.

For a call to a constructor function, the 19.8.1 General Rules for Streamability apply. There is a single operand role (the argument to the function), with operand usage absorption.

For a call to a stylesheet function, the general streamability rules apply. There is one operand role for each argument in the function signature, and its operand usage is the type-determined usage based on the declared type of that argument.

If the function call is a partial function application (that is, one or more of the arguments is given as ?), then:

  1. If the function is focus-dependent, then the sweep is free-ranging

  2. Otherwise, the general streamability rules apply. The operands of a partial function application are the expressions actually supplied as arguments to the function, ignoring ? place-holders; the corresponding operand usage is the type-determined usage based on the declared type of that argument.

19.8.7.13 Streamability of Named Function References

A NamedFunctionRef is motionless, unless the function it refers to is focus-dependent, in which case it is free-ranging.

19.8.7.14 Streamability of Inline Function Declarations

The sweep of the expression is the first of the following that applies:

  1. If the body of the inline function contains a reference to a variable defined in the bind-group attribute of an xsl:for-each-group element external to the inline function, then free-ranging.

  2. Otherwise, motionless.

19.8.7.15 Streamability of map expressions

The posture and sweep of a map expression are the same as the posture and sweep of the equivalent xsl:map instruction. The equivalent xsl:map instruction is formed by creating a sequence of xsl:map-entry instructions, one for each key/value pair in the map expression, where the key expression becomes the value of xsl:map-entry/@key, and the value expression becomes the value of xsl:map-entry/@select; this sequence of xsl:map-entry instructions is then wrapped in an xsl:map parent instruction.

For example, the map expression map{'red':false(), 'green':true()} translates to the instruction:

<xsl:map>
  <xsl:map-entry key="'red'" select="false()"/>
  <xsl:map-entry key="'green'" select="true()"/>
</xsl:map>

The rules for the streamability of xsl:map appear in 19.8.4.22 Streamability of xsl:map.

See also 21.1.5 Maps and Streaming.

19.8.8 Classifying Calls to Built-In Functions

This section describes the rules that determine the streamability of calls to built-in functions. These differ from user-written functions because it is known (defined in the specification) how nodes supplied as operands are used. Knowledge of the usage of each operand, together with the posture of the actual operands, is in most cases enough to determine the posture and sweep of the function result.

All the built-in functions are listed below. For most functions, a simple proforma is shown that indicates the operand usage of each argument, using the code (A = absorption, I = inspection, T = transmission, N = navigation). So, for example, the entry fn:remove(T, A) means that for the function fn:remove#2, the operand usage of the first argument is transmission, and the operand usage of the second argument is absorption. By reference to the general rules in 19.8.1 General Rules for Streamability, this demonstrates that if the context posture is striding, the posture and sweep of the expression sum(remove(*,1)) will be grounded and consuming respectively.

For functions that default one of their arguments (typically to the context item), the relevant entry shows the equivalence, and the posture and sweep can in these cases be computed by filling in the default value for the relevant argument.

Some functions do not follow the general rules, and these are listed with a link to the section where the particular rules for that function are described.

  • fn:abs(A)

  • fn:accumulator-after – See 19.8.8.1 Streamability of the accumulator-after function

  • fn:accumulator-before – See 19.8.8.2 Streamability of the accumulator-before function

  • fn:adjust-date-to-timezone(A)

  • fn:adjust-date-to-timezone(A, A)

  • fn:adjust-dateTime-to-timezone(A)

  • fn:adjust-dateTime-to-timezone(A, A)

  • fn:adjust-time-to-timezone(A)

  • fn:adjust-time-to-timezone(A, A)

  • fn:analyze-string(A, A)

  • fn:analyze-string(A, A, A)

  • fn:available-environment-variables()

  • fn:avg(A)

  • fn:base-uri() – Equivalent to fn:base-uri(.)

  • fn:base-uri(I)

  • fn:boolean(I)

  • fn:ceiling(A)

  • fn:codepoint-equal(A, A)

  • fn:codepoints-to-string(A)

  • fn:collation-key(A)

  • fn:collation-key(A, A)

  • fn:collection()

  • fn:collection(A)

  • fn:compare(A, A)

  • fn:compare(A, A, A)

  • fn:concat(A, A, A)

  • fn:contains(A, A)

  • fn:contains(A, A, A)

  • fn:copy-of() – Equivalent to fn:copy-of(.)

  • fn:copy-of(A)

  • fn:count(I)

  • fn:current – See 19.8.8.3 Streamability of the current function

  • fn:current-date()

  • fn:current-dateTime()

  • fn:current-group – See 19.8.8.4 Streamability of the current-group function

  • fn:current-grouping-key – See 19.8.8.5 Streamability of the current-grouping-key function

  • fn:current-time()

  • fn:data() – Equivalent to fn:data(.)

  • fn:data(A)

  • fn:dateTime(A, A)

  • fn:day-from-date(A)

  • fn:day-from-dateTime(A)

  • fn:days-from-duration(A)

  • fn:deep-equal(A, A)

  • fn:deep-equal(A, A, A)

  • fn:deep-equal(A, A)

  • fn:deep-equal(A, A, A)

  • fn:default-collation()

  • fn:distinct-values(A)

  • fn:distinct-values(A, A)

  • fn:doc(A)

  • fn:doc-available(A)

  • fn:document(A)

  • fn:document(A, I)

  • fn:document-uri() – Equivalent to fn:document-uri(.)

  • fn:document-uri(I)

  • fn:element-available(A)

  • fn:element-with-id(x) – Equivalent to fn:element-with-id(x, .)

  • fn:element-with-id(A, N)

  • fn:empty(I)

  • fn:encode-for-uri(A)

  • fn:ends-with(A, A)

  • fn:ends-with(A, A, A)

  • fn:environment-variable(A)

  • fn:error()

  • fn:error(A)

  • fn:error(A, A)

  • fn:error(A, A, N)

  • fn:escape-html-uri(A)

  • fn:exactly-one(T)

  • fn:exists(I)

  • fn:false()

  • fn:filter(N, I)

  • fn:floor(A)

  • fn:fold-left(N, A, I)

  • fn:fold-right(N, A, I)

  • fn:for-each(N, I)

  • fn:for-each-pair(N, N, I)

  • fn:format-date(A, A)

  • fn:format-date(A, A, A, A, A)

  • fn:format-dateTime(A, A)

  • fn:format-dateTime(A, A, A, A, A)

  • fn:format-integer(A, A)

  • fn:format-integer(A, A, A)

  • fn:format-number(A, A)

  • fn:format-number(A, A, A)

  • fn:format-time(A, A)

  • fn:format-time(A, A, A, A, A)

  • fn:function-arity(A)

  • fn:function-available(A)

  • fn:function-available(A, A)

  • fn:function-lookup – See 19.8.8.6 Streamability of the function-lookup function

  • fn:function-name(A)

  • fn:generate-id() – Equivalent to fn:generate-id(.)

  • fn:generate-id(I)

  • fn:has-children() – Equivalent to fn:has-children(.)

  • fn:has-children(I)

  • fn:head(T)

  • fn:hours-from-dateTime(A)

  • fn:hours-from-duration(A)

  • fn:hours-from-time(A)

  • fn:id(x) – Equivalent to fn:id(x, .)

  • fn:id(A, N)

  • fn:idref(x) – Equivalent to fn:idref(x, .)

  • fn:idref(A, N)

  • fn:implicit-timezone()

  • fn:in-scope-prefixes(I)

  • fn:index-of(A, A)

  • fn:index-of(A, A, A)

  • fn:innermost(N)

  • fn:insert-before(T, A, T)

  • fn:iri-to-uri(A)

  • fn:json-to-xml(A)

  • fn:json-to-xml(A, A)

  • fn:key(x, x) – Equivalent to fn:key(x, x, /)

  • fn:key(A, A, N)

  • fn:lang(x) – Equivalent to fn:lang(x, .)

  • fn:lang(A, I)

  • fn:last – See 19.8.8.7 Streamability of the last function

  • fn:local-name() – Equivalent to fn:local-name(.)

  • fn:local-name(I)

  • fn:local-name-from-QName(A)

  • fn:lower-case(A)

  • fn:matches(A, A)

  • fn:matches(A, A, A)

  • fn:max(A)

  • fn:max(A, A)

  • fn:min(A)

  • fn:min(A, A)

  • fn:minutes-from-dateTime(A)

  • fn:minutes-from-duration(A)

  • fn:minutes-from-time(A)

  • fn:month-from-date(A)

  • fn:month-from-dateTime(A)

  • fn:months-from-duration(A)

  • fn:name() – Equivalent to fn:name(.)

  • fn:name(I)

  • fn:namespace-uri() – Equivalent to fn:namespace-uri(.)

  • fn:namespace-uri(I)

  • fn:namespace-uri-for-prefix(A, I)

  • fn:namespace-uri-from-QName(A)

  • fn:nilled() – Equivalent to fn:nilled(.)

  • fn:nilled(I)

  • fn:node-name() – Equivalent to fn:node-name(.)

  • fn:node-name(I)

  • fn:normalize-space()

  • fn:normalize-space(A)

  • fn:normalize-unicode(A)

  • fn:normalize-unicode(A, A)

  • fn:not(I)

  • fn:number() – Equivalent to fn:number(.)

  • fn:number(A)

  • fn:one-or-more(T)

  • fn:outermost – See 19.8.8.8 Streamability of the outermost function

  • fn:parse-xml(A)

  • fn:parse-xml-fragment(A)

  • fn:path() – Equivalent to fn:path(.)

  • fn:path(N)

  • fn:position – See 19.8.8.9 Streamability of the position function

  • fn:prefix-from-QName(A)

  • fn:QName(A, A)

  • fn:regex-group(A)

  • fn:remove(T, A)

  • fn:replace(A, A, A)

  • fn:replace(A, A, A, A)

  • fn:resolve-QName(A, I)

  • fn:resolve-uri(A)

  • fn:resolve-uri(A, A)

  • fn:reverse(N)

  • fn:root – See 19.8.8.10 Streamability of the root function

  • fn:round(A)

  • fn:round(A, A)

  • fn:round-half-to-even(A)

  • fn:round-half-to-even(A, A)

  • fn:seconds-from-dateTime(A)

  • fn:seconds-from-duration(A)

  • fn:seconds-from-time(A)

  • fn:serialize(A)

  • fn:serialize(A, A)

  • fn:serialize-json(A)

  • fn:serialize-json(A, A)

  • fn:snapshot() – Equivalent to fn:snapshot(.)

  • fn:snapshot(A)

  • fn:starts-with(A, A)

  • fn:starts-with(A, A, A)

  • fn:static-base-uri()

  • fn:string() – Equivalent to fn:string(.)

  • fn:string(A)

  • fn:string-join(A)

  • fn:string-join(A, A)

  • fn:string-length() – Equivalent to fn:string-length(.)

  • fn:string-length(A)

  • fn:string-to-codepoints(A)

  • fn:subsequence(T, A)

  • fn:subsequence(T, A, A)

  • fn:substring(A, A)

  • fn:substring(A, A, A)

  • fn:substring-after(A, A)

  • fn:substring-after(A, A, A)

  • fn:substring-before(A, A)

  • fn:substring-before(A, A, A)

  • fn:sum(A)

  • fn:sum(A, A)

  • fn:system-property(A)

  • fn:tail(T)

  • fn:timezone-from-date(A)

  • fn:timezone-from-dateTime(A)

  • fn:timezone-from-time(A)

  • fn:tokenize(A, A)

  • fn:tokenize(A, A, A)

  • fn:trace(A, A)

  • fn:translate(A, A, A)

  • fn:true()

  • fn:type-available(A)

  • fn:unordered(T)

  • fn:unparsed-entity-public-id – See 19.8.8.11 Streamability of the unparsed-entity-public-id function

  • fn:unparsed-entity-uri – See 19.8.8.12 Streamability of the unparsed-entity-uri function

  • fn:unparsed-text(A)

  • fn:unparsed-text(A, A)

  • fn:unparsed-text-available(A)

  • fn:unparsed-text-available(A, A)

  • fn:unparsed-text-lines(A)

  • fn:unparsed-text-lines(A, A)

  • fn:upper-case(A)

  • fn:uri-collection()

  • fn:uri-collection(A)

  • fn:year-from-date(A)

  • fn:year-from-dateTime(A)

  • fn:years-from-duration(A)

  • fn:zero-or-one(T)

  • map:contains(A, A)

  • map:entry(A, N)

  • map:for-each-entry(A, A)

  • map:get(A, A)

  • map:keys(A)

  • map:new()

  • map:new(A)

  • map:remove(A, A)

  • map:size(A)

  • map:size(A)

  • math:acos(A)

  • math:asin(A)

  • math:atan(A)

  • math:atan2(A, A)

  • math:cos(A)

  • math:exp(A)

  • math:exp10(A)

  • math:log(A)

  • math:log10(A)

  • math:pi()

  • math:pow(A, A)

  • math:sin(A)

  • math:sqrt(A)

  • math:tan(A)

19.8.8.1 Streamability of the accumulator-after function

See 18.2.7 Streamability of Accumulators.

To ensure that the supplied value for the first argument (the accumulator name) is not dependent on the streamed input document, its operand usage is classified as navigation.

The posture and sweep of the function call then follow the general streamability rules.

19.8.8.2 Streamability of the accumulator-before function

See 18.2.7 Streamability of Accumulators.

To ensure that the supplied value for the first argument (the accumulator name) is not dependent on the streamed input document, its operand usage is classified as navigation.

The posture and sweep of the function call then follow the general streamability rules.

19.8.8.3 Streamability of the current function

The sweep of the function is motionless; the posture is the context posture for evaluation of the outermost containing XPath expression (that is, the context posture that would obtain if the entire XPath expression were replaced with ".").

Note:

Although the current is supported for streaming, it needs to be used with care. Some common use cases such as select="$lookup[@name = current()/name] will fail, because the streamability rules require a predicate to be motionless. A workaround is to extract the relevant value into a variable: select="let $n := string(name) return $lookup[@name = $n]; in turn this removes the need for the current function.

The use of current within a pattern is supported with similar restrictions. In this case the context posture is always striding.

19.8.8.4 Streamability of the current-group function

XSLT 3.0 introduces the bind-group attribute on the xsl:for-each-group instruction to enable grouping code to be statically analyzed for streamability. Use of the current-group and current-grouping-key functions is therefore incompatible with streaming.

Specifically: a call on the current-group is roaming and free-ranging.

19.8.8.6 Streamability of the function-lookup function

See 10.3.5 Dynamic Access to Functions for special rules that relate to streamability of calls to the function-lookupFO30 function.

With the caveats given there, the function follows the general streamability rules, for a function with two arguments that both have operand usage absorption.

19.8.8.7 Streamability of the last function

If the context posture for a call on the lastFO30 function is striding, crawling, or roaming, then the posture of the function is roaming, and the sweep is free-ranging.

In all other cases the function is grounded and motionless.

Note:

The cases where lastFO30 can be used without affecting streamability are where the context item is either grounded or climbing. The latter condition makes expressions like ancestor::*[@xml:space][last()] streamable.

There are special rules restricting the use of lastFO30 in the predicate of a pattern: see 19.8.9 Classifying Patterns.

19.8.8.8 Streamability of the outermost function

The single argument to this function has operand usage transmission.

The streamability of the function call follows the general streamability rules with one exception: if the posture of the argument is crawling, then the posture of the result is striding.

Note:

There are cases where the streaming rules allow the construct outermost(//para) but do not allow //para; the function can therefore be useful in cases where it is known that para elements will not be nested, as well as cases where the application actually wishes to process all para elements except those that are nested within another.

By contrast, the innermostFO30 function offers no streaming benefits. Although it delivers a subset of the input nodes as its result, in the correct order, it is classed as navigational because it needs to look aread in the input stream before deciding whether a node can be included in the result.

19.8.8.9 Streamability of the position function

The positionFO30 function follows the general streamability rules. Since it has no operands, this means it is grounded and motionless.

Note:

Within an expression, there are no special difficulties in evaluating the positionFO30 function.

It does have special treatment within a predicate of a pattern, however: a pattern is not motionless if it contains a call to positionFO30, as explained in 19.8.9 Classifying Patterns.

19.8.8.10 Streamability of the root function

The zero-argument function root() is equivalent to root(.).

Given the expression root(X), if the item type of X is document-node(), or a subtype thereof, and if its posture is striding, then root(X) is rewritten as X. Otherwise, it is rewritten as head((X)/ancestor-or-self::node()). Streamability analysis is then applied to the rewritten expression.

Note:

Because path expressions starting with / are rewritten to use the rootFO30 function, this ensures that a leading slash is ignored if the context item is a document node, for example within a template rule with match="/". This improves streamability, because upwards navigation followed by downward navigation is disallowed.

19.8.8.11 Streamability of the unparsed-entity-public-id function

The function unparsed-entity-public-id has an implicit dependency on the context item.

If the context item type is anything other than a document node, the function works without difficulty in streaming mode: in the same way as attributes of ancestor elements are retained and are available while processing descendant elements, the unparsed entities declared in the DTD are retained while processing the body of the document.

While processing the document node itself, however, the contents of the DTD might not yet be available. An arbitrary number of comments and processing instructions are allowed to precede the DTD.

So the rules are:

  • If the context posture is grounded, the posture is grounded and the sweep is motionless

  • If the context posture is roaming, the posture is roaming and the sweep is free-ranging

  • If the context posture is climbing, striding, or crawling, the context item type permits a document node, then the posture is crawling and the sweep is consuming

  • If the context posture is climbing, striding, or crawling, the context item type does not permit a document node, then the posture is grounded and the sweep is motionless

19.8.8.12 Streamability of the unparsed-entity-uri function

The streamability characteristics of this function are the same as unparsed-entity-public-id: see 19.8.8.11 Streamability of the unparsed-entity-public-id function.

19.8.9 Classifying Patterns

Note:

Patterns differ from other kinds of construct in that they are not composable in the same way. It is best to think of a pattern as specialized syntax for a function that takes an item as its argument and returns a boolean: true if the pattern matches the item, otherwise false. When we refer to the type of a pattern, however, this refers to the types of item that the pattern is capable of matching, not to the type of value that evaluation of the pattern returns.

The sweep of a pattern is either motionless or free-ranging. (Although there are patterns that could in principle be evaluated by consuming the element node that they match, these are of no interest in the analysis, so they are classified as free-ranging.)

The posture of a pattern is grounded if the pattern is motionless, or roaming otherwise. (This reflects the fact that a pattern always returns a boolean result; it never returns a node in a streamed document.)

Informally, a motionless pattern is one that can be evaluated by a streaming processor when the input stream is positioned at the start of the node being matched, without advancing the input stream.

A pattern is motionless if and only if it satisfies all the following conditions:

  1. The pattern does not contain a RootedPath.

  2. If the pattern contains predicates, then every top-level Predicate in the pattern satisfies both the following conditions:

    1. The expression immediately contained in the predicate is motionless, when assessed with a context posture of striding, and a context item type set to the static type of the expression to which the predicate applies, determined using the rules in 19.2 Determining the Static Type of a Construct.

    2. The predicate is a non-positional predicate.

    The use of the term top-level in this rule means that predicates that are nested within other predicates do not themselves have to be non-positional, though they may play a role in the analysis of top-level predicates.

  3. The pattern does not contain (at any depth) a variable reference bound to a variable declared in the bind-group attribute of an xsl:for-each-group instruction.

[Definition: A predicate is a non-positional predicate if it satisfies both of the following conditions:]

  1. The predicate does not contain a function call or named function reference to any of the following functions, unless that call or reference occurs within a nested predicate:

    1. positionFO30

    2. lastFO30

    3. function-lookupFO30.

    Note:

    The exception for nested predicates is to avoid disqualifying patterns such as match="p[@code = $status[last()]].

  2. The expression immediately contained in the predicate is a non-numeric expression. An expression is non-numeric if its static item type (see 19.2 Determining the Static Type of a Construct) S has the property that there is no SequenceType T (other than xs:error) such that subtype(T, S) and (subtype(T, xs:decimal) or subtype(T, xs:double) or subtype(T, xs:float)). The subtype relation is defined in Section 2.5.6.1 The judgement subtype(A, B) XP30

Note:

A non-positional predicate can be evaluated by considering each item in the filtered sequence independently; the result never depends on the position of other items in the sequence or the length of the sequence.

A pattern that is not motionless is classified as free-ranging.

The following list shows examples of motionless patterns:

  • /

  • *

  • /*

  • p

  • p|q

  • p/q

  • p[@status='red']

  • p[base-uri()]

  • p[@class or @style]

  • p[@status]

  • p[@status = $status-codes[1]]

  • p[@class | @style]

  • p[contains(@class, ':')]

  • p[substring-after(@class, ':')]

  • p[ancestor::*[@xml:lang]]

  • text()[starts-with(., '$')]

  • @price

  • @price[starts-with(., '$')]

  • //p/text()[. = 'Introduction']

The following list shows examples of patterns that are not motionless, explaining why not:

  • id('abc') (contains a RootedPath)

  • $doc//p (contains a RootedPath)

  • p[b] (the predicate is not motionless)

  • p[. = 'Introduction'] (the predicate is not motionless)

  • p[starts-with(., '$')] (the predicate is not motionless)

  • p[preceding-sibling::p[1] = ''] (the predicate is not motionless)

  • p[1] (contains a positional predicate: return type is numeric)

  • p[$pnum + 1] (contains a positional predicate: return type is numeric)

  • p[data(@status)] (contains a positional predicate: return type is potentially numeric)

  • p[position() gt 2] (contains a positional predicate: calls position())

  • p[last()] (contains a positional predicate: calls last())

19.9 Examples of Streamability Analysis

The examples in this section are intended to illustrate how the streamability rules are applied "top down" to establish whether template rules are guaranteed streamable.

Example: A recursive-descent template rule

Consider the following template rule, where mode s is defined with streamable="yes":

<xsl:template match="para" mode="s">
  <div class="para">
    <xsl:apply-templates mode="s"/>
  </div>
</xsl:template>

The processor is required to establish that this template meets the streamability rules. Specifically, as stated in 6.6.3 Streamable Templates, it must satisfy three conditions:

  1. The match pattern must be motionless.

  2. The body of the template rule must be grounded.

  3. The initializers of any template parameters must be motionless.

The third condition is satisfied trivially because there are no parameters.

The first rule depends on the rules for assessing patterns, which are given in 19.8.9 Classifying Patterns. This pattern is motionless because (a) it does not contain a RootedPath, and (b) it contains no predicates.

So it remains to determine that the body of the template is grounded. The proof of this is as follows:

  1. The sequence constructor forming the body of the template is assessed according to the rules in 19.8.3 Classifying Sequence Constructors, which tell us that there is a single operand (the <div> literal result element) which has operand usage U = transmission.

  2. The assessment of the sequence constructor uses the general streamability rules. These rules require us to determine the type T, sweep S, posture P, and usage U of each operand. We have already established that there is a single operand, with U = transmission. Section 19.2 Determining the Static Type of a Construct tells us that for all instructions, we can take T = item(). The posture P and sweep S of the literal result element are established as follows:

    1. The rules for literal result elements (specifically the <div> element) are given in 19.8.4.1 Streamability of Literal Result Elements. This particular literal result element has only one operand (its contained sequence constructor), with operand usage U = absorption.

    2. The general streamability rules again apply. Again the static type T of the operand is item(), and we need to determine the posture P and sweep S.

    3. To determine the posture and sweep of this sequence constructor (the one that contains the xsl:apply-templates instruction) we refer again to the general streamability rules.

      1. The sequence constructor has a single operand (the xsl:apply-templates instruction); again U = transmission, T = item().

      2. The posture P and sweep S of the xsl:apply-templates instruction are established as follows:

        1. The rules that apply are in 19.8.4.5 Streamability of xsl:apply-templates.

        2. Rule 1 does not apply because the select expression (which defaults to child::node()) is not grounded. This is a consequence of the rules in 19.8.7.7 Streamability of Axis Steps, specifically:

          1. The context posture of the axis step is established by the template rule as a whole, as striding.

          2. Therefore rules 1 and 2 do not apply.

          3. The statically-inferred context item type is derived from the match pattern (match="para"). This gives a type of element(). The child axis for element nodes is not necessarily empty, so rule 3 does not apply.

          4. Rule 4 does not apply because there are no predicates.

          5. So the posture and sweep of the axis step child::node() are given by the table in rule 5. The entry for (context posture = striding, axis = child) gives a posture of striding and a sweep of consuming.

          6. So the select expression is not grounded. (The same result can be reached intuitively: an expression that selects streamed nodes will never be grounded.)

        3. Rule 2 does not apply because there is no xsl:sort element.

        4. Rule 3 does not apply because the mode is declared with streamable="yes".

        5. So the posture P and sweep S of the xsl:apply-templates instruction are established by the general streamability rules, as follows:

          1. There is a single operand, the implicit select="child::node()" expression, with usage U = absorption.

          2. We have already established that for this operand, the posture P = striding and the sweep S = consuming.

          3. By the rules in 19.2 Determining the Static Type of a Construct, the type T of the select expression is node().

          4. In the general streamability rules, the adjusted sweep S' for an operand with (P = striding, U = absorption) is consuming,

          5. Rule 2(d) then applies, so the xsl:apply-templates instruction is consuming and grounded.

      3. So the sequence constructor that contains the xsl:apply-templates instruction has one operand with U = transmission, T = item(), P = grounded, S = consuming. Rule 2(d) of the general streamability rules applies, so the sequence constructor itself has P = grounded, S = consuming.

    4. So the literal result element has one operand with U = absorption, T = item(), P = grounded, S = consuming. Rule 2(d) of the general streamability rules applies, so the literal result element has P = grounded, S = consuming.

  3. So the sequence constructor containing the literal result element has one operand with U = transmission, T = item(), P = grounded, S = consuming. Rule 2(d) of the general streamability rules applies, so this sequence constructor itself has P = grounded, S = consuming.

  4. So we have established that the sequence constructor forming the body of the template rule is grounded.

Therefore, since the other conditions are also satisfied, the template is guaranteed-streamable.

The analysis presented above could have been simplified by taking into account the fact that the streamability properties of a sequence constructor containing a single instruction are identical to the properties of that instruction. This simplification will be exploited in the next example.

 

Example: An aggregating template rule

Consider the following template rule, where mode s is defined with streamable="yes":

<xsl:template match="transactions[@currency='USD']" mode="s">
  <total><xsl:value-of select="sum(transaction/@value)"/></total>
</xsl:template>

Again, as stated in 6.6.3 Streamable Templates, it must satisfy three conditions:

  1. The match pattern must be motionless.

  2. The body of the template rule must be grounded.

  3. The initializers of any template parameters must be motionless.

The third condition is satisfied trivially because there are no parameters.

The first rule depends on the rules for assessing patterns, which are given in 19.8.9 Classifying Patterns. This pattern is motionless because (a) it is not a RootedPath, and (b) every predicate is motionless and non-positional. The analysis that proves the predicate is motionless and non-positional proceeds as follows:

  1. First establish that that the expression @currency='USD' is motionless, as follows:

    1. The predicate is a general comparison (GeneralComp) which follows the general streamability rules.

    2. There are two operands: a ForwardsAxisStep and a Literal. Both operand roles are absorption.

    3. The first operand has type T = attribute(). Its posture and sweep are determined by the rules in 19.8.7.7 Streamability of Axis Steps. The context posture is striding, so the posture and sweep are determined by the entry in the table (rule 5) with context posture = striding, axis = attribute: that is, the result posture is climbing and the sweep is motionless.

    4. The second operand, being a literal, is grounded and motionless.

    5. In the general streamability rules, rule 2(e) applies, so the predicate is grounded and motionless

  2. Now establish that that the expression @currency='USD' is non-positional, as follows:

    1. Rule 1 is satisfied: the predicate does not call positionFO30, lastFO30, or function-lookupFO30.

    2. Rule 2 is satisfied: the expression @currency='USD' is non-numeric. The static type of the expression is determined using the rules in 19.2 Determining the Static Type of a Construct as xs:boolean, and this has no common subtypes with xs:decimal, xs:double, or xs:float.

So both conditions in 19.8.9 Classifying Patterns are satisfied, and the pattern is therefore motionless.

It remains to show that the body of the template rule is grounded. The proof of this is as follows. Unlike the previous example, the analysis is shown in simplified form; in particular the two sequence constructors which each contain a single instruction are ignored, and replaced in the construct tree by their contained instruction.

  1. We need to show that the <total> literal result element is grounded.

  2. The rules that apply are in 19.8.4.1 Streamability of Literal Result Elements.

  3. These rules refer to the general streamability rules. There is one operand, the xsl:value-of child element, which has operand usage U = absorption, and type T = item().

  4. So we need to determine the posture and sweep of the xsl:value-of instruction.

    1. The rules are given in 19.8.4.37 Streamability of xsl:value-of.

    2. The general streamability rules apply. There is one operand, the expression sum(transaction/@value), which has operand usage U = absorption.

    3. The type T of this operand is the return type defined in the signature of the sumFO30 function, that is, xs:anyAtomicType.

    4. The posture P and sweep S are established as follows:

      1. The rules that apply to the call on sumFO30 are given in 19.8.8 Classifying Calls to Built-In Functions.

      2. The relevant proforma is fn:sum(A), indicating that the general streamability rules apply, and that there is a single operand with usage U = absorption.

      3. The type T of the operand transaction/@value is determined (by the rules in 19.2 Determining the Static Type of a Construct) as attribute().

      4. The posture P and sweep S of the operand transaction/@value are determined by the rules in 19.8.7.6 Streamability of Path Expressions, as follows:

        1. The expression is expanded to child::transaction/attribute::value.

        2. The posture and sweep of the first operand child::transaction are determined by the rules in 19.8.7.7 Streamability of Axis Steps, as follows:

          1. The context posture is striding, because the focus-setting container is the template rule itself.

          2. The context item type is element(), based on the match type of the pattern match="transactions[@currency='USD']".

          3. Rules 1 and 2 do not apply because the context posture is striding.

          4. Rule 3 does not apply because the child axis applied to an element node is not necessarily empty.

          5. Rule 4 does not apply because there are no predicates.

          6. Rule 5 applies, and the table entry with context posture = striding, axis = child gives a result posture of striding and a sweep of consuming.

        3. The posture of the relative path expression child::transaction/attribute::value is therefore the posture of its second operand attribute::value, assessed with a context posture of striding. This is determined by the rules in 19.8.7.7 Streamability of Axis Steps, as follows:

          1. The context posture, as we have seen, is striding.

          2. The context item type is element(), based on the type of the first operand child::transaction.

          3. Rules 1 and 2 do not apply because the context posture is striding.

          4. Rule 3 does not apply because the attribute axis applied to an element node is not necessarily empty.

          5. Rule 4 does not apply because there are no predicates.

          6. Rule 5 applies, and the table entry with context posture = striding, axis = attribute gives a result posture of climbing and a sweep of motionless.

        4. The posture of the relative path expression child::transaction/attribute::value is therefore climbing.

        5. The sweep of the relative path expression child::transaction/attribute::value is the wider of the sweeps of its two operands, namely consuming and motionless. That is, it is consuming.

      5. So the first and only operand to the call on sum() has U = absorption, T = attribute(), P = climbing, and S = consuming

      6. Rule 1(b) of the general streamability rules computes the adjusted sweep S'. Rule 1(b)(iii)(A) applies, so the effective operand usage U' is inspection. Rule 1(b)(iii)(A) then computes the adjusted sweep from the table entry for P = climbing, U' = inspection; this shows S' = S, that is, consuming.

      7. Rule 2(d) now applies, so the call on sum() is grounded and consuming.

    5. Since the xsl:value-of instruction has one operand with U = absorption, T = xs:anyAtomicType, P = grounded, and S = consuming, rule 2(d) again applies, and the xsl:value-of instruction is grounded and consuming.

  5. Since the literal result element has one operand with U = absorption, T = item(), P = grounded, and S = consuming, rule 2(d) again applies, and the literal result element is grounded and consuming.

  6. Therefore the body of the template rule is grounded, and since the other conditions are also satisfied, it is guaranteed-streamable.

 

Example: Streamed Grouping

Consider the following code, which is designed to process a transaction file containing transactions in chronological order, and output the total value of the transactions for each day.

<xsl:template name="go">
  <out>
    <xsl:stream href="transactions.xml">
      <xsl:for-each-group select="/account/transaction" 
                          group-adjacent="xs:date(@timestamp)" 
                          bind-group="g" bind-grouping-key="k">
         <total date="{$k}" value="{sum($g/@value)}"/>
      </xsl:for-each-group>
    </xsl:stream>
  </out>
</xsl:template>

The rules for xsl:stream say that the instruction is guaranteed-streamable if the contained sequence constructor is grounded, and the task of streamability analysis is to prove that this is the case. As in the previous example, we will take a short-cut by making the assumption that a sequence constructor containing a single instruction can be replaced by that instruction in the construct tree.

So the task is to show that the xsl:for-each-group instruction is grounded, which we can do as follows:

  1. The relevant rules are to be found in 19.8.4.18 Streamability of xsl:for-each-group.

  2. Rule 1 applies only if the select expression is grounded. It is easy to see informally that this is not the case (an expression that returns streamed nodes is never grounded). More formally:

    1. The select expression is a path expression; the rules in 19.8.7.6 Streamability of Path Expressions apply.

    2. The expression is rewritten as ((root(.) treat as document-node())/child::account)/child::transaction

    3. The left-hand operand (root(.) treat as document-node())/child::account is also a path expression, so the rules in 19.8.7.6 Streamability of Path Expressions apply recursively:

      1. The left-hand operand root(.) treat as document-node() follows the rules for a TreatExpr in 19.8.7 Classifying Expressions; the proforma T treat as TYPE indicates that the general streamability rules apply with a single operand having usage transmission.

      2. This single operand root(.) follows the rules in 19.8.8.10 Streamability of the root function. The item type of the operand . is the context item type, which is the type established by the xsl:stream instruction, namely document-node(). Under these conditions root(.) is rewritten as ., so the posture is the context posture establised by the xsl:stream instruction, namely striding. The sweep is motionless.

      3. The posture and sweep of the expression root(.) treat as document-node() are the same as the posture and sweep of root(.), namely striding and motionless

      4. The right-hand operand child::account is governed by the rules in 19.8.7.7 Streamability of Axis Steps. The context posture is striding, and the axis is child, so the result posture is striding and the sweep is consuming.

      5. The posture of the path expression is the posture of the right-hand operand, that is striding, and its sweep is the wider sweep of the two operands, that is consuming

    4. Returning to the outer path expression, the posture of the right hand operand child::transaction is striding, and its sweep is consuming.

    5. So the posture of the select expression as a whole is the posture of the right hand operand, that is striding; and its sweep is the wider of the sweeps of the operands, which is consuming.

  3. Rule 2 does not apply: there is no group-by attribute.

  4. Rule 3 does not apply: there is a group-adjacent attribute, but it is motionless. The reasoning is as follows:

    1. The value is a call to the constructor function xs:date. The rules in 19.8.7.12 Streamability of Function Calls apply. There is a single operand, whose required type is atomic, so the operand usage is absorption.

    2. These rules refer to the general streamability rules, so we need to determine the context item type, posture, and sweep of the operand expression @timestamp. This is done as follows:

      1. The expression is an AxisStep, so the relevant rules are in 19.8.7.7 Streamability of Axis Steps.

      2. The context posture is the posture of the controlling operand of the focus-setting container, that is, is the select expression of the containing xsl:for-each-group instruction, which as established above is striding. The context item type is similarly the inferred type of the select expression, and is element().

      3. Rules 1 and 2 do not apply because the context posture is striding.

      4. Rule 3 does not apply because the attribute axis for an element node is not necessarily empty.

      5. Rule 4 does not apply because there is no predicate.

      6. So the sweep and posture of the expression @timestamp are given by the table in Rule 5 as climbing and motionless.

    3. Returning to the general streamability rules for the expression xs:date(@timestamp), the first operand has U = absorption, T = attribute(), P = climbing, S = motionless.

    4. Under Rule 1(b)(iii)(A), because T = attribute(), the operand usage U' becomes inspection.

    5. Under Rule 1(b)(iii)(A), S' = S = motionless.

    6. Under Rule 2(e), the expression xs:date(@timestamp) is grounded and motionless.

  5. Rule 4 (under xsl:for-each-group) does not apply, because there is no group-starting-with or group-ending-with attribute.

  6. Rule 5 does not apply, because there is no xsl:sort child.

  7. Rule 6 does not apply, because there is a bind-group attribute.

  8. Rule 7 does not apply, because both group-adjacent and bind-grouping-key are present.

  9. So Rule 8 applies. This relies on knowing the posture of the sequence constructor containined in the xsl:for-each-group instruction: that is, the posture of the total literal result element. This is calculated as follows:

    1. The rules that apply are in 19.8.4.1 Streamability of Literal Result Elements. The general streamability rules apply; there are two operands, the attribute value templates {$k} and {sum($g/@value}, and in each case the usage is absorption. We can simplify the analysis by observing that that the empty sequence constructor contained in the literal result element can be ignored, since it is grounded and motionless.

    2. Consider first the operand {$k}.

      1. Section 19.8.6 Classifying Value Templates applies. This refers to the general streamability rules; there is a single operand, the expression $k, with usage absorption.

      2. The rules for the expression $k are given in 19.8.7.10 Streamability of Variable References. These establish that the expression is grounded and motionless.

      3. It follows that the operand {$k} expression is also grounded and motionless.

    3. Now consider the operand {sum($g/@value)}.

    4. Section 19.8.6 Classifying Value Templates applies. This refers to the general streamability rules; there is a single operand, the expression sum($g/@value), with usage absorption.

    5. The rules for the sum function appear in 19.8.8 Classifying Calls to Built-In Functions. The proforma is given there as fn:sum(A), which means that the general streamability rules apply, and that the single operand $g/@value has usage absorption. So we need to establish the posture, sweep, and type of this expression, which we can do as follows:

      1. The expression is a RelativePathExpr, so section 19.8.7.6 Streamability of Path Expressions applies.

      2. The expression is expanded to $g/attribute::value.

      3. The posture and sweep of the left-hand operand $g are defined in 19.8.7.10 Streamability of Variable References, which has special rules for a variable bound in the bind-group attribute of a containing xsl:for-each-group instruction. Specifically, the posture of $g is the posture of the select expression, that is striding, and its sweep is the sweep of the select expression, that is consuming.

      4. The posture and sweep of the right hand operand @value are defined in 19.8.7.7 Streamability of Axis Steps. The context posture is the posture of the left-hand operand $g, namely striding; the table in Rule 5 applies, giving the result climbing and motionless

      5. The posture of the RelativePathExpr is the posture of the right hand operand, namely climbing. The sweep of the RelativePathExpr is the wider of the sweeps of its operands, which is consuming

      6. The type of the expression $g/@value is determined using the rules in 19.2 Determining the Static Type of a Construct as attribute().

    6. So the sum function has a single operand with U = absorption, P = climbing, S = consuming, T = attribute().

    7. In the general streamability rules, Rule 1(b)(iii)(A) gives the adjusted usage as U' = inspection, and Rule 1(b)(iii)(B) gives the adjusted sweep as S' = S = consuming. Rule 2(d) gives the posture and sweep of the call to sum as grounded and consuming.

  10. So the literal result element has two operands, one of which is grounded and motionless, the other grounded and consuming. Rule 2(d) of the general streamability rules determines that the literal result element is grounded and consuming.

  11. So the content of the xsl:stream instruction is grounded, which means that the instruction is guaranteed-streamable.

19.10 Streamability Guarantees

Certain constructs allow a stylesheet author to declare that a construct is streamable. Specifically:

  1. Specifying streamable="yes" on xsl:mode declares that all template rules in that mode (and all template rules that specify mode="#all") are streamable;

  2. The xsl:stream instruction implicitly declares that its contained sequence constructor is streamable;

  3. Specifying streamable="yes" on xsl:attribute-set declares that the attribute set in question is streamable;

  4. Specifying streamable="yes" on xsl:merge declares that the merging process is streamable.

  5. Specifying streamable="yes" on xsl:accumulator declares that the accumulator can be evaluated on a streamed document.

In each case the construct in question is said to be guaranteed-streamable if it satisfies two conditions:

  1. Streamability is declared by specifying streamable="yes".

  2. Streamability analysis following the rules defined in this specification determines that streamed processing is possible (the detailed conditions vary from one construct to another).

[Definition: A guaranteed-streamable construct is a construct that is declared to be streamable and that follows the particular rules for that construct to make streaming possible, as defined by the analysis in this specification.]

For a streaming processor, that is, a processor that claims conformance with the streaming feature:

  1. If a construct is guaranteed-streamable then it must be processed using streaming.

  2. If a construct is declared as streamable but is not guaranteed-streamable (that is, if it fails to satisfy the conditions for streamability defined in this specification), then the processor must be prepared to do any one of the following at user option:

    1. Signal a static error [see ERR XTSE3430]

    2. Process the stylesheet as if it were a non-streaming processor (see below)

    3. Process the stylesheet with streaming if it is able to do so, or signal a static error [see ERR XTSE3430] if it is not able to do so.

[ERR XTSE3430] It is a static error if the stylesheet contains a construct that is declared to be streamable but which is not guaranteed-streamable, unless the user has indicated that the processor is to handle this situation by processing the stylesheet without streaming or by making use of processor extensions to the streamability rules where available.

For a non-streaming processor, the processor must evaluate the construct delivering the same results as if execution used streaming, but with no constraints on the evaluation strategy. (Processing may, of course, fail due to insufficient memory being available, or for other reasons.)

Note:

This specification does not attempt to legislate precisely what constitutes evaluation "using streaming". The most important test is that the amount of memory needed should be for practical purposes independent of the size of the source document, and in particular that the finite size of memory available should not impose a limit on the size of source document that can be processed.

The rules are designed to ensure that streaming processors can analyze streamability using rules different from those in this specification, provided that all constructs that are guaranteed-streamable according to this specification are actually streamable by the implementation. Furthermore, non-streaming processors are not required to analyze streamability at all.

20 Additional Functions

This section describes XSLT-specific additions to the core function library. Some of these additional functions also make use of information specified by declarations in the stylesheet; this section also describes these declarations.

20.1 fn:document

Summary

Provides access to XML documents identified by a URI.

Signatures

document($uri-sequence as item()*) as node()*
document( $uri-sequence  as item()*,
$base-node  as node()) as node()*
Properties

The one-argument form of this function is deterministicFO30, focus-independentFO30, and context-dependentFO30. It depends on static base uri.

The two-argument form of this function is deterministicFO30, focus-independentFO30, and context-independentFO30.

Rules

The document function allows access to XML documents identified by a URI.

The first argument contains a sequence of URI references. The second argument, if present, is a node whose base URI is used to resolve any relative URI references contained in the first argument.

A sequence of absolute URI references is obtained as follows.

  • For an item in $uri-sequence that is an instance of xs:string, xs:anyURI, or xs:untypedAtomic, the value is cast to xs:anyURI. If the resulting URI reference is an absolute URI reference then it is used as is. If it is a relative URI reference, then it is resolved against the base URI of $base-node if supplied, or against the base URI from the static context otherwise (this will usually be the base URI of the stylesheet module). A relative URI reference is resolved against a base URI using the rules defined in [RFC3986].

  • For an item in $uri-sequence that is a node, the node is atomized. The result must be a sequence whose items are all instances of xs:string, xs:anyURI, or xs:untypedAtomic. Each of these values is cast to xs:anyURI, and if the resulting URI reference is an absolute URI reference then it is used as is. If it is a relative URI reference, then it is resolved against the base URI of $base-node if supplied, or against the base URI of the node that contained it otherwise.

Each of these absolute URI references is then processed as follows. Any fragment identifier that is present in the URI reference is removed, and the resulting absolute URI is cast to a string and then passed to the docFO30 function defined in [Functions and Operators]. This returns a document node. If an error occurs during evaluation of the docFO30 function, the processor may either signal this error in the normal way, or may recover by ignoring the failure, in which case the failing URI will not contribute any nodes to the result of the document function.

If the URI reference contained no fragment identifier, then this document node is included in the sequence of nodes returned by the document function.

If the URI reference contained a fragment identifier, then the fragment identifier is interpreted according to the rules for the media type of the resource representation identified by the URI, and is used to select zero or more nodes that are descendant-or-self nodes of the returned document node. As described in 2.3 Initiating a Transformation, the media type is available as part of the evaluation context for a transformation.

The sequence of nodes returned by the function is in document order, with no duplicates. This order has no necessary relationship to the order in which URIs were supplied in the $uri-sequence argument.

Error Conditions

[ERR XTDE1160] When a URI reference contains a fragment identifier, it is a dynamic error if the media type is not one that is recognized by the processor, or if the fragment identifier does not conform to the rules for fragment identifiers for that media type, or if the fragment identifier selects something other than a sequence of nodes (for example, if it selects a range of characters within a text node).

A processor may provide an option which, if selected, causes the processor instead of signaling this error, to ignore the fragment identifier and return the document node.

The set of media types recognized by a processor is implementation-defined.

[ERR XTDE1162] When a URI reference is a relative reference, it is a dynamic error if no base URI is available to resolve the relative reference. This can arise for example when the URI is contained in a node that has no base URI (for example a parentless text node), or when the second argument to the function is a node that has no base URI, or when the base URI from the static context is undefined.

Notes

One effect of these rules is that unless XML entities or xml:base are used, and provided that the base URI of the stylesheet module is known, document("") refers to the document node of the containing stylesheet module (the definitive rules are in [RFC3986]). The XML resource containing the stylesheet module is processed exactly as if it were any other XML document, for example there is no special recognition of xsl:text elements, and no special treatment of comments and processing instructions.

The XPath rules for function calling ensure that it is a type error if the supplied value of the second argument is anything other than a single node. If XPath 1.0 compatibility mode is enabled, then a sequence of nodes may be supplied, and the first node in the sequence will be used.

20.2 Keys

Keys provide a way to work with documents that contain an implicit cross-reference structure. They make it easier to locate the nodes within a document that have a given value for a given attribute or child element, and they provide a hint to the implementation that certain access paths in the document need to be efficient.

20.2.1 The xsl:key Declaration

<!-- Category: declaration -->
<xsl:key
  name = eqname
  match = pattern
  use? = expression
  composite? = "yes" | "no"
  collation? = uri >
  <!-- Content: sequence-constructor -->
</xsl:key>

The xsl:key declaration is used to declare keys. The name attribute specifies the name of the key. The value of the name attribute is an EQName, which is expanded as described in 5.1 Qualified Names. The match attribute is a Pattern; an xsl:key element applies to all nodes that match the pattern specified in the match attribute.

[Definition: A key is defined as a set of xsl:key declarations in the same package that share the same name.]

The key name is scoped to the containing package, and is available for use in calls to the key function within that package.

The value of the key may be specified either using the use attribute or by means of the contained sequence constructor.

[ERR XTSE1205] It is a static error if an xsl:key declaration has a use attribute and has non-empty content, or if it has empty content and no use attribute.

If the use attribute is present, its value is an expression specifying the values of the key. The expression will be evaluated with a singleton focus based on the node that matches the pattern. The result of evaluating the expression is atomized.

Similarly, if a sequence constructor is present, it is used to determine the values of the key. The sequence constructor will be evaluated with the node that matches the pattern as the context node. The result of evaluating the sequence constructor is atomized.

[Definition: The expression in the use attribute and the sequence constructor within an xsl:key declaration are referred to collectively as the key specifier. The key specifier determines the values that may be used to find a node using this key.]

When evaluation of the key specifier results in a sequence (after atomization) containing more than one atomic value, the effect depends on the value of the composite attribute:

  • When the attribute is absent or has the value no, each atomic value in the sequence acts as an individual key. For example, if match="book" use="author" composite="no" is specified, then a book element may be located using the value of any author element.

  • When the attribute is present and has the value yes, the sequence of atomic values is treated as a composite key that must be matched in its entirety. For example, if match="book" use="author" composite="yes" is specified, then a book element may be located using the value of all its author elements, supplied in the correct order.

If there are several xsl:key declarations in the same package with the same key name, then they must all have the same effective value for their composite attribute. The effective value is the actual value of the attribute if present, or "no" if the attribute is absent.

Note:

There is no requirement that all the values of a key should have the same type.

The presence of an xsl:key declaration makes it easy to find a node that matches the match pattern if the values of the key specifier (when applied to that node) are known. It also provides a hint to the implementation that access to the nodes by means of these values needs to be efficient (many implementations are likely to construct an index or hash table to achieve this).

Note:

An xsl:key declaration is not bound to a specific source document. The source document to which it applies is determined only when the key function is used to locate nodes using the key. Keys can be used to locate nodes within any source document (including temporary trees), but each use of the key function searches one document only.

The optional collation attribute is used only when deciding whether two strings are equal for the purposes of key matching. Specifically, two key values $a and $b are considered equal if the result of the function call deep-equal($a, $b, $collation) is true. The effective collation for an xsl:key declaration is the collation specified in its collation attribute if present, resolved against the base URI of the xsl:key element, or the default collation that is in scope for the xsl:key declaration otherwise; the effective collation must be the same for all the xsl:key declarations making up a key.

[ERR XTSE1210] It is a static error if the xsl:key declaration has a collation attribute whose value (after resolving against the base URI) is not a URI recognized by the implementation as referring to a collation.

[ERR XTSE1220] It is a static error if there are several xsl:key declarations in the same package with the same key name and different effective collations. Two collations are the same if their URIs are equal under the rules for comparing xs:anyURI values, or if the implementation can determine that they are different URIs referring to the same collation.

[ERR XTSE1222] It is a static error if there are several xsl:key declarations in the stylesheet with the same key name and different effective values for the composite attribute.

It is possible to have:

  • multiple xsl:key declarations with the same name;

  • a node that matches the match patterns of several different xsl:key declarations, whether these have the same key name or different key names;

  • a node that returns more than one value from its key specifier (which can be treated either as separate individual key values, or as a single composite key value);

  • a key value that identifies more than one node (the key values for different nodes do not need to be unique).

An xsl:key declaration with higher import precedence does not override another of lower import precedence; all the xsl:key declarations in the stylesheet are effective regardless of their import precedence.

20.2.2 fn:key

Summary

Returns the nodes that match a supplied key value.

Signatures

key( $key-name  as xs:string,
$key-value  as xs:anyAtomicType*) as node()*
key( $key-name  as xs:string,
$key-value  as xs:anyAtomicType*,
$top  as node()) as node()*
Properties

The two-argument form of this function is deterministicFO30, focus-dependentFO30, and context-dependentFO30.

The three-argument form of this function is deterministicFO30, focus-independentFO30, and context-dependentFO30.

Rules

The key function does for keys what the element-with-idFO30 function does for IDs.

The $key-name argument specifies the name of the key. The value of the argument must be a string containing an EQName. If it is a lexical QName, then it is expanded as described in 5.1 Qualified Names (no prefix means no namespace).

The $key-value argument to the key function is considered as a sequence. The effect depends on the value of the composite attribute of the corresponding xsl:key declaration.

  • If composite is no or absent, the set of requested key values is formed by atomizing the supplied value of the argument, using the standard function conversion rules. Each of the resulting atomic values is considered as a requested key value. The result of the function is a sequence of nodes, in document order and with duplicates removed, comprising those nodes in the selected subtree (see below) that are matched by an xsl:key declaration whose name is the same as the supplied key name, where the result of evaluating the key specifier contains a value that is equal to one of these requested key values, under the rules appropriate to the XPath eq operator for the two values in question, using the collation attributes of the xsl:key declaration when comparing strings. No error is reported if two values are encountered that are not comparable; they are regarded for the purposes of this function as being not equal.

    If the second argument is an empty sequence, the result of the function will be an empty sequence.

  • If composite is yes, the requested key value is the sequence formed by atomizing the supplied value of the argument, using the standard function conversion rules. The result of the function is a sequence of nodes, in document order and with duplicates removed, comprising those nodes in the selected subtree (see below) that are matched by an xsl:key declaration whose name is the same as the supplied key name, where the result of evaluating the key specifier is deep-equal to the requested key value, under the rules appropriate to the deep-equalFO30 function applied to the two values in question, using the collation attributes of the xsl:key declaration when comparing strings. Note that the deep-equalFO30 function reports no error if two values are encountered that are not comparable; they are regarded for the purposes of this function as being not equal.

    If the second argument is an empty sequence, the result of the function will be the set of nodes having an empty sequence as the value of the key specifier.

Different rules apply when XSLT 1.0 compatible behavior is enabled.

A key (that is, a set of xsl:key declarations sharing the same key name) is processed in backwards compatible mode if (a) at least one of the xsl:key elements in the definition of the key enables backwards compatible behavior, and (b) the effective value of the composite attribute is no.

When a key is processed in backwards compatible mode, then:

The result of evaluating the key specifier in any xsl:key declaration having this key name is converted after atomization to a sequence of strings, by applying a cast to each item in the sequence.

When the first argument to the key function specifies this key name, then the value of the second argument is converted after atomization to a sequence of strings, by applying a cast to each item in the sequence. The values are then compared as strings.

The third argument is used to identify the selected subtree. If the argument is present, the selected subtree is the set of nodes that have $top as an ancestor-or-self node. If the argument is omitted, the selected subtree is the document containing the context node. This means that the third argument effectively defaults to /.

The result of the key function can be described more specifically as follows. The result is a sequence containing every node $N that satisfies the following conditions:

  • $N/ancestor-or-self::node() intersect $top is non-empty. (If the third argument is omitted, $top defaults to /)

  • $N matches the pattern specified in the match attribute of an xsl:key declaration whose name attribute matches the name specified in the $key-name argument.

  • When composite="no", and the key specifier of that xsl:key declaration is evaluated with a singleton focus based on $N, the atomized value of the resulting sequence includes a value that compares equal to at least one item in the atomized value of the sequence supplied as $key-value, under the rules of the eq operator with the collation selected as described above.

    When composite="yes", and the key specifier of that xsl:key declaration is evaluated with a singleton focus based on $N, the atomized value of the resulting sequence compares equal to the atomized value of the sequence supplied as $key-value, under the rules of the deep-equalFO30 function with the collation selected as described above.

The sequence returned by the key function will be in document order, with duplicates (that is, nodes having the same identity) removed.

Error Conditions

[ERR XTDE1260] It is a dynamic error if the value is not a valid QName, or if there is no namespace declaration in scope for the prefix of the QName, or if the name obtained by expanding the QName is not the same as the expanded name of any xsl:key declaration in the containing package. If the processor is able to detect the error statically (for example, when the argument is supplied as a string literal), then the processor may optionally signal this as a static error.

[ERR XTDE1270] It is a dynamic error to call the key function with two arguments if there is no context node, or if the root of the tree containing the context node is not a document node; or to call the function with three arguments if the root of the tree containing the node supplied in the third argument is not a document node.

Notes

Untyped atomic values are converted to strings, not to the type of the other operand. This means, for example, that if the expression in the use attribute returns a date, supplying an untyped atomic value in the call to the key function will return an empty sequence.

Examples
Example: Using a Key to Follow Cross-References

Given a declaration

<xsl:key name="idkey" match="div" use="@id"/>

an expression key("idkey",@ref) will return the same nodes as id(@ref), assuming that the only ID attribute declared in the XML source document is:

<!ATTLIST div id ID #IMPLIED>

and that the ref attribute of the context node contains no whitespace.

 

Example: Using a Key to Generate Hyperlinks

Suppose a document describing a function library uses a prototype element to define functions

<prototype name="sqrt" return-type="xs:double">
  <arg type="xs:double"/>
</prototype>

and a function element to refer to function names

<function>sqrt</function>

Then the stylesheet could generate hyperlinks between the references and definitions as follows:

<xsl:key name="func" match="prototype" use="@name"/>

<xsl:template match="function">
<b>
  <a href="#{generate-id(key('func',.))}">
    <xsl:apply-templates/>
  </a>
</b>
</xsl:template>

<xsl:template match="prototype">
  <p>
    <a name="{generate-id()}">
      <b>Function: </b>
      ...
    </a>
  </p>
  </xsl:template>

When called with two arguments, the key function always returns nodes that are in the same document as the context node. To retrieve a node from any other document, it is necessary either to change the context node, or to supply a third argument.

Example: Using Keys to Reference other Documents

For example, suppose a document contains bibliographic references in the form <bibref>XSLT</bibref>, and there is a separate XML document bib.xml containing a bibliographic database with entries in the form:

<entry name="XSLT">...</entry>

Then the stylesheet could use the following to transform the bibref elements:

<xsl:key name="bib" match="entry" use="@name"/>

<xsl:template match="bibref">
  <xsl:variable name="name" select="."/>
  <xsl:apply-templates select="document('bib.xml')/key('bib',$name)"/>
</xsl:template>

Note:

This relies on the ability in XPath 2.0 to have a function call on the right-hand side of the / operator in a path expression.

The following code would also work:

<xsl:key name="bib" match="entry" use="@name"/>

<xsl:template match="bibref">
  <xsl:apply-templates select="key('bib', ., document('bib.xml'))"/>
</xsl:template>

 

Example: Using a Composite Key

This example uses a composite key consisting of first name and last name to locate employees in an employee file.

The key can be defined like this:

<xsl:key name="emp-name-key" 
         match="employee" 
         use="name/first, name/last" 
         composite="yes"/>                     
         

A particular employee can then be located using the function call:

key('emp-name-key', ('Tim', 'Berners-Lee'), doc('employees.xml'))

20.3 Miscellaneous Additional Functions

20.3.1 fn:current

Summary

Returns the item that is the context item for the evaluation of the containing XPath expression

Signature

current() as item()
Properties

This function is deterministicFO30, context-dependentFO30, and focus-dependentFO30.

Rules

The current function, used within an XPath expression, returns the item that was the context item at the point where the expression was invoked from the XSLT stylesheet. This is referred to as the current item. For an outermost expression (an expression not occurring within another expression), the current item is always the same as the context item. Thus,

<xsl:value-of select="current()"/>

means the same as

<xsl:value-of select="."/>

However, within square brackets, or on the right-hand side of the / operator, the current item is generally different from the context item.

If the current function is used within a pattern, its value is the item that is being matched against the pattern.

Error Conditions

[ERR XTDE1360] If the current function is evaluated within an expression that is evaluated when the context item is absent, a dynamic error occurs.

When the current is called by means of a dynamic function call (for example, current#0()), it is evaluated as if the context item is absent ([see ERR XTDE1360]).

Examples

The instruction:

<xsl:apply-templates select="//glossary/entry[@name=current()/@ref]"/>

will process all entry elements that have a glossary parent element and that have a name attribute with value equal to the value of the current item's ref attribute. This is different from

<xsl:apply-templates select="//glossary/entry[@name=./@ref]"/>

which means the same as

<xsl:apply-templates select="//glossary/entry[@name=@ref]"/>

and so would process all entry elements that have a glossary parent element and that have a name attribute and a ref attribute with the same value.

20.3.2 fn:unparsed-entity-uri

Summary

Returns the URI (system identifier) of an unparsed entity

Signature

unparsed-entity-uri($entity-name as xs:string) as xs:anyURI
Properties

This function is deterministicFO30, focus-dependentFO30, and context-dependentFO30.

Rules

The unparsed-entity-uri function returns the URI of the unparsed entity whose name is given by the value of the $entity-name argument, in the document containing the context node. It returns the zero-length xs:anyURI if there is no such entity. This function maps to the dm:unparsed-entity-system-id accessor defined in [Data Model].

Error Conditions

[ERR XTDE1370] It is a dynamic error if the unparsed-entity-uri function is called when there is no context node, or when the root of the tree containing the context node is not a document node.

20.3.3 fn:unparsed-entity-public-id

Summary

Returns the public identifier of an unparsed entity

Signature

unparsed-entity-public-id($entity-name as xs:string) as xs:anyURI
Properties

This function is deterministicFO30, focus-dependentFO30, and context-dependentFO30.

Rules

The unparsed-entity-public-id function returns the public identifier of the unparsed entity whose name is given by the value of the $entity-name argument, in the document containing the context node. It returns the zero-length string if there is no such entity, or if the entity has no public identifier. This function maps to the dm:unparsed-entity-public-id accessor defined in [Data Model].

Error Conditions

[ERR XTDE1380] It is a dynamic error if the unparsed-entity-public-id function is called when there is no context node, or when the root of the tree containing the context node is not a document node.

20.3.4 fn:system-property

Summary

Returns the value of a system property

Signature

system-property($property-name as xs:string) as xs:string
Properties

This function is deterministicFO30, focus-independentFO30, and context-dependentFO30.

Rules

The $property-name argument must evaluate to a lexical QName. The lexical QName is expanded as described in 5.1 Qualified Names.

The system-property function returns a string representing the value of the system property identified by the name. If there is no such system property, the zero-length string is returned.

Implementations must provide the following system properties, which are all in the XSLT namespace:

  • xsl:version, a number giving the version of XSLT implemented by the processor; for implementations conforming to the version of XSLT specified by this document, this is the string "3.0". The value will always be a string in the lexical space of the decimal data type defined in XML Schema (see [XML Schema Part 2]). This allows the value to be converted to a number for the purpose of magnitude comparisons.

  • xsl:vendor, a string identifying the implementer of the processor

  • xsl:vendor-url, a string containing a URL identifying the implementer of the processor; typically this is the host page (home page) of the implementer's Web site.

  • xsl:product-name, a string containing the name of the implementation, as defined by the implementer. This should normally remain constant from one release of the product to the next. It should also be constant across platforms in cases where the same source code is used to produce compatible products for multiple execution platforms.

  • xsl:product-version, a string identifying the version of the implementation, as defined by the implementer. This should normally vary from one release of the product to the next, and at the discretion of the implementer it may also vary across different execution platforms.

  • xsl:is-schema-aware, returns the string "yes" in the case of a processor that claims conformance as a schema-aware XSLT processor, or "no" in the case of a basic XSLT processor.

  • xsl:supports-serialization, returns the string "yes" in the case of a processor that offers the serialization feature, or "no" otherwise.

  • xsl:supports-backwards-compatibility, returns the string "yes" in the case of a processor that offers the XSLT 1.0 compatibility feature, or "no" otherwise.

  • xsl:supports-namespace-axis, returns the string "yes" in the case of a processor that offers the XPath namespace axis even when not in backwards compatible mode, or "no" otherwise. Note that a processor that supports backwards compatible mode must support the namespace axis when in that mode, so this property is not relevant to that case.

  • xsl:supports-streaming, returns the string "yes" in the case of a processor that offers the streaming feature (see 26.5 Streaming Feature), or "no" otherwise.

  • xsl:supports-dynamic-evaluation, returns the string "yes" in the case of a processor that offers the dynamic evaluation feature (see 26.6 Dynamic Evaluation Feature), or "no" otherwise.

Some of these properties relate to the conformance levels and features offered by the processor: these options are described in 26 Conformance.

The actual values returned for the above properties are implementation-defined.

The set of system properties that are supported, in addition to those listed above, is also implementation-defined. Implementations must not define additional system properties in the XSLT namespace.

Error Conditions

[ERR XTDE1390] It is a dynamic error if the value supplied as the $property-name argument is not a valid QName, or if there is no namespace declaration in scope for the prefix of the QName. If the processor is able to detect the error statically (for example, when the argument is supplied as a string literal), then the processor may optionally signal this as a static error.

Notes

An implementation must not return the value 3.0 as the value of the xsl:version system property unless it is conformant to XSLT 3.0.

It is recognized that vendors who are enhancing XSLT 1.0 or 2.0 processors may wish to release interim implementations before all the mandatory features of this specification are implemented. Since such products are not conformant to XSLT 3.0, this specification cannot define their behavior. However, implementers of such products are encouraged to return a value for the xsl:version system property that is intermediate between 1.0 and 3.0, and to provide the element-available and function-available functions to allow users to test which features have been fully implemented.

21 XPath Extensions

XSLT 3.0 extends the type system and data model of XPath 3.0 with additional datatypes and associated functions and operators defined in this section.

21.1 Maps

A map is an additional kind of item.

[Definition: A map consists of a set of entries. Each entry comprises a key which is an arbitrary atomic value, and an arbitrary sequence called the associated value.]

[Definition: Within a map, no two entries have the same key. Two atomic values K1 and K2 are the same key for this purpose if the relation deep-equal(K1, K2, $UCC) holds, where $UCC is the Unicode codepoint collation.]

To put it another way, the keys are the same if either K1 eq K2 is true under the Unicode codepoint collation, or if both K1 and K2 are NaN. It is not necessary that all the keys should be mutually comparable (for example, they can include a mixture of integers and strings).

The function call map:get($map, $key) can be used to retrieve the value associated with a given key.

A map can also be viewed as a function from keys to associated values. To achieve this, a map is also a function item. The properties of this function are as follows:

  • The name of the function is absent.

  • The arity of the function is 1 (one).

  • The parameter names comprise a sequence of one QName, conventionally $key, though the choice of name has no observable consequences.

  • The signature is function($key as xs:anyAtomicValue) as item()* (with no annotations).

  • The implementation is the expression map:get($self, $key)

  • The non-local-variable-bindings comprise a single variable, $self, whose value is the map itself.

Calling the function has the same effect as calling the get function: the expression $map($key) returns the same result as get($map, $key). For example, if $books-by-isbn is a map whose keys are ISBNs and whose associated values are book elements, then the expression $books-by-isbn("0470192747") returns the book element with the given ISBN. The fact that a map is a function item allows it to be passed as an argument to higher-order functions that expect a function item as one of their arguments.

Like all other values, maps are immutable. For example, the map:remove function creates a new map by removing an entry from an existing map, but the existing map is not changed by the operation.

Like sequences, maps have no identity. It is meaningful to compare the contents of two maps, but there is no way of asking whether they are "the same map": two maps with the same content are indistinguishable.

21.1.1 The Type of a Map

The syntax of ItemTypeXP30 as defined in XPath is extended as follows:

MapType
[69]    ItemType    ::=    KindTest | ("item" "(" ")") | FunctionTest | AtomicOrUnionType | ParenthesizedItemType
| MapType
[201]    MapType    ::=    'map' '(' ( '*' | (AtomicOrUnionTypeXP30 ',' SequenceTypeXP30) ')'

The following rules express the matching rules for a map item type and a map, and extend the set of rules given in Section 2.5.5.2 Matching an ItemType and an Item XP30:

  • The ItemType map(K, V) matches an item M if (a) M is a map, and (b) every entry in M has a key that matches K and an associated value that matches V. For example, map(xs:integer, element(employee)) matches a map if all the keys in the map are integers, and all the associated values are employee elements. Note that a map (like a sequence) carries no intrinsic type information separate from the types of its entries, and the type of existing entries in a map does not constrain the type of new entries that can be added to the map.

    Note:

    In consequence, map(K, V) matches an empty map, whatever the types K and V might be.

  • The ItemType map(*) matches any map regardless of its contents. It is equivalent to map(xs:anyAtomicType, item()*).

A map also acts as a function. This means that maps match certain function item types. Specifically, the following rule extends the list of rules in Section 2.5.5.7 Function Test XP30:

  • function(*) matches any map.

  • function(xs:anyAtomicType) as item()* matches any map.

Because of the rules for subtyping of function types according to their signature, it follows that the item type function(A) as item()*, where A is an atomic type, also matches any map, regardless of the type of the keys actually found in the map. For example, a map whose keys are all strings can be supplied where the required type is function(xs:integer) as item()*; a call on the map that treats it as a function with an integer argument will always succeed, and will always return an empty sequence.

The function signature of the map, treated as a function, is always function(xs:anyAtomicType) as item()*, regardless of the actual types of the keys and values in the map. This means that a function item type with a more specific return type, such as function(xs:anyAtomicType) as xs:integer, does not match a map in the sense required to satisfy the instance of operator. However, the rules for function coercion mean that any map can be supplied as a value in a context where such a type is the required type, and a type error will only occur if an actual call on the map (treated as a function) returns a value that is not an instance of the required return type.

Note:

So, given a map $M whose keys are integers and whose results are strings, such as map{0:"no", 1:"yes"}, the following relations hold, among others:

  • $M instance of map(*)

  • $M instance of map(xs:integer, xs:string)

  • $M instance of map(xs:decimal, xs:anyAtomicType)

  • not($M instance of map(xs:int, xs:string))

  • not($M instance of map(xs:integer, xs:token))

  • $M instance of function(*)

  • $M instance of function(xs:anyAtomicType) as item()*

  • $M instance of function(xs:integer) as item()*

  • $M instance of function(xs:int) as item()*

  • $M instance of function(xs:string) as item()*

  • not($M instance of function(xs:integer) as xs:string)

The last case might seem surprising; however, function coercion ensures that $M can be used successfully anywhere that the required type is function(xs:integer) as xs:string.

The rules for judging whether one item type is a subtype of another, given in Section 2.5.6.2 The judgement subtype-itemtype(Ai, Bi) XP30, are extended with some additional rules. The judgement subtype-itemtype(Ai, Bi) is true if:

  • Ai is map(*) and Bi is map(K, V), for any K and V.

  • Ai is map(Ka, Va) and Bi is map(Kb, Vb), where subtype-itemtype(Kb, Ka) and subtype-itemtype(Vb, Va).

  • Ai is function(*) and Bi is map(*), (or, because of the transitivity rules, any other map type).

  • Ai is function(xs:anyAtomicType) as item()* and Bi is map(*), (or, because of the transitivity rules, any other map type).

21.1.2 Functions that Operate on Maps

The functions defined in this section use a conventional namespace prefix map, which is assumed to be bound to the namespace URI http://www.w3.org/2005/xpath-functions/map.

There is no operation to atomize a map or convert it to a string.

The number of entries in the map may be obtained as count(map:keys($map)).

21.1.2.1 map:new
Summary

Creates a new map: either an empty map, or a map that combines entries from a number of existing maps.

Signatures

new() as map(*)
new($maps as map(*)*) as map(*)
Properties

This function is deterministicFO30, context-independentFO30, and focus-independentFO30.

Rules

The function map:new constructs and returns a new map.

The zero-argument form of the function returns an empty map. It is equivalent to calling the one-argument form of the function with an empty sequence as the value of the first argument.

The one-argument form of the function returns a map that is formed by combining the contents of the maps supplied in the $input argument.

The supplied maps are combined as follows:

  1. There is one entry in the new map for each distinct key value present in the union of the input maps, where two keys are distinct if they are not the same key.

  2. The associated value for each such key is taken from the last map in the input sequence $input that contains an entry with this key.

There is no requirement that the supplied input maps should have the same or compatible types. The type of a map (for example map(xs:integer, xs:string)) is descriptive of the entries it currently contains, but is not a constraint on how the map may be combined with other maps.

Examples

let $week := map{0:"Sonntag", 1:"Montag", 2:"Dienstag", 3:"Mittwoch", 4:"Donnerstag", 5:"Freitag", 6:"Samstag"}

The expression map:new() returns map{}. (Returns an empty map).

The expression map:new(()) returns map{}. (Returns an empty map).

The expression map:new((map:entry(0, "no"), map:entry(1, "yes"))) returns map{0:"no", 1:"yes"}. (Returns a map with two entries).

The expression map:new(($week, {7:"Unbekannt"})) returns map{0:"Sonntag", 1:"Montag", 2:"Dienstag", 3:"Mittwoch", 4:"Donnerstag", 5:"Freitag", 6:"Samstag", 7:"Unbekannt"}. (The value of the existing map is unchanged; a new map is created containing all the entries from $week, supplemented with a new entry.).

The expression map:new(($week, {6:"Sonnabend"})) returns map{0:"Sonntag", 1:"Montag", 2:"Dienstag", 3:"Mittwoch", 4:"Donnerstag", 5:"Freitag", 6:"Sonnabend"}. (The value of the existing map is unchanged; a new map is created containing all the entries from $week, with one entry replaced by a new entry. Both input maps contain an entry with the key value 6; the one used in the result is the one that comes last in the input sequence.).

21.1.2.2 map:keys
Summary

Returns a sequence containing all the key values present in a map

Signature

keys($input as map(*)) as xs:anyAtomicType*
Properties

This function is deterministicFO30, context-independentFO30, and focus-independentFO30.

Rules

The function map:keys takes any map as its $input argument and returns the keys that are present in the map as a sequence of atomic values, in implementation-dependent order.

Notes

The number of items in the result will be the same as the number of entries in the map, and the result sequence will contain no duplicate values.

Examples

The expression map:keys(map{1:"yes", 2:"no"}) returns some permutation of (1,2). (The result is in implementation-dependent order.).

21.1.2.3 map:contains
Summary

Tests whether a supplied map contains an entry for a given key

Signature

contains( $map  as map(*),
$key  as xs:anyAtomicType) as xs:boolean
Properties

This function is deterministicFO30, context-independentFO30, and focus-independentFO30.

Rules

The function map:contains returns true if the map supplied as $map contains an entry with the same key as the supplied value of $key; otherwise it returns false. The equality comparison uses the Unicode codepoint collation; no error occurs if the map contains keys that are not comparable with the supplied $key.

If the supplied key is xs:untypedAtomic, it is compared as an instance of xs:string. If the supplied key is the xs:float or xs:double value NaN, the function returns true if there is an entry whose key is NaN, or false otherwise.

Examples

let $week := map{0:"Sonntag", 1:"Montag", 2:"Dienstag", 3:"Mittwoch", 4:"Donnerstag", 5:"Freitag", 6:"Samstag"}

The expression map:contains($week, 2) returns true().

The expression map:contains($week, 9) returns false().

The expression map:contains(map{}, "xyz") returns false().

The expression map:contains(map{"xyz":23}, "xyz") returns true().

The expression map:contains(map{"abc":23, "xyz":()}, "xyz") returns true().

21.1.2.4 map:get
Summary

Returns the value associated with a supplied key in a given map.

Signature

get( $map  as map(*),
$key  as xs:anyAtomicType) as item()*
Properties

This function is deterministicFO30, context-independentFO30, and focus-independentFO30.

Rules

The function map:get attempts to find an entry within the map supplied as $map that has the same key as the supplied value of $key. If there is such an entry, it returns the associated value; otherwise it returns an empty sequence. The comparison uses the Unicode codepoint collation; no error occurs if the map contains keys that are not comparable with the supplied $key.

If the supplied key is xs:untypedAtomic, it is compared as an instance of xs:string. If the supplied key is the xs:float or xs:double value NaN, the function returns the value in the entry whose key is NaN, if there is such an entry, or the empty sequence otherwise.

Where values of different numeric types are numerically very close to each other, it can happen that the map contains two entries whose keys both match the supplied key, but which are not equal to each other. In this situation the entry that is returned is implementation-dependent.

Notes

A return value of () from map:get could indicate that the key is present in the map with an associated value of (), or it could indicate that the key is not present in the map. The two cases can be distinguished by calling map:contains.

Invoking the map as a function item has the same effect as calling get: that is, when $map is a map, the expression $map($K) is equivalent to map:get($map, $K). Similarly, the expression map:get(map:get(map:get($map, 'employee'), 'name'), 'first') can be written as $map('employee')('name')('first').

Examples

let $week := map{0:"Sonntag", 1:"Montag", 2:"Dienstag", 3:"Mittwoch", 4:"Donnerstag", 5:"Freitag", 6:"Samstag"}

The expression map:get($week, 4) returns "Donnerstag".

The expression map:get($week, 9) returns (). (When the key is not present, the function returns an empty sequence.).

The expression map:get(map:entry(7,()), 7) returns (). (An empty sequence as the result can also signify that the key is present and the associated value is an empty sequence.).

21.1.2.5 map:entry
Summary

Creates a map that contains a single entry (a key-value pair).

Signature

entry( $key  as xs:anyAtomicType,
$value  as item()*) as map(*)
Properties

This function is deterministicFO30, context-independentFO30, and focus-independentFO30.

Rules

The function map:entry returns a new map which contains a single entry. The key of the entry in the new map is $key, and its associated value is $value.

Notes

The function map:entry is intended primarily for use in conjunction with the function map:new. For example, a map containing seven entries may be constructed like this:

map:new((
   map:entry("Su", "Sunday"),
   map:entry("Mo", "Monday"),
   map:entry("Tu", "Tuesday"),
   map:entry("We", "Wednesday"),
   map:entry("Th", "Thursday"),
   map:entry("Fr", "Friday"),
   map:entry("Sa", "Saturday")
   ))

Unlike the map expression ({...}), this technique can be used to construct a map with a variable number of entries, for example:

map:new(for $b in //book return map:entry($b/isbn, $b))
Examples

The expression map:entry("M", "Monday") returns {"M":"Monday"}.

21.1.2.6 map:remove
Summary

Constructs a new map by removing an entry from an existing map

Signature

remove( $map  as map(*),
$key  as xs:anyAtomicType) as map(*)
Properties

This function is deterministicFO30, context-independentFO30, and focus-independentFO30.

Rules

The function map:remove returns a new map. The entries in the new map correspond to the entries of $map, excluding any entry whose key is the same key as $key.

No failure occurs if the input map contains no entry with the supplied key; the input map is returned unchanged

Examples

let $week := map{0:"Sonntag", 1:"Montag", 2:"Dienstag", 3:"Mittwoch", 4:"Donnerstag", 5:"Freitag", 6:"Samstag"}

The expression map:remove($week, 4) returns map{0:"Sonntag", 1:"Montag", 2:"Dienstag", 3:"Mittwoch", 5:"Freitag", 6:"Samstag"}.

The expression map:remove($week, 23) returns map{0:"Sonntag", 1:"Montag", 2:"Dienstag", 3:"Mittwoch", 4:"Donnerstag", 5:"Freitag", 6:"Samstag"}.

21.1.2.7 map:for-each-entry
Summary

Applies a supplied function to every entry in a map, returning the concatenation of the results.

Signature

for-each-entry( $input  as map(*),
$action  as function($key as xs:anyAtomicType, $value as item()*)) as item()*
Properties

This function is deterministicFO30, context-independentFO30, and focus-independentFO30.

Rules

The function map:for-each-entry takes any map as its $input argument and applies the supplied function to each entry in the map, in implementation-dependent order; the result is the sequence obtained by concatenating the results of these function calls.

The function supplied as $action takes two arguments. It is called supplying the key of the map entry as the first argument, and the associated value as the second argument.

Examples

The expression map:for-each-entry(map{1:"yes", 2:"no"}, function($k, $v){$k}) returns some permutation of (1,2). (This function call is equivalent to calling map:keys. The result is in implementation-dependent order.).

The expression distinct-values(map:for-each-entry(map{1:"yes", 2:"no"}, function($k, $v){$v}) returns some permutation of ("yes", "no"). (This function call returns the distinct values present in the map, in implementation-dependent order.).

The expression map:new(map:for-each-entry(map{"a":1, "b":2}, function($k, $v){map:entry($k, $v+1)}) returns map{"a":2, "b":3}. (This function call returns a map with the same keys as the input map, with the value of each entry increased by one.).

Example: Converting a Map to an Element Node

This example converts the entries in a map to attributes on a newly constructed element node.

   <xsl:variable name="dimensions" 
                 select="map{'height': 3, 'width': 4, 'depth': 5}"/>
   
   <xsl:function name="f:make-attribute" as="attribute()">
     <xsl:param name="key" as="xs:string"/>
     <xsl:param name="value" as="xs:anyAtomicType"/>
     <xsl:attribute name="{$key}" select="string($value)"/>
   </xsl:function>
   
   <xsl:template name="convert">
     <box>
       <xsl:sequence select="map:for-each-entry(
                               $dimensions, f:make-attribute#2)"/>
     </box>
   </xsl:template>  
   

The result is the element <box height="3" width="4" depth="5"/>.

21.1.2.8 fn:collation-key
Summary

Given a key value and a collation, generates an internal value with the property that the internal value is the same for any two keys that compare equal under the given collation.

Signatures

collation-key($key as xs:string) as xs:anyAtomicType
collation-key( $key  as xs:string,
$collation  as xs:string) as xs:anyAtomicType
Properties

This function is deterministicFO30, context-dependentFO30, and focus-independentFO30. It depends on collations.

Rules

Calling the one-argument version of this function is equivalent to calling the two-argument version supplying the default collation as the second argument.

The function returns an implementation-defined value with the property that collation-key($K1, $C) eq collation-key($K2, $C) if and only if compare($K1, $K2, $C) = 0.

If the collation URI is a relative reference, it is resolved against the static base URI.

An implementation is free to generate a collation key in any convenient way provided that it always generates the same collation key for two strings that are equal under the collation, and different collation keys for strings that are not equal. This holds only within a single execution scopeFO30; an implementation is under no obligation to generate the same collation keys during a subsequent unrelated query or transformation.

It is possible to define collations that do not have the ability to generate collation keys. Supplying such a collation will cause the function to fail. The ability to generate collation keys is an implementation-defined property of the collation.

Error Conditions

An error is raised [ERR FOCH0004] FO30 if the specified collation does not support the generation of collation keys.

Notes

The function is provided primarily for use with maps. If a map is required where codepoint equality is inappropriate for comparing keys, then a common technique is to normalize the key value so that equality matching becomes feasible. There are many ways keys can be normalized, for example by use of functions such as upper-caseFO30, lower-caseFO30, normalize-spaceFO30, or normalize-unicode, but this function provides a way of normalizing them according to the rules of a specified collation. For example, if the collation ignores accents, then the function will generate the same collation key for two input strings that differ only in their use of accents.

The result of the function can be of any atomic type.

For collations based on the Unicode Collation Algorithm, an algorithm for computing collation keys is provided in [UNICODE TR10]. This algorithm generates binary collation keys, which might be materialized as a value of type xs:hexBinary or xs:base64Binary. Implementations are not required to use this algorithm.

This specification does not mandate that collation keys should retain ordering. This is partly because the primary use case is for maps, where only equality comparisons are required, and partly to allow the use of binary data types (which are currently unordered types) for the result. The specification may be revised in a future release to specify that ordering is preserved.

Examples

let $C :=

"http://www.w3.org/2005/xpath-functions/collations/UCA?strength=primary"

The expression map:new((map{collation-key("A", $C):1}, map{collation-key("a", $C):2}))(collation-key("A", $C)) returns 2. (Given that the keys of the two entries are equal under the rules of the chosen collation, only one of the entries can appear in the result; the one that is chosen is the one from the last map in the input sequence. ).

The expression let $M : map{collation-key("A", $C):1, collation-key("B", $C):2} return $M(collation-key("a", $C)) returns 1. (The strings "A" and "a" have the same collation key under this collation.).

As the above examples illustrate, it is important that when the collation-key function is used to add entries to a map, then it must also be used when retrieving entries from the map. This process can be made less error-prone by encapsulating the map within a function: function($k) {$M(collation-key($k, $collation)}.

21.1.2.10 fn:deep-equal
Summary

This function assesses whether two sequences are deep-equal to each other. The function as described here extends the definition of the XPath 3.0 deep-equalFO30 to explain how it should handle maps; it is intended to replace the existing deep-equalFO30 function at some stage in the future.

Signatures

deep-equal( $parameter1  as item()*,
$parameter2  as item()*) as xs:boolean
deep-equal( $parameter1  as item()*,
$parameter2  as item()*,
$collation  as xs:string) as xs:boolean
Properties

This function is deterministicFO30, context-dependentFO30, and focus-independentFO30. It depends on collations.

Rules

The function delivers the same result as deep-equalFO30 except when (at some level of recursion) it is necessary to compare two function items. In the case of deep-equalFO30, comparing two function items raises a dynamic error. In the case of this function, two function items that are both maps are compared as follows.

If two items $i1 and $i2 to be compared are both maps, the result is true if and only if all the following conditions apply:

  1. Both maps have the same number of entries.

  2. For every entry in the first map, there is an entry in the second map that:

    1. has the same key (note that the collation is not used when comparing keys), and

    2. has the same associated value (compared using the fn:deep-equal function, under the collation supplied in the original call to fn:deep-equal).

Error Conditions

An error is raised [ERR FOTY0015] FO30 if either input sequence contains a function item that is not a map.

Examples

The expression fn:deep-equal(map{}, map{}) returns true().

The expression fn:deep-equal(map{"a":1, "b":2}, map{"b":2, "a":1.0}) returns true().

The expression fn:deep-equal(map{"a":xs:double('NaN')}, map{"a":xs:float('NaN')}) returns true().

let $at :=

<attendees>
  <name last='Parker' first='Peter'/>
  <name last='Barker' first='Bob'/>
  <name first='Peter' last='Parker'/>
</attendees>

The expression fn:deep-equal($at, $at/*) returns false().

The expression fn:deep-equal($at/name[1], $at/name[2]) returns false().

The expression fn:deep-equal($at/name[1], $at/name[3]) returns true().

The expression fn:deep-equal($at/name[1], 'Peter Parker') returns false().

21.1.3 Map Instructions

Two instructions are added to XSLT to facilitate the construction of maps.

<!-- Category: instruction -->
<xsl:map>
  <!-- Content: sequence-constructor -->
</xsl:map>

The instruction xsl:map constructs and returns a new map.

The contained sequence constructor must evaluate to a sequence of maps: call this $maps.

The result of the instruction is then given by the XPath expression:

   
let $keys := Smaps!map:keys(.)
return if (count($keys) = count(distinct-values($keys)))
       then map:new($maps)                        
       else error()

Note:

Informally: if there are duplicate keys among the sequence of maps, a dynamic error occurs. Otherwise, the resulting map contains the union of the map entries from the supplied sequence of maps.

[ERR XTDE3365] A dynamic error occurs if the set of keys in the maps resulting from evaluating the sequence constructor contains duplicates.

There is no requirement that the supplied input maps should have the same or compatible types. The type of a map (for example map(xs:integer, xs:string)) is descriptive of the entries it currently contains, but is not a constraint on how the map may be combined with other maps.

[ERR XTTE3375] A type error occurs if the result of evaluating the sequence constructor is not an instance of the required type map(*)*.

Note:

In practice, the effect of this rule is that the sequence constructor contained in the xsl:map instruction is severely constrained: it doesn't make sense, for example, for it to contain instructions such as xsl:element that create new nodes. As with other type errors, processors are free to signal the error statically if they are able to determine that the sequence constructor would always fail when evaluated.

<!-- Category: instruction -->
<xsl:map-entry
  key = expression
  select? = expression >
  <!-- Content: sequence-constructor -->
</xsl:map-entry>

The instruction xsl:map-entry constructs and returns a singleton map: that is, a map which contains one key and one value. Such a map is primarily used as a building block when constructing maps using the xsl:map instruction.

The select attribute and the contained sequence constructor are mutually exclusive: if a select attribute is present, then the content must be empty except optionally for xsl:fallback instructions.

[ERR XTSE3280] It is a static error if the select attribute of the xsl:map-entry element is present unless the element has has no children other than xsl:fallback elements.

The key of the entry in the new map is the value obtained by evaluating the expression in the key attribute, converted to the required type xs:anyAtomicType by applying the function conversion rules. If the supplied key (after conversion) is of type xs:untypedAtomic, it is cast to xs:string.

The associated value is the value obtained by evaluating the expression in the select attribute, or the contained sequence constructor, with no conversion. If there is no select attribute and the sequence constructor is empty, the associated value is the empty sequence.

Example: Using XSLT instructions to create a fixed map

The following example binds a variable to a map whose content is statically known:

<xsl:variable name="week" as="map(xs:string, xs:string)">
  <xsl:map>
    <xsl:map-entry key="'Mo'" select="'Monday'"/>
    <xsl:map-entry key="'Tu'" select="'Tuesday'"/>
    <xsl:map-entry key="'We'" select="'Wednesday'"/>
    <xsl:map-entry key="'Th'" select="'Thursday'"/>
    <xsl:map-entry key="'Fr'" select="'Friday'"/>
    <xsl:map-entry key="'Sa'" select="'Saturday'"/>
    <xsl:map-entry key="'Su'" select="'Sunday'"/>
  </xsl:map>
</xsl:variable>  

 

Example: Using XSLT instructions to create a computed map

The following example binds a variable to a map acting as an index into a source document:

<xsl:variable name="index" as="map(xs:string, element(employee))">
  <xsl:map>
    <xsl:for-each select="//employee">
      <xsl:map-entry key="@empNr" select="."/>
    </xsl:for-each>
  </xsl:map>
</xsl:variable>  

21.1.4 Map Expressions

A new kind of expression is added to the syntax of XPath.

The syntax of PrimaryExprXP30 is extended to permit MapExpr as an additional alternative.

MapExpr
[52]    PrimaryExpr    ::=    Literal | VarRef | ParenthesizedExpr | ContextItemExpr | FunctionCall | FunctionItemExpr
| MapExpr
[202]    MapExpr    ::=    "map{" (KeyExpr ":" ValueExpr ("," KeyExpr ":" ValueExpr )*)? "}"
[203]    KeyExpr    ::=    ExprSingleXP30
[204]    ValueExpr    ::=    ExprSingleXP30

Note:

In some circumstances, it is necessary to include whitespace before or after the colon to ensure that this grammar is correctly parsed; this arises for example when the KeyExpr ends with a name and the ValueExpr starts with a name.

The value of the expression is a map whose entries correspond to the key-value pairs obtained by evaluating the successive KeyExpr and ValueExpr expressions.

Each KeyExpr expression is evaluated and atomized; a dynamic error occurs if the result is not a single atomic value. If the key value is of type xs:untypedAtomic it is converted to xs:string. The associated value is the result of evaluating the corresponding ValueExpr. If two or more entries have the same key then a dynamic error occurs [see ERR XTDE3365].

For example, the following expression constructs a map with seven entries:

map {
  "Su" : "Sunday",
  "Mo" : "Monday",
  "Tu" : "Tuesday",
  "We" : "Wednesday",
  "Th" : "Thursday",
  "Fr" : "Friday",
  "Sa" : "Saturday"
}

Note:

Unlike the map:new function, the number of entries in a map that is constructed using a map expression is known statically.

21.1.5 Maps and Streaming

Maps have many uses, but their introduction to XSLT 3.0 was strongly motivated by streaming use cases. In essence, when a source document is processed in streaming mode, data that is encountered in the course of processing may need to be retained in variables for subsequent use, because the nodes cannot be revisited. This creates a need for a flexible data structure to accommodate such temporary data, and maps were designed to fulfil this need.

The xsl:map instruction, and the XPath MapExpr construct, are exceptions to the general rule that during streaming, only one downward selection (one consuming subexpression) is permitted. They share this characteristic with xsl:fork. As with xsl:fork, a streaming processor is expected to be able to construct the map during a single pass of the streamed input document, which may require multiple expressions to be evaluated in parallel.

In the case of the xsl:map instruction, this applies only in the case where the instruction consists exclusively of xsl:map-entry (and xsl:fallback) children, and not in more complex cases where the map entries are constructed dynamically (for example using a control flow implemented using xsl:choose, xsl:for-each, or xsl:call-template).

For example, the following XPath expression is streamable, despite making two downward selections:

let $m := map{'price':xs:decimal(price), 'discount':xs:decimal(discount)} 
return ($m('price') - $m('discount'))

Analysis:

  1. Because the return clause is motionless, the sweep of the let expression is the sweep of the map expression (the expression in curly braces).

  2. The sweep of a map expression is the maximum sweep of its key/value pairs.

  3. For both key/value pairs, the key is motionless and the value is consuming.

  4. The expression carefully atomizes both values, because retaining references to streamed nodes in a variable is not permitted.

  5. Therefore the map expression, and hence the expression as a whole, is grounded and consuming.

See also: 19.8.7.15 Streamability of map expressions, 19.8.4.22 Streamability of xsl:map, 19.8.4.23 Streamability of xsl:map-entry

21.1.6 Examples using Maps

This section gives some examples of where maps can be useful.

Example: Using Maps with xsl:iterate

This example uses maps in conjunction with the xsl:iterate instruction to find the highest-earning employee in each department, in a single streaming pass of an input document containing employee records.

<xsl:stream href="employees.xml">
  <xsl:iterate select="*/employee">
    <xsl:param name="highest-earners" 
               as="map(xs:string, element(employee))" 
               select="map:new()"/>
    <xsl:variable name="this" select="copy-of(.)" as="element(employee)"/> 
    <xsl:next-iteration>
      <xsl:with-param name="highest-earners"
          select="let $existing := $highest-earners($this/department)
                  return if ($existing/salary gt $this/salary)
                         then $highest-earners
                         else map:new($highest-earners, 
                                      map:entry($this/department, $this))"/>
    </xsl:next-iteration>
    <xsl:on-completion>
      <xsl:for-each select="map:keys($highest-earners)">
        <department name="{.}">
          <xsl:copy-of select="$highest-earners(.)"/>
        </department>
      </xsl:for-each>
    </xsl:on-completion>
  </xsl:iterate>
</xsl:stream>

 

Example: Using Maps to Implement Complex Numbers

A complex number might be represented as a map with two entries, the keys being the xs:boolean value true for the real part, and the xs:boolean value false for the imaginary part. A library for manipulation of complex numbers might include functions such as the following:

<xsl:variable name="REAL" static="yes" as="xs:int" select="0"/> 
<xsl:variable name="IMAG" static="yes" as="xs:int" select="1"/> 
                     
<xsl:function name="i:complex" as="map(xs:int, xs:double)">
  <xsl:param name="real" as="xs:double"/>
  <xsl:param name="imaginary" as="xs:double"/>
  <xsl:sequence select="map{ $REAL : $real, $IMAG : $imaginary }"/>
</xsl:function>

<xsl:function name="i:real" as="xs:double">
  <xsl:param name="complex" as="map(xs:int, xs:double)"/>
  <xsl:sequence select="$complex($REAL)"/>
</xsl:function>

<xsl:function name="i:imaginary" as="xs:double">
  <xsl:param name="complex" as="map(xs:int, xs:double)"/>
  <xsl:sequence select="$complex($IMAG)"/>
</xsl:function>

<xsl:function name="i:add" as="map(xs:int, xs:double)">
  <xsl:param name="arg1" as="map(xs:int, xs:double)"/>
  <xsl:param name="arg2" as="map(xs:int, xs:double)"/>
  <xsl:sequence select="i:complex(i:real($arg1)+i:real($arg2), 
                                  i:imaginary($arg1)+i:imaginary($arg2)"/>
</xsl:function>

<xsl:function name="i:multiply" as="map(xs:boolean, xs:double)">
  <xsl:param name="arg1" as="map(xs:boolean, xs:double)"/>
  <xsl:param name="arg2" as="map(xs:boolean, xs:double)"/>
  <xsl:sequence select="i:complex(
      i:real($arg1)*i:real($arg2) - i:imaginary($arg1)*i:imaginary($arg2),
      i:real($arg1)*i:imaginary($arg2) + i:imaginary($arg1)*i:real($arg2))"/>
</xsl:function>

 

Example: Using a Map as an Index

Given a set of book elements, it is possible to construct an index in the form of a map allowing the books to be retrieved by ISBN number.

Assume the book elements have the form:

<book>
  <isbn>0470192747</isbn>
  <author>Michael H. Kay</author>
  <publisher>Wiley</publisher>
  <title>XSLT 2.0 and XPath 2.0 Programmer's Reference</title>
</book>

An index may be constructed as follows:

<xsl:variable name="isbn-index" as="map(xs:string, element(book))"
    select="map:new(for $b in //book return map{$b/isbn : $b})"/>

This index may then be used to retrieve the book for a given ISBN using either of the expressions map:get($isbn-index, "0470192747") or $isbn-index("0470192747").

In this simple form, this replicates the functionality available using xsl:key and the key function. However, it also provides capabilities not directly available using the key function: for example, the index can include book elements in multiple source documents. It also allows processing of all the books using a construct such as <xsl:for-each select="map:keys($isbn-index)">

 

Example: A Map containing Named Functions

As in JavaScript, a map whose keys are strings and whose associated values are function items can be used in a similar way to a class in object-oriented programming languages.

Suppose an application needs to handle customer order information that may arrive in three different formats, with different hierarchic arrangements:

  1. Flat structure:

    <customer id="c123">...</customer>
    <product id="p789">...</product>
    <order customer="c123" product="p789">...</order>
    
  2. Orders within customer elements:

    <customer id="c123">
       <order product="p789">...</order>
    </customer>
    <product id="p789">...</product>
    
  3. Orders within product elements:

    <customer id="c123">...</customer>
    <product id="p789">
      <order customer="c123">...</order>
    </product>
    

An application can isolate itself from these differences by defining a set of functions to navigate the relationships between customers, orders, and products: orders-for-customer, orders-for-product, customer-for-order, product-for-order. These functions can be implemented in different ways for the three different input formats. For example, with the first format the implementation might be:

<xsl:variable name="flat-input-functions" as="map(xs:string, function(*))*"
  select="map{
            'orders-for-customer' : 
                 function($c as element(customer)) as element(order)* 
                    {$c/../order[@customer=$c/@id]},
            'orders-for-product' : 
                 function($p as element(product)) as element(order)* 
                    {$p/../order[@product=$p/@id]},
            'customer-for-order' : 
                 function($o as element(order)) as element(customer) 
                    {$o/../customer[@id=$o/@customer]},
            'product-for-order' : 
                 function($o as element(order)) as element(product) 
                    {$o/../product[@id=$o/@product]} }                    
         "/>

Having established which input format is in use, the application can bind the appropriate implementation of these functions to a variable such as $input-navigator, and can then process the input using XPath expressions such as the following, which selects all products for which there is no order: //product[empty($input-navigator("orders-for-product")(.))]

21.2 Processing JSON Data

JSON is a popular format for exchange of structured data on the web: it is specified in [RFC 4627] and in [ECMA-404]. This section describes facilities allowing JSON data to be processed using XSLT.

21.2.1 XML Representation of JSON

This specification defines a mapping from JSON data to XML (specifically, to XDM instances). A function json-to-xml is provided to take a JSON string as input and convert it to the XML representation. Two stylesheet modules are provided to perform the reverse transformation: one produces JSON in compact linear form, the other in indented form suitable for display, editing, or printing.

The XML representation is designed to be capable of representing any valid JSON text other than one that uses characters which are not valid in XML. The transformation is lossless: that is, distinct JSON texts convert to distinct XML representations. When converting JSON to XML, options are provided to reject unsupported characters, to replace them with a substitute character, or to leave them in backslash-escaped form.

The following example demonstrates the correspondence of a JSON text and the corresponding XML representation.

Example: A JSON Text and its XML Representation

Consider the following JSON text:

  { "first name" : "John",
    "last name" : "Smith",
    "retired" : true,
    "address" :  {
       "street address" : "21 2nd Street",
       "city" : "New York",
       "state" : "NY",
       "postal code" : 10021 
    }, 
    "phone numbers" :  [ 
       { "home": "212 732-1234", 
         "fax": "646 123-4567"
       }
     ],
    "date of birth" : null
  }
               

The XML representation of this text is as follows. Whitespace is included in the XML representation for purposes of illustration, and is ignored by the stylesheets that convert XML to JSON, but it will not be present in the output of the json-to-xml function.

  <map xmlns="http://www.w3.org/2013/XSL/json">
    <string key='first name'>John</string>
    <string key='last name'>Smith</string>
    <boolean key="retired">true</boolean>
    <map key='address'>
        <string key='street address'>21 2nd Street</string>
        <string key='city'>New York</string>
        <string key='state'>NY</string>
        <number key='postal code'>10021</number>        
    </map>
    <array key='phone numbers'>
        <map>
            <string key="home">212 732-1234</string>
            <string key="fax">646 123-4567</string>
        </map>    
    </array>
    <null key="date of birth"/>
</map>                
                  
               

An XSD 1.0 schema for the XML representation is provided in B.1 Schema for the XML Representation of JSON. It is not necessary to import this schema (using xsl:import-schema) unless the stylesheet makes explicit reference to the components defined in the schema. If the stylesheet does import a schema for the namespace http://www.w3.org/2013/XSL/json, then:

  1. The processor (if it is schema-aware) must recognize an xsl:import-schema declaration for this namespace, whether or not the schema-location is supplied.

  2. If a schema-location is provided, then the schema document at that location must be equivalent to the schema document at B.1 Schema for the XML Representation of JSON; the effect if it is not is implementation-defined

The rules governing the mapping from JSON to XML are as follows. In these rules, the term "an element named N" is to be interpreted as meaning "an element node whose local name is N and whose namespace URI is http://www.w3.org/2013/XSL/json"

  1. The JSON value null is represented by an element named null, with empty content.

  2. The JSON values true and false are represented by an element named boolean, with content conforming to the type xs:boolean.

  3. A JSON number is represented by an element named number, with content conforming to the type xs:double, with the additional restriction that the value must not be positive or negative infinity, nor NaN.

  4. A JSON string is represented by an element named string, with content conforming to the type xs:string.

  5. A JSON array is represented by an element named array. The content is a sequence of child elements representing the members of the array in order, each such element being the representation of the array member obtained by applying these rules recursively.

  6. A JSON object is represented by an element named map. The content is a sequence of child elements each of which represents one of the name/value pairs in the object. The representation of the name/value pair N:V is obtained by taking the element that represents the value V (by applying these rules recursively) and adding an attribute with name key (in no namespace), whose value is N as an instance of xs:string.

The attribute escaped="true" may be specified on a string element to indicate that the string value contains backslash-escaped characters that are to be interpreted according to the JSON rules. The attribute escaped-key="true" may be specified on any element with a key attribute to indicate that the key value contains backslash-escaped characters that are to be interpreted according to the JSON rules. Both attributes have the default value false.

Although the order of entries in a JSON object is generally considered to have no significance, the function json-to-xml and the stylesheets that perform the reverse transformation both retain order.

The XDM representation of a JSON value may either be untyped (all elements annotated as xs:untyped, attributes as xs:untypedAtomic), or it may be typed. If it is typed, then it must have the type annotations obtained by validating the untyped representation against the schema given in B.1 Schema for the XML Representation of JSON. If it is untyped, then it must be an XDM instance such that validation against this schema would succeed.

21.2.2 fn:json-to-xml

Summary

Parses a string supplied in the form of a JSON text, returning the results in the form of an XML document node.

Signatures

json-to-xml($json-text as xs:string) as document-node()
json-to-xml( $json-text  as xs:string,
$options  as map(*)) as document-node()
Properties

This function is deterministicFO30, context-dependentFO30, and focus-independentFO30. It depends on static base uri.

Rules

The effect of the one-argument form of this function is the same as calling the two-argument form with an empty map as the value of the $options argument.

The first argument is a JSON-text (see below) in the form of a string. The function parses this string to return an XDM node.

The $options argument can be used to control the way in which the parsing takes place. The value of the argument is a map. The options defined in this specification have keys that are strings. The effect of any map entries whose keys are not defined in this specification is implementation-defined; implementation-defined options should use QNames as keys. Implementations must ignore any entries in the map whose keys are not defined in this specification, unless the key has a specific implementation-defined meaning.

The entries that may appear in the $options map are as follows. The keys are xs:string values:

Key Value Meaning
spec Determines the specification of JSON that is to be used. The value must be a string; the effect of supplying any value other than "RFC4627", "ECMA-404", or "liberal" is implementation-defined. The default is "RFC4627".
"RFC4627" The input must conform to [RFC 4627], with no deviations from the grammar permitted.
"ECMA-404" The input must conform to the specification in "ECMA-404".
"liberal" Indicates any implementation-defined superset of RFC4627 (or equivalently, an implementation that recovers from some or all errors in the input).
validate If the $options map contains an entry with the key "validate", then the value must be an xs:boolean. The default is true for a schema-aware processor, false for a non-schema-aware processor. If the value true is supplied and the processor is not schema-aware, a dynamic error results [see ERR XTDE3245]. It is not necessary that the containing stylesheet should import the relevant schema.
true Indicates that the resulting XDM instance must be typed; that is, the element and attribute nodes must carry the type annotations that result from validation against the schema given at B.1 Schema for the XML Representation of JSON, or against an implementation-defined schema if the spec option has the value liberal.
false Indicates that the the XDM instance must be untyped.
unescape If the $options map contains an entry with the key "unescape", then the value must be an xs:boolean. The value determines whether escape sequences (marked by a backslash) in the input are expanded. The default is true.
false In the result, any string element whose string value contains a backslash character must have the attribute value escaped="true", and any element that contains a key attribute whose string value contains a backslash character must have the attribute escaped-key="true". (The value of the escaped and key-escaped attributes is immaterial when there is no backslash present, and it is never necessary to include either attribute when the value is false.) The escaped representation in this case may be used for any character, whether or not it was escaped in the original JSON input.
true The attributes escaped and escaped-key will never be present with the value true. If the input contains escape sequences representing characters or codepoints that are not valid characters in the version of XML supported by the implementation, such characters are replaced by the Unicode replacement character (xFFFD), or as described in the next paragraph.
fallback Provides a function which is called when an invalid character is encountered.
Function with signature function(xs:string) as xs:string When an invalid character is encountered this function is called supplying the escaped form of the character as the argument. The function returns a string which is inserted into the result in place of the invalid character. The function also has the option of raising a dynamic error.

The various structures that can occur in JSON are transformed recursively to XDM values according to the rules given in 21.2.1 XML Representation of JSON.

The function returns a document node, whose only child is the element node representing the outermost construct in the JSON text.

The function is not : that is, if the function is called twice with the same arguments, it is implementation-dependent whether the same node is returned on both occasions.

The base URI of the returned document node is taken from the static base URI of the function call.

Error Conditions

[ERR XTDE3240] It is a dynamic error if the value of $input does not conform to the JSON grammar, as selected using the explicit or implicit spec option.

[ERR XTDE3245] It is a dynamic error if the value of the validate option is true and the processor is not schema-aware.

[ERR XTDE3250] It is a dynamic error if the value of $input contains an escaped representation of a character (or codepoint) that is not a valid character in the version of XML supported by the implementation, unless the unescape option is set to false.

[ERR XTDE3260] It is a dynamic error if the value of $options includes an entry whose key is "spec" and whose value is not a single xs:string, or an entry whose key is "validate" or "unescape" and whose value is not a single xs:boolean.

Notes

To read a JSON file, this function can be used in conjunction with the unparsed-textFO30 function.

ECMA-404 differs from RFC 4627 in two respects: it does not allow the input to depart from the JSON grammar, but it does allow the top-level construct in the input to be a string, boolean, number, or null, rather than requiring an object or array.

Many JSON implementations allow commas to be used after the last item in an object or array, although the specification does not permit it. The option spec="liberal" is provided to allow such deviations from the specification to be accepted. Some JSON implementations also allow constructors such as new Date("2000-12-13") to appear as values: specifying spec="liberal" allows such extensions to be accepted, but does not guarantee it. If such extensions are accepted, the resulting value is implementation-defined, and will not necessarily conform to the schema at B.1 Schema for the XML Representation of JSON.

Examples

The expression json-to-xml('{"x": 1, "y": [3,4,5]}') returns <map xmlns="http://www.w3.org/2013/XSL/json"> <number key="x">1</number> <array key="y"> <number>3</number> <number>4</number> <number>5</number> </array> </map>.

The expression json-to-xml('"abcd"', map{'spec': 'RFC4627'}) raises error FOJS0001. (This is an error because RFC4627 requires the outermost construct in JSON to be an array or object, not a string.).

The expression json-to-xml('"abcd"', map{'spec': 'ECMA-404'}) returns <string xmlns="http://www.w3.org/2013/XSL/json">abcd</string>.

The expression json-to-xml('{"x": "\\", "y": "\u0025"}') returns one of the following: <map xmlns="http://www.w3.org/2013/XSL/json"> <string key="x">\</string> <string key="y">%</string> </map> or map{"x": "\","y": "%"}.

The expression json-to-xml('{"x": "\\", "y": "\u0025"}', map{'unescape': false()}) returns <map xmlns="http://www.w3.org/2013/XSL/json"> <string escaped="true" key="x">\\</string> <string escaped="true" key="y">\u0025</string> </map>.

The following example illustrates use of the fallback function to handle characters that are invalid in XML.

 <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                xmlns:err="http://example.com/ns/errors"
                xmlns:f="http://example.com/ns/functions"
                xmlns:xs="http://www.w3.org/2001/XMLSchema"
                exclude-result-prefixes="xs err f"
                version="3.0">

<xsl:template match="someElement">
  <xsl:variable name="jsonstr" 
                select="unparsed-text('http://example.com/endpoint')"/>
  <xsl:variable name="options" 
                select="map{'spec':'liberal', 'fallback':f:convert#1}"/>
  <xsl:variable name="json" 
                select="json-to-xml($jsonstr, $options)"/>

  <!-- now do something with that json -->
</xsl:template>

<xsl:function name="f:convert" as="xs:string">
  <xsl:param name="char" as="xs:string"/>
    <xsl:variable name="c0chars" select="{
     '\u0000':'[NUL]',
     '\u0001':'[SOH]',
     '\u0002':'[STX]',
     ...
     '\u001E':'[RS]',
     '\u001F':'[US]'}"/>
  <xsl:variable name="replacement" select="$c0chars($char)"/>
  <xsl:sequence select="if (exists($replacement)) then $replacement
      else error(xs:QName('err:invalid-char'), 
           'Error: '||$char||' is not a terminal control char.'))"/>
</xsl:function>
</xsl:stylesheet>

21.2.3 Converting XML to JSON

Two stylesheets are provided whose effect is to convert the XML representation of JSON defined in 21.2.1 XML Representation of JSON to a string conforming to the JSON grammar. The stylesheets are listed in B XML Representation of JSON. They are presented as separate packages which may be incorporated into a user stylesheet using xsl:use-package.

The first stylesheet, xml-to-json.xsl, produces a JSON string containing minimal whitespace. The second, xml-to-json-indented.xsl, produces a JSON string with whitespace indentation designed for human legibility.

The stylesheets are designed to be configurable by setting parameter values or by overriding selected template rules or functions.

The stylesheets define the punctuation characters of JSON as parameters which can be overridden. This is intended to allow the stylesheets to be adapted to produce map literals suitable for use in other languages (PHP, for example, uses "=>" rather than ":" to separate keys from values). Setting the punctuation characters can also be used to alter the amount of whitespace in the result.

The conversion can be effected either by calling the public function j:xml-to-json, which takes an XML node as its argument and produces the JSON string as its output, or by applying templates to the XML node in mode j:xml-to-json: this delivers a sequence of text nodes, which may be processed for example using:

<xsl:variable name="json">
  <xsl:apply-templates select="$json-as-xml"/>
</xsl:variable>

or:

<xsl:result-document href="output.json" method="text">
  <xsl:apply-templates select="$json-as-xml"/>
</xsl:result-document>

The stylesheets do not validate that the input conforms to the schema defined at B.1 Schema for the XML Representation of JSON, and the effect of using them with input that does not conform to this schema is unpredictable.

22 Diagnostics

22.1 Messages

<!-- Category: instruction -->
<xsl:message
  select? = expression
  terminate? = { "yes" | "no" }
  error-code? = { eqname } >
  <!-- Content: sequence-constructor -->
</xsl:message>

The xsl:message instruction sends a message in an implementation-defined way. The xsl:message instruction causes the creation of a new document, which is typically serialized and output to an implementation-defined destination. The result of the xsl:message instruction is an empty sequence.

The content of the message may be specified by using either or both of the optional select attribute and the sequence constructor that forms the content of the xsl:message instruction.

If the xsl:message instruction contains a sequence constructor, then the sequence obtained by evaluating this sequence constructor is used to construct the content of the new document node, as described in 5.8.1 Constructing Complex Content.

If the xsl:message instruction has a select attribute, then the value of the attribute must be an XPath expression. The effect of the xsl:message instruction is then the same as if a single xsl:copy-of instruction with this select attribute were added to the start of the sequence constructor.

If the xsl:message instruction has no content and no select attribute, then an empty message is produced.

The tree produced by the xsl:message instruction is not technically a final result tree. The tree has no URI and processors are not required to make the tree accessible to applications.

Note:

In many cases, the XML document produced using xsl:message will consist of a document node owning a single text node. However, it may contain a more complex structure.

Note:

An implementation might implement xsl:message by popping up an alert box or by writing to a log file. Because the order of execution of instructions is implementation-defined, the order in which such messages appear is not predictable.

The terminate attribute is interpreted as an attribute value template.

If the effective value of the terminate attribute is yes, then the processor must signal a dynamic error after sending the message. This error may be caught in the same way as any other dynamic error using xsl:catch. The default value is no. Note that because the order of evaluation of instructions is implementation-dependent, this gives no guarantee that any particular instruction will or will not be evaluated before processing terminates.

The optional error-code attribute may be used to indicate the error code associated with the message. This may be used irrespective of the value of terminate. The error code is an EQName. If no error code is specified, or if the value is not a valid EQName, the error code will have local part XTMM9000 and namespace URI http://www.w3.org/2005/xqt-errors. User-defined error codes should be in a namespace other than http://www.w3.org/2005/xqt-errors. When the value of terminate is yes, the error code may be matched in an xsl:catch element to catch the error and cause processing to continue normally.

[ERR XTMM9000] When a transformation is terminated by use of xsl:message terminate="yes", the effect is the same as when a dynamic error occurs during the transformation. The default error code is XTMM9000; this may be overridden using the error-code attribute of the xsl:message instruction.

Example: Localizing Messages

One convenient way to do localization is to put the localized information (message text, etc.) in an XML document, which becomes an additional input file to the stylesheet. For example, suppose messages for a language L are stored in an XML file resources/L.xml in the form:

<messages>
  <message name="problem">A problem was detected.</message>
  <message name="error">An error was detected.</message>
</messages>

Then a stylesheet could use the following approach to localize messages:

<xsl:param name="lang" select="'en'"/>
<xsl:variable name="messages"
  select="document(concat('resources/', $lang, '.xml'))/messages"/>

<xsl:template name="localized-message">
  <xsl:param name="name"/>
  <xsl:message select="string($messages/message[@name=$name])"/>
</xsl:template>

<xsl:template name="problem">
  <xsl:call-template name="localized-message">
    <xsl:with-param name="name">problem</xsl:with-param>
  </xsl:call-template>
</xsl:template>

Any dynamic error that occurs while evaluating the select expression or the contained sequence constructor, and any serialization error that occurs while processing the result, does not cause the transformation to fail; at worst, it means that no message is output, or that the only message that is output is one that relates to the error that occurred..

Note:

An example of such an error is the serialization error that occurs when processing the instruction <xsl:message select="@code"/> (on the grounds that free-standing attributes cannot be serialized). Making such errors recoverable means that it is implementation-defined whether or not they are signaled to the user and whether they cause termination of the transformation. If the processor chooses to recover from the error, the content of any resulting message is implementation-dependent.

One possible recovery action is to include a description of the error in the generated message text.

22.2 Assertions

The xsl:assert instruction is used to assert that the value of a particular expression is true; if the value of the expression is false, and assertions are enabled, then a dynamic error occurs.

<!-- Category: instruction -->
<xsl:assert
  test = expression
  select? = expression
  error-code? = { eqname } >
  <!-- Content: sequence-constructor -->
</xsl:assert>

By default, assertions are enabled. Checking of assertions may be disabled in several ways:

  1. As with any other instruction, assertions may be disabled by use of the use-when attribute: see 3.14 Conditional Element Inclusion.

  2. An implementation should provide an external mechanism to disable assertion checking for the stylesheet as a whole (either statically or dynamically). The detail of such mechanisms is implementation-defined.

If assertion checking is enabled, the instruction is evaluated as follows:

  1. The expression in the test attribute is evaluated. If the effective boolean value of the result is true, the assertion succeeds, and no further action is taken. If the effective boolean value is false, or if a dynamic error occurs during evaluation of the expression, then the assertion fails.

  2. If the assertion fails, then the effect of the instruction is governed by the rules for evaluation of an xsl:message instruction with the same select attribute, error-code attribute, and contained sequence constructor, and with the value terminate="yes". However, the default error code if the error-code attribute is omitted is XTMM9001 rather than XTMM9000.

    Note:

    To the extent that the behavior of xsl:message is implementation-defined, this rule does not prevent an implementation treating xsl:assert and xsl:message differently.

[ERR XTMM9001] When a transformation is terminated by use of xsl:assert, the effect is the same as when a dynamic error occurs during the transformation. The default error code is XTMM9001; this may be overridden using the error-code attribute of the xsl:assert instruction.

As with any other dynamic error, an error caused by an assertion failing may be trapped using xsl:try: see 8.3 Try/Catch.

The result of the xsl:assert instruction is an empty sequence.

Example: Using Assertions with Static Parameters

The following example shows a stylesheet function that checks that the value of its supplied argument is in range. The check is performed only if the static parameter $DEBUG is set to true.

<xsl:param name="DEBUG" as="xs:boolean" select="false()" 
           static="yes" required="no"/>
<xsl:function name="f:days-elapsed" as="xs:integer">
  <xsl:param name="date" as="xs:date"/>
  <xsl:assert use-when="$DEBUG" test="$date lt current-date()"/>
  <xsl:sequence select="(current-date() - $since) 
                            div xs:dayTimeDuration('PT1D')"/>
</xsl:function>

Note:

Implementations should avoid optimizing xsl:assert instructions away. As a guideline, if the result of a sequence constructor is required by the transformation, the implementation should ensure that all xsl:assert instructions in that sequence constructor are evaluated. Conversely, if the result of a sequence constructor is not required by the transformation, its xsl:assert instructions should not be evaluated.

This recommendation is not intended to prevent optimizations such as lazy evaluation, where evaluation of a sequence constructor may finish early, as soon as enough information is available to evaluate the containing instruction.

An implementation may provide a user option allowing a processor to treat assertions as being true without explicit checking. This option must not be enabled by default. If such an option is in force, the effect of any assertion not being true is implementation-dependent.

Note:

For example, given the assertion <xsl:assert test="count(//title)=1"/>, a processor might generate code for the expression <xsl:value-of select="//title"/> that stops searching for title elements after finding the first one. In the event that the source document contains more than one title, execution of the stylesheet may fail in arbitrary ways, or it may produce incorrect output.

23 Extensibility and Fallback

XSLT allows two kinds of extension, extension instructions and extension functions.

[Definition: An extension instruction is an element within a sequence constructor that is in a namespace (not the XSLT namespace) designated as an extension namespace.]

[Definition: An extension function is a function that is available for use within an XPath expression, other than a core function defined in [Functions and Operators], an additional function defined in this XSLT specification, a constructor function named after an atomic type, or a stylesheet function defined using an xsl:function declaration.].

This specification does not define any mechanism for creating or binding implementations of extension instructions or extension functions, and it is not required that implementations support any such mechanism. Such mechanisms, if they exist, are implementation-defined. Therefore, an XSLT stylesheet that must be portable between XSLT implementations cannot rely on particular extensions being available. XSLT provides mechanisms that allow an XSLT stylesheet to determine whether the implementation makes particular extensions available, and to specify what happens if those extensions are not available. If an XSLT stylesheet is careful to make use of these mechanisms, it is possible for it to take advantage of extensions and still retain portability.

23.1 Extension Functions

The set of functions that can be called from a FunctionCallXP30 within an XPath expression may include one or more extension functions. The expanded QName of an extension function always has a non-null namespace URI.

23.1.1 fn:function-available

Summary

Determines whether a particular function is or is not available for use. The function is particularly useful for calling within an [xsl:]use-when attribute (see 3.14 Conditional Element Inclusion) to test whether a particular extension function is available.

Signatures

function-available($function-name as xs:string) as xs:boolean
function-available( $function-name  as xs:string,
$arity  as xs:integer) as xs:boolean
Properties

This function is deterministicFO30, context-dependentFO30, and focus-independentFO30. It depends on namespaces, and known function signatures.

Rules

A function is said to be available within an XPath expression if it is present in the statically known function signaturesXP30 for that expression (see 5.4.1 Initializing the Static Context). Functions in the static context are uniquely identified by the name of the function (a QName) in combination with its arity.

The value of the $function-name argument must be a string containing a EQName. The lexical QName is expanded into an expanded QName using the namespace declarations in scope for the expression. If the value is an unprefixed lexical QName, then the standard function namespace is used in the expanded QName.

The two-argument version of the function-available function returns true if and only if there is an available function whose name matches the value of the $function-name argument and whose arity matches the value of the $arity argument.

The single-argument version of the function-available function returns true if and only if there is at least one available function (with some arity) whose name matches the value of the $function-name argument.

When the containing expression is evaluated with XPath 1.0 compatibility mode set to true, the function-available function returns false in respect of a function name and arity for which no implementation is available (other than the fallback error function that raises a dynamic error whenever it is called). This means that it is possible (as in XSLT 1.0) to use logic such as the following to test whether a function is available before calling it:

Example: Calling an extension function with backwards compatibility enabled
<summary xsl:version="1.0">
  <xsl:choose>
    <xsl:when test="function-available('my:summary')">
      <xsl:value-of select="my:summary()"/>
    </xsl:when>
    <xsl:otherwise>
      <xsl:text>Summary not available</xsl:text>
    </xsl:otherwise>
  </xsl:choose>
</summary>
Error Conditions

[ERR XTDE1400] It is a dynamic error if the argument does not evaluate to a string that is a valid EQName, or if the value is a lexical QName with a prefix for which no namespace declaration is present in the static context. If the processor is able to detect the error statically (for example, when the argument is supplied as a string literal), then the processor may optionally signal this as a static error.

Notes

The fact that a function with a given name is available gives no guarantee that any particular call on the function will be successful. For example, it is not possible to determine the types of the arguments expected.

The introduction of the function-lookupFO30 function in XPath 3.0 reduces the need for function-available, since function-lookupFO30 not only tests whether a function is available, but also returns a function item that enables it to be dynamically called.

If a function is present in the static context but with no useful functionality (for example, if the system has been configured for security reasons so that available-environment-variablesFO30 returns no information), then function-available when applied to that function should return false.

It is not necessary that there be a direct equivalence between the results of function-available anr function-lookupFO30 in all cases. For example, there may be extension functions whose side-effects are such that for security reasons, dynamic calls to the function are disallowed; function-lookupFO30 might then not provide access to the function. The main use-case for function-available, by contrast, is for use in [xsl:]use-when conditions to test whether static calls on the function are possible.

Examples
Example: Stylesheet portable between XSLT 1.0, XSLT 2.0, and XSLT 3.0

A stylesheet that is designed to use XSLT 2.0 facilities when running under an XSLT 2.0 or XSLT 3.0 processor, but to fall back to XSLT 1.0 capabilities when not, might be written using the code:

<out xsl:version="2.0">
  <xsl:choose>
    <xsl:when test="function-available('matches')">
      <xsl:value-of select="matches(/doc/title, '[a-z]*')"/>
    </xsl:when>
    <xsl:otherwise>
      <xsl:value-of select="string-length(
                translate(/doc/title, 'abcdefghijklmnopqrstuvwxyz', '')) = 0"/>
    </xsl:otherwise>
  </xsl:choose>
</out>

Here an XSLT 2.0 or XSLT 3.0 processor will always take the xsl:when branch, while a 1.0 processor will follow the xsl:otherwise branch. The single-argument version of the function-available function is used here, because that is the only version available in XSLT 1.0. Under the rules of XSLT 1.0, the call on the matches function is not an error, because it is never evaluated.

 

Example: Stylesheet portable between XSLT 3.0 and a future version of XSLT

A stylesheet that is designed to use facilities in some future XSLT version when they are available, but to fall back to XSLT 2.0 or XSLT 3.0 capabilities when not, might be written using code such as the following. This hypothesizes the availability in some future version of a function pad which pads a string to a fixed length with spaces:

 <xsl:value-of select="pad(/doc/title, 10)" 
               use-when="function-available('pad', 2)"/>
 <xsl:value-of select="concat(/doc/title, string-join(
                          for $i in 1 to 10 - string-length(/doc/title) 
                                                  return ' ', ''))"
               use-when="not(function-available('pad', 2))"/>
 

In this case the two-argument version of function-available is used, because there is no requirement for this code to run under XSLT 1.0.

23.1.2 Calling Extension Functions

If the function name used in a FunctionCallXP30 within an XPath expression identifies an extension function, then to evaluate the FunctionCallXP30, the processor will first evaluate each of the arguments in the FunctionCallXP30. If the processor has information about the datatypes expected by the extension function, then it may perform any necessary type conversions between the XPath datatypes and those defined by the implementation language. If multiple extension functions are available with the same name, the processor may decide which one to invoke based on the number of arguments, the types of the arguments, or any other criteria. The result returned by the implementation is returned as the result of the function call, again after any necessary conversions between the datatypes of the implementation language and those of XPath. The details of such type conversions are outside the scope of this specification.

[ERR XTDE1420] It is a dynamic error if the arguments supplied to a call on an extension function do not satisfy the rules defined for that particular extension function, or if the extension function reports an error, or if the result of the extension function cannot be converted to an XPath value.

Note:

Implementations may also provide mechanisms allowing extension functions to report recoverable dynamic errors, or to execute within an environment that treats some or all of the errors listed above as recoverable.

[ERR XTDE1425] When the containing element is processed with XSLT 1.0 behavior, it is a dynamic error to evaluate an extension function call if no implementation of the extension function is available.

Note:

When XSLT 1.0 behavior is not enabled, this is a static error [ERR XPST0017] XP30.

Note:

There is no prohibition on calling extension functions that have side-effects (for example, an extension function that writes data to a file). However, the order of execution of XSLT instructions is not defined in this specification, so the effects of such functions are unpredictable.

Implementations are not required to perform full validation of values returned by extension functions. It is an error for an extension function to return a string containing characters that are not permitted in XML, but the consequences of this error are implementation-defined. The implementation may raise an error, may convert the string to a string containing valid characters only, or may treat the invalid characters as if they were permitted characters.

Note:

The ability to execute extension functions represents a potential security weakness, since untrusted stylesheets may invoke code that has privileged access to resources on the machine where the processor executes. Implementations may therefore provide mechanisms that restrict the use of extension functions by untrusted stylesheets.

All observations in this section regarding the errors that can occur when invoking extension functions apply equally when invoking extension instructions.

23.1.3 External Objects

An implementation may allow an extension function to return an object that does not have any natural representation in the XDM data model, whether as an atomic value, a node, or a function item. For example, an extension function sql:connect might return an object that represents a connection to a relational database; the resulting connection object might be passed as an argument to calls on other extension functions such as sql:insert and sql:select.

The way in which such objects are represented in the type system is implementation-defined. They might be represented by a completely new datatype, or they might be mapped to existing datatypes such as integer, string, or anyURI.

23.1.4 fn:type-available

Summary

Used to control how a stylesheet behaves if a particular schema type is or is not available in the static context.

Signature

type-available($type-name as xs:string) as xs:boolean
Properties

This function is deterministicFO30, context-dependentFO30, and focus-independentFO30. It depends on namespaces, and schema definitions.

Rules

A schema type (that is, a simple type or a complex type) is said to be available within an XPath expression if it is a type definition that is present in the in-scope schema typesXP30 for that expression (see 5.4.1 Initializing the Static Context). This includes built-in types, types imported using xsl:import-schema, and extension types defined by the implementation.

The value of the $type-name argument must be a string containing a EQName. The EQName is expanded into an expanded QName using the namespace declarations in scope for the expression. If the value is an unprefixed lexical QName, then the default namespace is used in the expanded QName.

The function returns true if and only if there is an available type whose name matches the value of the $type-name argument.

Error Conditions

[ERR XTDE1428] It is a dynamic error if the argument does not evaluate to a string that is a valid EQName, or if the value is a lexical QName with a prefix for which no namespace declaration is present in the static context. If the processor is able to detect the error statically (for example, when the argument is supplied as a string literal), then the processor may optionally signal this as a static error.

Notes

The type-available function is of limited use within an [xsl:]use-when expression, because the static context for the expression does not include any user-defined types.

23.2 Extension Instructions

[Definition: The extension instruction mechanism allows namespaces to be designated as extension namespaces. When a namespace is designated as an extension namespace and an element with a name from that namespace occurs in a sequence constructor, then the element is treated as an instruction rather than as a literal result element.] The namespace determines the semantics of the instruction.

Note:

Since an element that is a child of an xsl:stylesheet element is not occurring in a sequence constructor , user-defined data elements (see 3.8.3 User-defined Data Elements) are not extension elements as defined here, and nothing in this section applies to them.

23.2.1 Designating an Extension Namespace

A namespace is designated as an extension namespace by using an [xsl:]extension-element-prefixes attribute on an element in the stylesheet (see 3.5 Standard Attributes). The attribute must be in the XSLT namespace only if its parent element is not in the XSLT namespace. The value of the attribute is a whitespace-separated list of namespace prefixes. The namespace bound to each of the prefixes is designated as an extension namespace.

The default namespace (as declared by xmlns) may be designated as an extension namespace by including #default in the list of namespace prefixes.

[ERR XTSE1430] It is a static error if there is no namespace bound to the prefix on the element bearing the [xsl:]extension-element-prefixes attribute or, when #default is specified, if there is no default namespace.

The designation of a namespace as an extension namespace is effective for the element bearing the [xsl:]extension-element-prefixes attribute and for all descendants of that element within the same stylesheet module.

23.2.2 fn:element-available

Summary

Determines whether a particular instruction is or is not available for use. The function is particularly useful for calling within an [xsl:]use-when attribute (see 3.14 Conditional Element Inclusion) to test whether a particular extension instruction is available.

Signature

element-available($element-name as xs:string) as xs:boolean
Properties

This function is deterministicFO30, context-dependentFO30, and focus-independentFO30. It depends on namespaces.

Rules

The value of the $element-name argument must be a string containing an EQName. If it is a lexical QName with a prefix, the it is expanded into an expanded QName using the namespace declarations in the static context of the expression. If there is a default namespace in scope, then it is used to expand an unprefixed lexical QName.

If the resulting expanded QName is in the XSLT namespace, the function returns true if and only if the local name matches the name of an XSLT element that is defined in this specification and implemented by the XSLT processor.

If the expanded QName has a null namespace URI, the element-available function will return false.

If the expanded QName is not in the XSLT namespace, the function returns true if and only if the processor has an implementation available of an extension instruction with the given expanded QName. This applies whether or not the namespace has been designated as an extension namespace.

If the processor does not have an implementation of a particular extension instruction available, and such an extension instruction is evaluated, then the processor must perform fallback for the element as specified in 23.2.3 Fallback. An implementation must not signal an error merely because the stylesheet contains an extension instruction for which no implementation is available.

Error Conditions

[ERR XTDE1440] It is a dynamic error if the argument does not evaluate to a string that is a valid EQName, or if the value is a lexical QName with a prefix for which no namespace declaration is present in the static context. If the processor is able to detect the error statically (for example, when the argument is supplied as a string literal), then the processor may optionally signal this as a static error.

Notes

For element names in the XSLT namespace:

  • Where conformance rules make some features of the specification optional, for example the xsl:stream element, this function can be used (typically in a use-when expression) to determine whether the feature is available in a particular processor. It can also be useful to distinguish processors that implement XSLT 3.0 from processors that implement other (older or newer) versions of the specification, and to distinguish full implementations from incomplete implementations.

  • In earlier versions of this specification, element-available was defined to return true only for elements classified as instructions. The distinction between instructions and other elements, however, is sometimes rather technical, and in XSLT 3.0 the effect of the function has therefore been aligned to do what its name might suggest.

  • If an instruction is recognized but offers no useful functionality (for example, if the system has been configured for security reasons so that xsl:evaluate always raises an error), then element-available when applied to that instruction should return false.

For element names in other namespaces:

  • The result of the element-available does not depend on whether or not the namespace of the supplied instruction name has been designated as an extension element namespace; it tests whether the instruction would be available if the namespace were designated as such.

23.2.3 Fallback

<!-- Category: instruction -->
<xsl:fallback>
  <!-- Content: sequence-constructor -->
</xsl:fallback>

The content of an xsl:fallback element is a sequence constructor, and when performing fallback, the value returned by the xsl:fallback element is the result of evaluating this sequence constructor.

When not performing fallback, evaluating an xsl:fallback element returns an empty sequence: the content of the xsl:fallback element is ignored.

There are two situations where a processor performs fallback: when an extension instruction that is not available is evaluated, and when an instruction in the XSLT namespace, that is not defined in XSLT 3.0, is evaluated within a region of the stylesheet for which forwards compatible behavior is enabled.

Note:

Fallback processing is not invoked in other situations, for example it is not invoked when an XPath expression uses unrecognized syntax or contains a call to an unknown function. To handle such situations dynamically, the stylesheet should call functions such as system-property and function-available to decide what capabilities are available.

[ERR XTDE1450] When a processor performs fallback for an extension instruction that is not recognized, if the instruction element has one or more xsl:fallback children, then the content of each of the xsl:fallback children must be evaluated; it is a dynamic error if it has no xsl:fallback children.

Note:

This is different from the situation with unrecognized XSLT elements. As explained in 3.11 Forwards Compatible Processing, an unrecognized XSLT element appearing within a sequence constructor is a static error unless (a) forwards compatible behavior is enabled, and (b) the instruction has an xsl:fallback child.

24 Final Result Trees

The output of a transformation is a set of one or more final result trees.

A final result tree can be created explicitly, by evaluating an xsl:result-document instruction. As explained in 2.4 Executing a Transformation, a final result tree is also created implicitly if no xsl:result-document instruction is evaluated, or if the result of evaluating the initial template is a non-empty sequence.

The way in which a final result tree is delivered to an application is implementation-defined.

Serialization of final result trees is described further in 25 Serialization

24.1 Creating Final Result Trees

<!-- Category: instruction -->
<xsl:result-document
  format? = { eqname }
  href? = { uri }
  validation? = "strict" | "lax" | "preserve" | "strip"
  type? = eqname
  method? = { "xml" | "html" | "xhtml" | "text" | eqname }
  byte-order-mark? = { "yes" | "no" }
  cdata-section-elements? = { eqnames }
  doctype-public? = { string }
  doctype-system? = { string }
  encoding? = { string }
  escape-uri-attributes? = { "yes" | "no" }
  html-version? = { decimal }
  include-content-type? = { "yes" | "no" }
  indent? = { "yes" | "no" }
  item-separator? = { string }
  media-type? = { string }
  normalization-form? = { "NFC" | "NFD" | "NFKC" | "NFKD" | "fully-normalized" | "none" | nmtoken }
  omit-xml-declaration? = { "yes" | "no" }
  parameter-document? = { uri }
  standalone? = { "yes" | "no" | "omit" }
  suppress-indentation? = { eqnames }
  undeclare-prefixes? = { "yes" | "no" }
  use-character-maps? = eqnames
  output-version? = { nmtoken } >
  <!-- Content: sequence-constructor -->
</xsl:result-document>

The xsl:result-document instruction is used to create a final result tree. The content of the xsl:result-document element is a sequence constructor for the children of the document node of the tree. A document node is created, and the sequence obtained by evaluating the sequence constructor is used to construct the content of the document, as described in 5.8.1 Constructing Complex Content. The tree rooted at this document node forms the final result tree.

The xsl:result-document instruction defines the URI of the result tree, and may optionally specify the output format to be used for serializing this tree.

The effective value of the format attribute, if specified, must be a EQName. The value is expanded using the namespace declarations in scope for the xsl:result-document element. The resulting expanded QName must match the expanded QName of a named output definition in the stylesheet. This identifies the xsl:output declaration that will control the serialization of the final result tree (see 25 Serialization), if the result tree is serialized. If the format attribute is omitted, the unnamed output definition is used to control serialization of the result tree.

[ERR XTDE1460] It is a dynamic error if the effective value of the format attribute is not a valid EQName, or if it does not match the expanded QName of an output definition in the stylesheet. If the processor is able to detect the error statically (for example, when the format attribute contains no curly brackets), then the processor may optionally signal this as a static error.

Note:

The only way to select the unnamed output definition is to omit the format attribute.

The parameter-document attribute allows serialization parameters to be supplied in an external document. The external document must contain an output:serialization-parameters element with the format described in Section 3.1 Setting Serialization Parameters by Means of a Data Model Instance SER30, and the parameters are interpreted as described in that specification.

If present, the effective value of the URI supplied in the parameter-document attribute is dereferenced, after resolution against the base URI of the xsl:result-document element if it is a relative reference. If the location of the stylesheet at development time is different from the deployed location, any relative reference should be resolved against the deployed location. A serialization error occurs if the result of dereferencing the URI is ill-formed or invalid; but if no document can be found at the specified location, the attribute may be ignored.

A serialization parameter specified in the parameter-document takes precedence over a value supplied directly as an attribute of xsl:result-document, which in turn takes precedence over a value supplied in the selected output definition, except that the values of the cdata-section-elements and suppress-indentation attributes are merged in the same way as when multiple xsl:output declarations are merged.

The attributes method, byte-order-mark cdata-section-elements, doctype-public, doctype-system, encoding, escape-uri-attributes, html-version, indent, item-separator, media-type, normalization-form, omit-xml-declaration, standalone, suppress-indentation, undeclare-prefixes, use-character-maps, and output-version may be used to override attributes defined in the selected output definition.

With the exception of use-character-maps, these attributes are all defined as attribute value templates, so their values may be set dynamically. For any of these attributes that is present on the xsl:result-document instruction, the effective value of the attribute overrides or supplements the corresponding value from the output definition. This works in the same way as when one xsl:output declaration overrides another:

  • In the case of cdata-section-elements and suppress-indentation, the value of the serialization parameter is the union of the expanded names of the elements named in this instruction and the elements named in the selected output definition;

  • In the case of use-character-maps, the character maps referenced in this instruction supplement and take precedence over those defined in the selected output definition;

  • In the case of doctype-public and doctype-system, setting the effective value of the attribute to a zero-length string has the effect of overriding any value for these attributes obtained from the output definition. The corresponding serialization parameter is not set (is "absent").

  • In the case of item-separator, setting the effective value of the attribute to the special value "#absent" has the effect of overriding any value for this attribute obtained from the output definition. The corresponding serialization parameter is not set (is "absent"). it is not possible to set the value of the serialization parameter to the literal 7-character string "#absent".

  • In all other cases, the effective value of an attribute actually present on this instruction takes precedence over the value defined in the selected output definition.

Note:

In the case of the attributes method, cdata-section-elements, suppress-indentation, and use-character-maps, the effective value of the attribute contains a space-separated list of EQNames. If any of these is a lexical QName with a prefix, the prefix is expanded using the in-scope namespaces for the xsl:result-document element. In the case of cdata-section-elements and suppress-indentation, an unprefixed element name is expanded using the default namespace. In the case of the method attribute, if the method is not one of the system-defined methods (xml, html, xhtml, text) then the expanded name must have a non-absent namespace.

The output-version attribute on the xsl:result-document instruction overrides the version attribute on xsl:output (it has been renamed because version is available with a different meaning as a standard attribute: see 3.5 Standard Attributes). In all other cases, attributes correspond if they have the same name.

There are some serialization parameters that apply to some output methods but not to others. For example, the indent attribute has no effect on the text output method. If a value is supplied for an attribute that is inapplicable to the output method, its value is not passed to the serializer. The processor may validate the value of such an attribute, but is not required to do so.

The item-separator serialization parameter defined in [XSLT and XQuery Serialization] is not available in xsl:result-document; it is not applicable, because the sequence that is serialized by XSLT is always a singleton document node. Formally therefore, the serializer is invoked passing an empty string as the value of this parameter.

The href attribute is optional. The default value is the zero-length string. The effective value of the attribute must be a URI Reference, which may be absolute or relative. There may be implementation-defined restrictions on the form of absolute URI that may be used, but the implementation is not required to enforce any restrictions. Any valid relative URI reference must be accepted. Note that the zero-length string is a valid relative URI reference.

The base URI of the document node at the root of the final result tree is based on the effective value of the href attribute. If the effective value is a relative URI reference, then it is resolved relative to the base output URI. If the implementation provides an API to access final result trees, then it must allow a final result tree to be identified by means of this base URI.

Note:

The base URI of the final result tree is not necessarily the same thing as the URI of its serialized representation on disk, if any. For example, a server (or browser client) might store final result trees only in memory, or in an internal disk cache. As long as the processor satisfies requests for those URIs, it is irrelevant where they are actually written on disk, if at all.

Note:

It will often be the case that one final result tree contains links to another final result tree produced during the same transformation, in the form of a relative URI reference. The mechanism of associating a URI with a final result tree has been chosen to allow the integrity of such links to be preserved when the trees are serialized.

As well as being potentially significant in any API that provides access to final result trees, the base URI of the new document node is relevant if the final result tree, rather than being serialized, is supplied as input to a further transformation.

The optional attributes type and validation may be used on the xsl:result-document instruction to validate the contents of the new document, and to determine the type annotation that elements and attributes within the final result tree will carry. The permitted values and their semantics are described in 24.2.2 Validating Document Nodes.

A processor may allow a final result tree to be serialized. Serialization is described in 25 Serialization. However, an implementation (for example, a processor running in an environment with no access to writable filestore) is not required to support the serialization of final result trees. An implementation that does not support the serialization of final result trees may ignore the format attribute and the serialization attributes. Such an implementation must provide the application with some means of access to the (un-serialized) result tree, using its URI to identify it.

Implementations may provide additional mechanisms, outside the scope of this specification, for defining the way in which final result trees are processed. Such mechanisms may make use of the XSLT-defined attributes on the xsl:result-document and/or xsl:output elements, or they may use additional elements or attributes in an implementation-defined namespace.

Example: Multiple Result Documents

The following example takes an XHTML document as input, and breaks it up so that the text following each <h1> element is included in a separate document. A new document toc.html is constructed to act as an index:

<xsl:stylesheet
        version="3.0"
        xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
        xmlns:xhtml="http://www.w3.org/1999/xhtml">
        
<xsl:output name="toc-format" method="xhtml" indent="yes"
     doctype-system="http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"
     doctype-public="-//W3C//DTD XHTML 1.0 Strict//EN"/>
            
<xsl:output name="section-format" method="xhtml" indent="no"
     doctype-system="http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"
     doctype-public="-//W3C//DTD XHTML 1.0 Transitional//EN"/>       
         
<xsl:template match="/">
  <xsl:result-document href="toc.html" 
                       format="toc-format" 
                       validation="strict">
    <html xmlns="http://www.w3.org/1999/xhtml">
      <head><title>Table of Contents</title></head>
      <body>
        <h1>Table of Contents</h1>
        <xsl:for-each select="/*/xhtml:body/(*[1] | xhtml:h1)">
          <p>
            <a href="section{position()}.html">
              <xsl:value-of select="."/>
            </a>
          </p>
        </xsl:for-each>
      </body>
    </html>
  </xsl:result-document>
  <xsl:for-each-group select="/*/xhtml:body/*" group-starting-with="xhtml:h1">
    <xsl:result-document href="section{position()}.html" 
                         format="section-format" validation="strip">         
      <html xmlns="http://www.w3.org/1999/xhtml">
        <head><title><xsl:value-of select="."/></title></head>
        <body>
          <xsl:copy-of select="current-group()"/>
        </body>
      </html>
    </xsl:result-document>
  </xsl:for-each-group>
</xsl:template>

</xsl:stylesheet>

There are restrictions on the use of the xsl:result-document instruction, designed to ensure that the results are fully interoperable even when processors optimize the sequence in which instructions are evaluated. Informally, the restriction is that the xsl:result-document instruction can only be used while writing a final result tree, not while writing to a temporary tree or a sequence. This restriction is defined formally as follows.

[Definition: Each instruction in the stylesheet is evaluated in one of two possible output states: final output state or temporary output state ].

[Definition: The first of the two output states is called final output state. This state applies when instructions are writing to a final result tree.]

[Definition: The second of the two output states is called temporary output state. This state applies when instructions are writing to a temporary tree or any other non-final destination.]

The instructions in the initial template are evaluated in final output state. An instruction is evaluated in the same output state as its calling instruction, except that xsl:variable, xsl:param, xsl:with-param, xsl:function, xsl:key, xsl:sort, and xsl:merge-key always evaluate the instructions in their contained sequence constructor in temporary output state.

[ERR XTDE1480] It is a dynamic error to evaluate the xsl:result-document instruction in temporary output state.

[ERR XTDE1490] It is a dynamic error for a transformation to generate two or more final result trees with the same URI.

Note:

Note, this means that it is an error to evaluate more than one xsl:result-document instruction that omits the href attribute, or to evaluate any xsl:result-document instruction that omits the href attribute if an initial final result tree is created implicitly.

In addition, an implementation may report this error if it is able to detect that two or more final result trees are generated with different URIs that refer to the same physical resource.

Technically, the result of evaluating the xsl:result-document instruction is an empty sequence. This means it does not contribute any nodes to the result of the sequence constructor it is part of.

[ERR XTDE1500] It is a dynamic error for a stylesheet to write to an external resource and read from the same resource during a single transformation, if the same absolute URI is used to access the resource in both cases.

In addition, an implementation may report this error if it is able to detect that a transformation writes to a resource and reads from the same resource using different URIs that refer to the same physical resource. Note that if the error is not detected, it is implementation-dependent whether the document that is read from the resource reflects its state before or after the result tree is written.

24.2 Validation

It is possible to control the type annotation applied to individual element and attribute nodes as they are constructed. This is done using the type and validation attributes of the xsl:element, xsl:attribute, xsl:copy, xsl:copy-of, xsl:document, and xsl:result-document instructions, or the xsl:type and xsl:validation attributes of a literal result element.

The [xsl:]type attribute is used to request validation of an element or attribute against a specific simple or complex type defined in a schema. The [xsl:]validation attribute is used to request validation against the global element or attribute declaration whose name matches the name of the element or attribute being validated.

The [xsl:]type and [xsl:]validation attributes are mutually exclusive. Both are optional, but if one is present then the other must be omitted. If both attributes are omitted, the effect is the same as specifying the validation attribute with the value specified in the [xsl:]default-validation attribute of the innermost containing element having such an attribute; if this is not specified, the effect is the same as specifying validation="strip".

The [xsl:]default-validation attribute defines the default value of the validation attribute of all xsl:element, xsl:attribute, xsl:copy, xsl:copy-of, xsl:document, and xsl:result-document instructions, and of the xsl:validation attribute of all literal result elements , appearing within its scope. It also determines the validation applied to the implicit final result tree created in the absence of an xsl:result-document instruction. This default applies within the containing stylesheet module or package: it does not extend to included or imported stylesheet modules or used packages. If the attribute is omitted, the default is strip. The permitted values are preserve and strip.

[ERR XTSE1505] It is a static error if both the [xsl:]type and [xsl:]validation attributes are present on the xsl:element, xsl:attribute, xsl:copy, xsl:copy-of, xsl:document, or xsl:result-document instructions, or on a literal result element.

The detailed rules for validation vary depending on the kind of node being validated. The rules for element and attribute nodes are given in 24.2.1 Validating Constructed Elements and Attributes, while those for document nodes are given in 24.2.2 Validating Document Nodes.

24.2.1 Validating Constructed Elements and Attributes

24.2.1.1 Validation using the [xsl:]validation Attribute

The [xsl:]validation attribute defines the validation action to be taken. It determines not only the type annotation of the node that is constructed by the relevant instruction itself, but also the type annotations of all element and attribute nodes that have the constructed node as an ancestor. Conceptually, the validation requested for a child element or attribute node is applied before the validation requested for its parent element. For example, if the instruction that constructs a child element specifies validation="strict", this will cause the child element to be checked against an element declaration, but if the instruction that constructs its parent element specifies validation="strip", then the final effect will be that the child node is annotated as xs:untyped.

In the paragraphs below, the term contained nodes means the elements and attributes that have the newly constructed node as an ancestor.

  • The value strip indicates that the new node and each of the contained nodes will have the type annotation xs:untyped if it is an element, or xs:untypedAtomic if it is an attribute. Any previous type annotation present on a contained element or attribute node (for example, a type annotation that is present on an element copied from a source document) is also replaced by xs:untyped or xs:untypedAtomic as appropriate. The typed value of the node is changed to be the same as its string value, as an instance of xs:untypedAtomic. In the case of elements the nilled property is set to false. The values of the is-id and is-idrefs properties are unchanged. Schema validation is not invoked.

  • The value preserve indicates that nodes that are copied will retain their type annotations, but nodes whose content is newly constructed will be annotated as xs:anyType in the case of elements, or xs:untypedAtomic in the case of attributes. Schema validation is not invoked. The detailed effect depends on the instruction:

    • In the case of xsl:element and literal result elements, the new element has a type annotation of xs:anyType, and the type annotations of contained nodes are retained unchanged.

    • In the case of xsl:attribute, the effect is exactly the same as specifying validation="strip": that is, the new attribute will have the type annotation xs:untypedAtomic.

    • In the case of xsl:copy-of, all the nodes that are copied will retain their type annotations unchanged.

    • In the case of xsl:copy, the effect depends on the kind of node being copied.

      1. Where the node being copied is an attribute, the copied attribute will retain its type annotation.

      2. Where the node being copied is an element, the copied element will have a type annotation of xs:anyType (because this instruction does not copy the content of the element, it would be wrong to assume that the type is unchanged); but any contained nodes will have their type annotations retained in the same way as with xsl:element.

  • The value strict indicates that type annotations are established by performing strict schema validity assessment on the element or attribute node created by this instruction as follows:

    • In the case of an element, a top-level element declaration is identified whose local name and namespace (if any) match the name of the element, and schema-validity assessment is carried out according to the rules defined in [XML Schema Part 1] (section 3.3.4 "Element Declaration Validation Rules", validation rule "Schema-Validity Assessment (Element)", clauses 1.1 and 2, using the top-level element declaration as the "declaration stipulated by the processor", which is mentioned in clause 1.1.1.1). The element is considered valid if the result of the schema validity assessment is a PSVI in which the relevant element node has a validity property whose value is valid. If there is no matching element declaration, or if the element is not considered valid, the transformation fails [see ERR XTTE1510], [see ERR XTTE1512]. In effect this means that the element being validated must be declared using a top-level declaration in the schema, and must conform to its declaration. The process of validation applies recursively to contained elements and attributes to the extent required by the schema definition.

      Note:

      It is not an error if the identified type definition is a simple type, although [XML Schema Part 1] does not define explicitly that this case is permitted.

    • In the case of an attribute, a top-level attribute declaration is identified whose local name and namespace (if any) match the name of the attribute, and schema-validity assessment is carried out according to the rules defined in [XML Schema Part 1] (section 3.2.4 "Attribute Declaration Validation Rules", validation rule "Schema-Validity Assessment (Attribute)"). The attribute is considered valid if the result of the schema validity assessment is a PSVI in which the relevant attribute node has a validity property whose value is valid. If the attribute is not considered valid, the transformation fails [see ERR XTTE1510]. In effect this means that the attribute being validated must be declared using a top-level declaration in the schema, and must conform to its declaration.

    • The schema components used to validate an element or attribute may be located in any way described by [XML Schema Part 1] (see section 4.3.2, How schema documents are located on the Web). The components in the schema constructed from the synthetic schema document (see 3.16 Importing Schema Components) will always be available for validating constructed nodes; if additional schema components are needed, they may be located in other ways, for example implicitly from knowledge of the namespace in which the elements and attributes appear, or using the xsi:schemaLocation attribute of elements within the tree being validated.

    • If no validation is performed for a node, which can happen when the schema specifies lax or skip validation for that node or for a subtree, then the node is annotated as xs:anyType in the case of an element, and xs:untypedAtomic in the case of an attribute.

  • The value lax has the same effect as the value strict, except that whereas strict validation fails if there is no matching top-level element declaration or if the outcome of validity assessment is a validity property of invalid or notKnown, lax validation fails only if the outcome of validity assessment is a validity property of invalid. That is, lax validation does not cause a type error when the outcome is notKnown.

    In practice this means that the element or attribute being validated must conform to its declaration if a top-level declaration is available. If no such declaration is available, then the element or attribute is not validated, but its attributes and children are validated, again with lax validation. Any nodes whose validation outcome is a validity property of notKnown are annotated as xs:anyType in the case of an element, and xs:untypedAtomic in the case of an attribute.

    Note:

    When the parent element lacks a declaration, the XML Schema specification defines the recursive checking of children and attributes as optional. For this specification, this recursive checking is required.

    Note:

    If an element that is being validated has an xsi:type attribute, then the value of the xsi:type attribute will be taken into account when performing the validation. However, the presence of an xsi:type attribute will not of itself cause an element to be validated: if validation against a named type is required, as distinct from validation against a top-level element declaration, then it must be requested using the XSLT [xsl:]type attribute on the instruction that invokes the validation, as described in section 24.2.1.2 Validation using the [xsl:]type Attribute

[ERR XTTE1510] If the validation attribute of an xsl:element, xsl:attribute, xsl:copy, xsl:copy-of, or xsl:result-document instruction, or the xsl:validation attribute of a literal result element, has the effective value strict, and schema validity assessment concludes that the validity of the element or attribute is invalid or unknown, a type error occurs. As with other type errors, the error may be signaled statically if it can be detected statically.

[ERR XTTE1512] If the validation attribute of an xsl:element, xsl:attribute, xsl:copy, xsl:copy-of, or xsl:result-document instruction, or the xsl:validation attribute of a literal result element, has the effective value strict, and there is no matching top-level declaration in the schema, then a type error occurs. As with other type errors, the error may be signaled statically if it can be detected statically.

[ERR XTTE1515] If the validation attribute of an xsl:element, xsl:attribute, xsl:copy, xsl:copy-of, or xsl:result-document instruction, or the xsl:validation attribute of a literal result element, has the effective value lax, and schema validity assessment concludes that the element or attribute is invalid, a type error occurs. As with other type errors, the error may be signaled statically if it can be detected statically.

Note:

No mechanism is provided to validate an element or attribute against a local declaration in a schema. Such validation can usually be achieved by applying validation to a containing element for which a top-level element declaration exists.

24.2.1.2 Validation using the [xsl:]type Attribute

The [xsl:]type attribute takes as its value a QName. This must be the name of a type definition included in the in-scope schema components for the stylesheet. If the QName has no prefix, it is expanded using the default namespace established using the effective [xsl:]xpath-default-namespace attribute if there is one; otherwise, it is taken as being a name in no namespace.

If the [xsl:]type attribute is present, then the newly constructed element or attribute is validated against the type definition identified by this attribute.

  • In the case of an element, schema-validity assessment is carried out according to the rules defined in [XML Schema Part 1] (section 3.3.4 "Element Declaration Validation Rules", validation rule "Schema-Validity Assessment (Element)", clauses 1.2 and 2), using this type definition as the "processor-stipulated type definition". The element is considered valid if the result of the schema validity assessment is a PSVI in which the relevant element node has a validity property whose value is valid.

  • In the case of an attribute, the attribute is considered valid if (in the terminology of XML Schema) the attribute's normalized value is locally valid with respect to that type definition according to the rules for "String Valid" ([XML Schema Part 1], section 3.14.4). (Normalization here refers to the process of normalizing whitespace according to the rules of the whiteSpace facet for the datatype).

  • If the element or attribute is not considered valid, as defined above, the transformation fails [see ERR XTTE1540].

If an element node is validated against the type xs:untyped, the effect is the same as specifying validation="strip": that is, the elements and attributes in the subtree rooted at the target element are copied with a type annotation of xs:untyped or xs:untypedAtomic respectively.

If an element or attribute node is validated against the type xs:untypedAtomic, the effect is the same as specifying [xsl:]type="xs:string" except that when validation succeeds, the returned element or attribute has a type annotation of xs:untypedAtomic. Validation fails in the case of an element with element children.

[ERR XTSE1520] It is a static error if the value of the type attribute of an xsl:element, xsl:attribute, xsl:copy, xsl:copy-of, xsl:document, or xsl:result-document instruction, or the xsl:type attribute of a literal result element, is not a valid QName, or if it uses a prefix that is not defined in an in-scope namespace declaration, or if the QName is not the name of a type definition included in the in-scope schema components for the stylesheet.

[ERR XTSE1530] It is a static error if the value of the type attribute of an xsl:attribute instruction refers to a complex type definition.

[ERR XTTE1535] It is a type error if the value of the type attribute of an xsl:copy or xsl:copy-of instruction refers to a complex type definition and one or more of the items being copied is an attribute node.

[ERR XTTE1540] It is a type error if an [xsl:]type attribute is defined for a constructed element or attribute, and the outcome of schema validity assessment against that type is that the validity property of that element or attribute information item is other than valid.

Note:

Like other type errors, this error may be signaled statically if it can be detected statically. For example, the instruction <xsl:attribute name="dob" type="xs:date">1999-02-29</xsl:attribute> may result in a static error being signaled. If the error is not signaled statically, it will be signaled when the instruction is evaluated.

24.2.1.3 The Validation Process

As well as checking for validity against the schema, the validity assessment process causes type annotations to be associated with element and attribute nodes. If default values for elements or attributes are defined in the schema, the validation process will where necessary create new nodes containing these default values.

Validation of an element or attribute node only takes into account constraints on the content of the element or attribute. Validation rules affecting the document as a whole are not applied. Specifically, this means:

  • The validation rule "Validation Root Valid (ID/IDREF)" is not applied. This means that validation will not fail if there are non-unique ID values or dangling IDREF values in the subtree being validated.

  • The validation rule "Validation Rule: Identity-constraint Satisfied" should be applied.

  • There is no check that the document contains unparsed entities whose names match the values of nodes of type xs:ENTITY or xs:ENTITIES. (XSLT 3.0 provides no facility to construct unparsed entities within a tree.)

  • There is no check that the document contains notations whose names match the values of nodes of type xs:NOTATION. (The XDM data model makes no provision for notations to be represented in the tree.)

With these caveats, validating a newly constructed element, using strict or lax validation, is equivalent to the following steps:

  1. The element is serialized to textual XML form, according to the rules defined in [XSLT and XQuery Serialization] using the XML output method, with all parameters defaulted. Note that this process discards any existing type annotations.

  2. The resulting XML document is parsed to create an XML Information Set (see [XML Information Set].)

  3. The Information Set produced in the previous step is validated according to the rules in [XML Schema Part 1]. The result of this step is a Post-Schema Validation Infoset (PSVI). If the validation process is not successful (as defined above), a type error is raised.

  4. The PSVI produced in the previous step is converted back into the XDM data model by the mapping described in [Data Model] (Section 3.3.1 Mapping PSVI Additions to Node Properties DM30). This process creates nodes with simple or complex type annotations based on the types established during schema validation.

Validating an attribute using strict or lax validation requires a modified version of this procedure. A copy of the attribute is first added to an element node that is created for the purpose, and namespace fixup (see 5.8.3 Namespace Fixup) is performed on this element node. The name of this element is of no consequence, but it must be the same as the name of a synthesized element declaration of the form:

<xs:element name="E">
  <xs:complexType>
    <xs:sequence/>
    <xs:attribute ref="A"/>
  </xs:complexType>
</xs:element>

where A is the name of the attribute being validated.

This synthetic element is then validated using the procedure given above for validating elements, and if it is found to be valid, a copy of the validated attribute is made, retaining its type annotation, but detaching it from the containing element (and thus, from any namespace nodes).

The XDM data model does not permit an attribute node with no parent to have a typed value that includes a namespace-qualified name, that is, a value whose type is derived from xs:QName or xs:NOTATION. This restriction is imposed because these types rely on the namespace nodes of a containing element to resolve namespace prefixes. Therefore, it is an error to validate a parentless attribute against such a type. This affects the instructions xsl:attribute, xsl:copy, and xsl:copy-of.

[ERR XTTE1545] A type error occurs if a type or validation attribute is defined (explicitly or implicitly) for an instruction that constructs a new attribute node, if the effect of this is to cause the attribute value to be validated against a type that is derived from, or constructed by list or union from, the primitive types xs:QName or xs:NOTATION.

24.2.2 Validating Document Nodes

It is possible to apply validation to a document node. This happens when a new document node is constructed by one of the instructions xsl:stream, xsl:document, xsl:result-document, xsl:copy, or xsl:copy-of, and this instruction has a type attribute, or a validation attribute with the value strict or lax.

Document-level validation is not applied to the document node that is created implicitly when a variable-binding element has no select attribute and no as attribute (see 9.4 Creating Implicit Document Nodes). This is equivalent to using validation="preserve" on xsl:document: nodes within such trees retain their type annotation. Similarly, validation is not applied to document nodes created using xsl:message or xsl:assert.

The values validation="preserve" and validation="strip" do not request validation. In the first case, all element and attribute nodes within the tree rooted at the new document node retain their type annotations. In the second case, elements within the tree have their type annotation set to xs:untyped, while attributes have their type annotation set to xs:untypedAtomic.

When validation is requested for a document node (that is, when validation is set to strict or lax, or when a type attribute is present), the following processing takes place:

  • [ERR XTTE1550] A type error occurs unless the children of the document node comprise exactly one element node, no text nodes, and zero or more comment and processing instruction nodes, in any order.

  • The single element node child is validated, using the supplied values of the validation and type attributes, as described in 24.2.1 Validating Constructed Elements and Attributes.

    Note:

    The type attribute on xsl:stream, xsl:document and xsl:result-document, and on xsl:copy and xsl:copy-of when copying a document node, thus refers to the required type of the element node that is the only element child of the document node. It does not refer to the type of the document node itself.

  • The validation rule "Validation Root Valid (ID/IDREF)" is applied to the single element node child of the document node. This means that validation will fail if there are non-unique ID values or dangling IDREF values in the document tree.

  • Identity constraints, as defined in section 3.11 of [XML Schema Part 1], are checked. (This refers to constraints defined using xs:unique, xs:key, and xs:keyref.)

  • There is no check that the tree contains unparsed entities whose names match the values of nodes of type xs:ENTITY or xs:ENTITIES. This is because there is no facility in XSLT 3.0 to create unparsed entities in a result tree. It is possible to add unparsed entity declarations to the result document by referencing a suitable DOCTYPE during serialization.

  • There is no check that the document contains notations whose names match the values of nodes of type xs:NOTATION. This is because notations are not part of the XDM data model. It is possible to add notations to the result document by referencing a suitable DOCTYPE during serialization.

  • All other children of the document node (comments and processing instructions) are copied unchanged.

[ERR XTTE1555] It is a type error if, when validating a document node, document-level constraints (such as ID/IDREF constraints) are not satisfied.

25 Serialization

A processor may output a final result tree as a sequence of octets, although it is not required to be able to do so (see 26 Conformance). Stylesheet authors can use xsl:output declarations to specify how they wish result trees to be serialized. If a processor serializes a final result tree, it must do so as specified by these declarations.

The rules governing the output of the serializer are defined in [XSLT and XQuery Serialization]. The serialization is controlled using a number of serialization parameters. The values of these serialization parameters may be set within the stylesheet, using the xsl:output, xsl:result-document, and xsl:character-map declarations.

<!-- Category: declaration -->
<xsl:output
  name? = eqname
  method? = "xml" | "html" | "xhtml" | "text" | eqname
  byte-order-mark? = "yes" | "no"
  cdata-section-elements? = eqnames
  doctype-public? = string
  doctype-system? = string
  encoding? = string
  escape-uri-attributes? = "yes" | "no"
  html-version? = decimal
  include-content-type? = "yes" | "no"
  indent? = "yes" | "no"
  item-separator? = string
  media-type? = string
  normalization-form? = "NFC" | "NFD" | "NFKC" | "NFKD" | "fully-normalized" | "none" | nmtoken
  omit-xml-declaration? = "yes" | "no"
  parameter-document? = uri
  standalone? = "yes" | "no" | "omit"
  suppress-indentation? = eqnames
  undeclare-prefixes? = "yes" | "no"
  use-character-maps? = eqnames
  version? = nmtoken />

The xsl:output declaration is optional; if used, it must always appear as a top-level element within a stylesheet module.

A stylesheet may contain multiple xsl:output declarations and may include or import stylesheet modules that also contain xsl:output declarations. The name of an xsl:output declaration is the value of its name attribute, if any.

[Definition: All the xsl:output declarations within a package that share the same name are grouped into a named output definition; those that have no name are grouped into a single unnamed output definition.]

An output definition is scoped to a package. If this is a library package the output definition applies only to xsl:result-document instructions within the same package. If it is the top-level package, the output definition applies to xsl:result-document instructions within the same package and also to the implicit final result tree.

A stylesheet always includes an unnamed output definition; in the absence of an unnamed xsl:output declaration, the unnamed output definition is equivalent to the one that would be used if the stylesheet contained an xsl:output declaration having no attributes.

A named output definition is used when its name matches the format attribute used in an xsl:result-document element. The unnamed output definition is used when an xsl:result-document element omits the format attribute. It is also used when serializing the final result tree that is created implicitly in the absence of an xsl:result-document element.

All the xsl:output elements making up an output definition are effectively merged. For those attributes whose values are namespace-sensitive, the merging is done after lexical QNames have been converted into expanded QNames. For the cdata-section-elements and suppress-indentation attributes, the output definition uses the union of the values from all the constituent xsl:output declarations. For the use-character-maps attribute, the output definition uses the concatenation of the sequences of expanded QNames values from all the constituent xsl:output declarations, taking them in order of increasing import precedence, or where several have the same import precedence, in declaration order. For other attributes, the output definition uses the value of that attribute from the xsl:output declaration with the highest import precedence.

The parameter-document attribute allows serialization parameters to be supplied in an external document. The external document must contain an output:serialization-parameters element with the format described in Section 3.1 Setting Serialization Parameters by Means of a Data Model Instance SER30, and the parameters are interpreted as described in that specification.

If present, the URI supplied in the parameter-document attribute is dereferenced, after resolution against the base URI of the xsl:output element if it is a relative reference. If the location of the stylesheet at development time is different from the deployed location, any relative reference should be resolved against the deployed location. A serialization error occurs if the result of dereferencing the URI is ill-formed or invalid; but if no document can be found at the specified location, the attribute may be ignored.

A serialization parameter specified in the parameter-document takes precedence over a value supplied directly in the output declaration, except that the values of the cdata-section-elements and suppress-indentation attributes are merged in the same way as when multiple xsl:output declarations are merged.

[ERR XTSE1560] It is a static error if two xsl:output declarations within an output definition specify explicit values for the same attribute (other than cdata-section-elements and use-character-maps), with the values of the attributes being not equal, unless there is another xsl:output declaration within the same output definition that has higher import precedence and that specifies an explicit value for the same attribute.

If none of the xsl:output declarations within an output definition specifies a value for a particular attribute, then the corresponding serialization parameter takes a default value. The default value depends on the chosen output method.

There are some serialization parameters that apply to some output methods but not to others. For example, the indent attribute has no effect on the text output method. If a value is supplied for an attribute that is inapplicable to the output method, its value is not passed to the serializer. The processor may validate the value of such an attribute, but is not required to do so.

An implementation may allow the attributes of the xsl:output declaration to be overridden, or the default values to be changed, using the API that controls the transformation.

The location to which final result trees are serialized (whether in filestore or elsewhere) is implementation-defined (which in practice may mean that it is controlled using an implementation-defined API). However, these locations must satisfy the constraint that when two final result trees are both created (implicitly or explicitly) using relative URI references in the href attribute of the xsl:result-document instruction, then these relative URI references may be used to construct references from one tree to the other, and such references must remain valid when both result trees are serialized.

The method attribute on the xsl:output element identifies the overall method that is to be used for outputting the final result tree.

[ERR XTSE1570] The value must (if present) be a valid EQName. If it is a lexical QName with no a prefix, then it identifies a method specified in [XSLT and XQuery Serialization] and must be one of xml, html, xhtml, or text. If it is a lexical QName with a prefix, then the lexical QName is expanded into an expanded QName as described in 5.1 Qualified Names; the expanded QName identifies the output method; the behavior in this case is not specified by this document.

The default for the method attribute depends on the contents of the tree being serialized, and is chosen as follows. If the document node of the final result tree has an element child, and any text nodes preceding the first element child of the document node of the result tree contain only whitespace characters, then:

In all other cases, the default output method is xml.

The default output method is used if the selected output definition does not include a method attribute.

The other attributes on xsl:output provide parameters for the output method. The following attributes are allowed:

The item-separator serialization parameter defined in [XSLT and XQuery Serialization] is not available in xsl:output; it is not applicable, because the sequence that is serialized by XSLT is always a singleton document node. Formally therefore, the serializer is always invoked passing an empty string as the value of this parameter.

If the processor performs serialization, then it must signal any serialization errors that occur. These have the same effect as dynamic errors: that is, the processor must signal the error and must not finish as if the transformation had been successful.

25.1 Character Maps

[Definition: A character map allows a specific character appearing in a text or attribute node in the final result tree to be substituted by a specified string of characters during serialization.] The effect of character maps is defined in [XSLT and XQuery Serialization].

The character map that is supplied as a parameter to the serializer is determined from the xsl:character-map elements referenced from the xsl:output declaration for the selected output definition.

The xsl:character-map element is a declaration that may appear as a child of the xsl:stylesheet element.

<!-- Category: declaration -->
<xsl:character-map
  name = eqname
  use-character-maps? = eqnames >
  <!-- Content: (xsl:output-character*) -->
</xsl:character-map>

The xsl:character-map declaration declares a character map with a name and a set of character mappings. The character mappings are specified by means of xsl:output-character elements contained either directly within the xsl:character-map element, or in further character maps referenced in the use-character-maps attribute.

The required name attribute provides a name for the character map. When a character map is used by an output definition or another character map, the character map with the highest import precedence is used.

The name of a character map is local to the package in which its declaration appears; it may be referenced only from within the same package.

[ERR XTSE1580] It is a static error if the stylesheet contains two or more character maps with the same name and the same import precedence, unless it also contains another character map with the same name and higher import precedence.

The optional use-character-maps attribute lists the names of further character maps that are included into this character map.

[ERR XTSE1590] It is a static error if a name in the use-character-maps attribute of the xsl:output or xsl:character-map elements does not match the name attribute of any xsl:character-map in the stylesheet.

[ERR XTSE1600] It is a static error if a character map references itself, directly or indirectly, via a name in the use-character-maps attribute.

It is not an error if the same character map is referenced more than once, directly or indirectly.

An output definition, after recursive expansion of character maps referenced via its use-character-maps attribute, may contain several mappings for the same character. In this situation, the last character mapping takes precedence. To establish the ordering, the following rules are used:

  • Within a single xsl:character-map element, the characters defined in character maps referenced in the use-character-maps attribute are considered before the characters defined in the child xsl:output-character elements.

  • The character maps referenced in a single use-character-maps attribute are considered in the order in which they are listed in that attribute. The expansion is depth-first: each referenced character map is fully expanded before the next one is considered.

  • Two xsl:output-character elements appearing as children of the same xsl:character-map element are considered in document order.

The xsl:output-character element is defined as follows:

<xsl:output-character
  character = char
  string = string />

The character map that is passed as a parameter to the serializer contains a mapping for the character specified in the character attribute to the string specified in the string attribute.

Character mapping is not applied to characters for which output escaping has been disabled as described in 25.2 Disabling Output Escaping.

If a character is mapped, then it is not subjected to XML or HTML escaping.

Example: Using Character Maps to Generate Non-XML Output

Character maps can be useful when producing serialized output in a format that resembles, but is not strictly conformant to, HTML or XML. For example, when the output is a JSP page, there might be a need to generate the output:

<jsp:setProperty name="user" property="id" value='<%= "id" + idValue %>'/>

Although this output is not well-formed XML or HTML, it is valid in Java Server Pages. This can be achieved by allocating three Unicode characters (which are not needed for any other purpose) to represent the strings <%, %>, and ", for example:

<xsl:character-map name="jsp">
  <xsl:output-character character="«" string="&lt;%"/>   
  <xsl:output-character character="»" string="%&gt;"/>
  <xsl:output-character character="§" string='"'/>
</xsl:character-map>

When this character map is referenced in the xsl:output declaration, the required output can be produced by writing the following in the stylesheet:

<jsp:setProperty name="user" property="id" value='«= §id§ + idValue »'/>

This works on the assumption that when an apostrophe or quotation mark is generated as part of an attribute value by the use of character maps, the serializer will (where possible) use the other choice of delimiter around the attribute value.

 

Example: Constructing a Composite Character Map

The following example illustrates a composite character map constructed in a modular fashion:

<xsl:output name="htmlDoc" use-character-maps="htmlDoc" />

<xsl:character-map name="htmlDoc"
  use-character-maps="html-chars doc-entities windows-format" />
  
<xsl:character-map name="html-chars"
  use-character-maps="latin1 ..." />

<xsl:character-map name="latin1">
  <xsl:output-character character="&#160;" string="&amp;nbsp;" />
  <xsl:output-character character="&#161;" string="&amp;iexcl;" />
  ...
</xsl:character-map>

<xsl:character-map name="doc-entities">
  <xsl:output-character character="&#xE400;" string="&amp;t-and-c;" />
  <xsl:output-character character="&#xE401;" string="&amp;chap1;" />
  <xsl:output-character character="&#xE402;" string="&amp;chap2;" />
  ...
</xsl:character-map>

<xsl:character-map name="windows-format">
  <!-- newlines as CRLF -->
  <xsl:output-character character="&#xA;" string="&#xD;&#xA;" />

  <!-- tabs as three spaces -->
  <xsl:output-character character="&#x9;" string="   " />

  <!-- images for special characters -->
  <xsl:output-character character="&#xF001;"
    string="&lt;img src='special1.gif' /&gt;" />
  <xsl:output-character character="&#xF002;"
    string="&lt;img src='special2.gif' /&gt;" />
  ...
</xsl:character-map>

Note:

When character maps are used, there is no guarantee that the serialized output will be well-formed XML (or HTML). Furthermore, the fact that the result tree was validated against a schema gives no guarantee that the serialized output will still be valid against the same schema. Conversely, it is possible to use character maps to produce schema-valid output from a result tree that would fail validation.

25.2 Disabling Output Escaping

Normally, when using the XML, HTML, or XHTML output method, the serializer will escape special characters such as & and < when outputting text nodes. This ensures that the output is well-formed. However, it is sometimes convenient to be able to produce output that is almost, but not quite well-formed XML; for example, the output may include ill-formed sections which are intended to be transformed into well-formed XML by a subsequent non-XML-aware process. For this reason, XSLT defines a mechanism for disabling output escaping.

This feature is deprecated.

This is an optional feature: it is not required that a XSLT processor that implements the serialization option should offer the ability to disable output escaping, and there is no conformance level that requires this feature.

This feature requires an extension to the serializer described in [XSLT and XQuery Serialization]. Conceptually, the final result tree provides an additional boolean property disable-escaping associated with every character in a text node. When this property is set, the normal action of the serializer to escape special characters such as & and < is suppressed.

An xsl:value-of or xsl:text element may have a disable-output-escaping attribute; the allowed values are yes or no. The default is no; if the value is yes, then every character in the text node generated by evaluating the xsl:value-of or xsl:text element should have the disable-escaping property set.

Example: Disable Output Escaping

For example,

<xsl:text disable-output-escaping="yes">&lt;</xsl:text>

should generate the single character <.

If output escaping is disabled for an xsl:value-of or xsl:text instruction evaluated when temporary output state is in effect, the request to disable output escaping is ignored.

Similarly, if an xsl:value-of or xsl:text instruction specifies that output escaping is to be disabled when writing to a final result tree that is not being serialized, the request to disable output escaping is ignored.

If output escaping is disabled for text within an element that would normally be output using a CDATA section, because the element is listed in the cdata-section-elements, then the relevant text will not be included in a CDATA section. In effect, CDATA is treated as an alternative escaping mechanism, which is disabled by the disable-output-escaping option.

Example: Interaction of Output Escaping and CDATA

For example, if <xsl:output cdata-section-elements="title"/> is specified, then the following instructions:

<title>
  <xsl:text disable-output-escaping="yes">This is not &lt;hr/&gt; 
                                          good coding practice</xsl:text>
</title>

should generate the output:

<title><![CDATA[This is not ]]><hr/><![CDATA[ good coding practice]]></title>

The disable-output-escaping attribute may be used with the html output method as well as with the xml output method. The text output method ignores the disable-output-escaping attribute, since this method does not perform any output escaping.

A processor will only be able to disable output escaping if it controls how the final result tree is output. This might not always be the case. For example, the result tree might be used as a source tree for another XSLT transformation instead of being output. It is implementation-defined whether (and under what circumstances) disabling output escaping is supported. If disabling output escaping is not supported, any request to disable output escaping is ignored.

If output escaping is disabled for a character that is not representable in the encoding that the processor is using for output, the request to disable output escaping is ignored in respect of that character.

Since disabling output escaping might not work with all implementations and can result in XML that is not well-formed, it should be used only when there is no alternative.

Note:

When disable-output-escaping is used, there is no guarantee that the serialized output will be well-formed XML (or HTML). Furthermore, the fact that the result tree was validated against a schema gives no guarantee that the serialized output will still be valid against the same schema. Conversely, it is possible to use disable-output-escaping to produce schema-valid output from a result tree that would fail validation.

Note:

The facility to define character maps for use during serialization, as described in 25.1 Character Maps, has been produced as an alternative mechanism that can be used in many situations where disabling of output escaping was previously necessary, without the same difficulties.

26 Conformance

A processor that claims conformance with this specification must satisfy the conformance requirements for a basic XSLT processor and for each of the optional features with which it claims conformance.

The following optional features are defined:

  1. The schema-awareness feature, defined in 26.2 Schema-Awareness Conformance Feature

  2. The serialization feature, defined in 26.3 Serialization Feature

  3. The backwards compatibility feature, defined in 26.4 Compatibility Features

  4. The streaming feature, defined in 26.5 Streaming Feature.

  5. The dynamic evaluation feature, defined in 26.6 Dynamic Evaluation Feature.

  6. The XQuery invocation feature, defined in 26.7 XQuery Invocation Feature.

A processor that does not claim conformance with an optional feature must satisfy the requirements for processors that do not implement that feature.

Note:

There is no conformance level or feature defined in this specification that requires implementation of the static typing features described in [XPath 3.0]. An XSLT processor may provide a user option to invoke static typing, but to be conformant with this specification it must allow a stylesheet to be processed with static typing disabled. The interaction of XSLT stylesheets with the static typing feature of XPath 3.0 has not been specified, so the results of using static typing, if available, are implementation-defined.

An XSLT processor takes as its inputs a stylesheet and zero or more XDM trees conforming to the data model defined in [Data Model]. It is not required that the processor supports any particular method of constructing XDM trees, but conformance can only be tested if it provides a mechanism that enables XDM trees representing the stylesheet and primary source document to be constructed and supplied as input to the processor.

The output of the XSLT processor consists of zero or more final result trees. It is not required that the processor supports any particular method of accessing a final result tree, but if it does not support the serialization feature, conformance can only be tested if it provides some alternative mechanism that enables access to the results of the transformation.

Certain facilities in this specification are described as producing implementation-defined results. A claim that asserts conformance with this specification must be accompanied by documentation stating the effect of each implementation-defined feature. For convenience, a non-normative checklist of implementation-defined features is provided at F Checklist of Implementation-Defined Features.

A conforming processor must signal any static error occurring in the stylesheet, or in any XPath expression, except where specified otherwise either for individual error conditions or under the general provisions for forwards compatible behavior (see 3.11 Forwards Compatible Processing). After signaling such an error, the processor may continue for the purpose of signaling additional errors, but must terminate abnormally without performing any transformation.

When a dynamic error occurs during the course of a transformation, and is not caught using xsl:catch, the processor must signal it and must eventually terminate abnormally. If a recoverable error occurs, the processor must either signal it and terminate abnormally, or it must take the defined recovery action and continue processing.

Some errors, notably type errors, may be treated as static errors or dynamic errors at the discretion of the processor.

A conforming processor may impose limits on the processing resources consumed by the processing of a stylesheet.

26.1 Basic XSLT Processor

[Definition: A basic XSLT processor is an XSLT processor that implements all the mandatory requirements of this specification with the exception of constructs explicitly associated with an optional feature.] These constructs are listed below.

The mandatory requirements of this specification are taken to include the mandatory requirements of XPath 3.0, as described in [XPath 3.0]. A requirement is mandatory unless the specification includes wording (such as the use of the words should or may) that clearly indicates that it is optional.

26.2 Schema-Awareness Conformance Feature

A conformant processor must either be a conformant schema-aware XSLT processor or a conformant non-schema-aware processor.

[Definition: A schema-aware XSLT processor is an XSLT processor that implements the mandatory requirements of this specification connected with the xsl:import-schema declaration, the [xsl:]validation and [xsl:]type attributes, and the ability to handle input documents whose nodes have type annotations other than xs:untyped and xs:untypedAtomic. The mandatory requirements of this specification are taken to include the mandatory requirements of XPath 3.0, as described in [XPath 3.0]. A requirement is mandatory unless the specification includes wording (such as the use of the words should or may) that clearly indicates that it is optional.]

[Definition: A non-schema-aware processor is a processor that does not claim conformance with the schema-aware conformance feature. Such a processor must handle constructs associated with schema-aware processing as described in this section.]

[ERR XTSE1650] A non-schema-aware processor must signal a static error if the stylesheet includes an xsl:import-schema declaration.

Note:

A processor that rejects an xsl:import-schema declaration will also reject any reference to a user-defined type defined in a schema, or to a user-defined element or attribute declaration; it will not, however, reject references to the built-in types listed in 3.15 Built-in Types.

A non-schema-aware processor is not able to validate input documents, and is not able to handle input documents containing type annotations other than xs:untyped or xs:untypedAtomic. Therefore, such a processor must treat any [xsl:]validation attribute with a value of preserve or lax, or a [xsl:]default-validation attribute with a value of preserve as if the value were strip.

Note:

The values lax and preserve indicate that the validation to be applied depends on the calling application, so it is appropriate for the request to be treated differently by different kinds of processor. By contrast, requesting strict validation, either through the [xsl:]validation attribute or the type attribute, indicates that the stylesheet is expecting to deal with typed data, and therefore cannot be processed without performing the validation.

[ERR XTSE1660] A non-schema-aware processor must signal a static error if the stylesheet includes an [xsl:]type attribute, or an [xsl:]validation or [xsl:]default-validation attribute with a value other than strip, preserve, or lax.

A non-schema-aware processor constrains the data model as follows:

  • Atomic values must belong to one of the atomic types listed in 3.15 Built-in Types (except as noted below).

    An atomic value may also belong to an implementation-defined type that has been added to the context for use with extension functions or extension instructions.

    The set of constructor functions available are limited to those that construct values of the above atomic types.

    The static context, which defines the full set of type names recognized by an XSLT processor and also by the XPath processor, includes these atomic types, plus xs:anyType, xs:anySimpleType, xs:untyped, and xs:anyAtomicType.

  • Element nodes must be annotated with the type annotation xs:untyped, and attribute nodes with the type annotation xs:untypedAtomic.

[ERR XTDE1665] A non-schema-aware processor must raise a dynamic error if the input to the processor includes a node with a type annotation other than xs:untyped or xs:untypedAtomic, or an atomic value of a type other than those which a basic XSLT processor supports. This error will not arise if the input-type-annotations attribute is set to strip.

Note:

Although this is expressed in terms of a requirement to detect invalid input, an alternative approach is for a non-schema-aware processor to prevent this error condition occurring, by not providing any interfaces that would allow the situation to arise. A processor might, for example, implement a mapping from the PSVI to the data model that loses all non-trivial type annotations; or it might not accept input from a PSVI at all.

The phrase input to the processor is deliberately wide: it includes the tree containing the initial context item, trees passed as stylesheet parameters, trees accessed using the document, docFO30, and collectionFO30 functions, and trees returned by extension functions and extension instructions.

26.3 Serialization Feature

[Definition: A processor that claims conformance with the serialization feature must support the conversion of a final result tree to a sequence of octets following the rules defined in 25 Serialization.] It must respect all the attributes of the xsl:output and xsl:character-map declarations, and must provide all four output methods, xml, xhtml, html, and text. Where the specification uses words such as must and required, then it must serialize the result tree in precisely the way described; in other cases it may use an alternative, equivalent representation.

A processor may claim conformance with the serialization feature whether or not it supports the setting disable-output-escaping="yes" on xsl:text, or xsl:value-of.

A processor that does not claim conformance with the serialization feature must not signal an error merely because the stylesheet contains xsl:output or xsl:character-map declarations, or serialization attributes on the xsl:result-document instruction. Such a processor may check that these declarations and attributes have valid values, but is not required to do so. Apart from optional validation, these declarations should be ignored.

26.4 Compatibility Features

[Definition: A processor that claims conformance with the XSLT 1.0 compatibility feature must support the processing of stylesheet instructions and XPath expressions with XSLT 1.0 behavior, as defined in 3.10 Backwards Compatible Processing.]

Note that a processor that does not claim conformance with the XSLT 1.0 compatibility feature must raise a dynamic error if an instruction is evaluated whose effective version is 1.0. [see ERR XTDE0160].

Note:

The reason this is a dynamic error rather than a static error is to allow stylesheets to contain conditional logic, following different paths depending on whether the XSLT processor implements XSLT 1.0, 2.0, or 3.0. The selection of which path to use can be controlled by using the system-property function to test the xsl:version system property.

A processor that claims conformance with the XSLT 1.0 compatibility feature must permit the use of the namespace axis in XPath expressions when backwards compatible behavior is enabled. In all other circumstances, support for the namespace axis is optional.

Note:

There are no incompatibilities between 3.0 and 2.0 that would justify a 2.0-compatibility mode. When a 3.0 processor encounters a stylesheet that specifies version="2.0", evaluation therefore proceeds exactly as if it specified version="3.0". However, a software product may invoke an XSLT 2.0 processor in preference to an XSLT 3.0 processor when the stylesheet specifies version="3.0", in which case any use of new 3.0 constructs will be rejected.

26.5 Streaming Feature

[Definition: A processor that claims conformance with the streaming feature must use streamed processing in cases where (a) streaming is requested (for example by using the attribute streamable="yes" on xsl:mode, or the xsl:stream instruction) and (b) the constructs in question are guaranteed-streamable according to this specification.]

A processor that does not claim conformance with the streaming feature is not required to use streamed processing and is not required to determine whether any construct is guaranteed streamable. Such a processor must, however, implement the semantics of all constructs in the language provided that enough memory is available to perform the processing without streaming.

A processor that conforms with the feature must return the value "yes" in response to the function call system-property('xsl:supports-streaming'); a processor that does not conform with the feaure must return the value "no".

Note:

The term streamed processing as used here means the ability to process arbitrarily large input documents without ever-increasing memory requirements.

26.6 Dynamic Evaluation Feature

[Definition: A processor that claims conformance with the dynamic evaluation feature must evaluate the xsl:evaluate function as described in this specification.]

A processor that does not claim conformance with the dynamic evaluation feature must report a dynamic error if an xsl:evaluate instruction is evaluated. It must not report a static error merely because of the presence of an xsl:evaluate instruction in the stylesheet, unless a processor that conforms with the feature would report the same static error.

A processor that conforms with the feature must return the value "yes" in response to the function call system-property('xsl:supports-dynamic-evaluation'); a processor that does not conform with the feaure must return the value "no".

A processor that conforms with the feature must return the value true in response to the function call element-available('xsl:evaluate'); a processor that does not conform with the feaure must return the value false.

Note:

A processor may allow dynamic evaluation to be enabled and disabled by means of configuration settings, perhaps for security reasons. In consequence, it may be impossible to tell during static analysis of the stylesheet whether or not the feature will be available during execution. A stylesheet author wanting to check whether the feature is available should therefore make the test using a run-time call on system-property, rather than relying on tests in an [xsl:]use-when attribute.

26.7 XQuery Invocation Feature

[Definition: A processor that claims conformance with the XQuery invocation feature must allow XQuery library modules to be referenced in xsl:use-package, and must allow the using package to reference the public functions and variables declared in the referenced library module.]

A References

A.1 Normative References

Data Model
XQuery and XPath Data Model (XDM) 3.0, Norman Walsh, John Snelson, Editors. World Wide Web Consortium, 22 October 2013. This version is http://www.w3.org/TR/2013/PR-xpath-datamodel-30-20131022/. The latest version is available at http://www.w3.org/TR/xpath-datamodel-30/.
Functions and Operators
XQuery and XPath Functions and Operators 3.0, Michael Kay, Editor. World Wide Web Consortium, 22 October 2013. This version is http://www.w3.org/TR/2013/PR-xpath-functions-30-20131022/. The latest version is available at http://www.w3.org/TR/xpath-functions-30/.
XML Information Set
XML Information Set (Second Edition), Richard Tobin and John Cowan, Editors. World Wide Web Consortium, 04 Feb 2004. This version is http://www.w3.org/TR/2004/REC-xml-infoset-20040204. The latest version is available at http://www.w3.org/TR/xml-infoset.
ISO 15924
ISO (International Organization for Standardization) Information and documentation — Codes for the representation of names of scripts ISO 15924:2004, January 2004.
ISO 15924 Register
Unicode Consortium. Codes for the representation of names of scripts — Alphabetical list of four-letter script codes. See http://www.unicode.org/iso15924/iso15924-codes.html. Retrieved February 2013; continually updated.
XSLT and XQuery Serialization
XSLT and XQuery Serialization 3.0, Henry Zongaro, Editor. World Wide Web Consortium, 22 October 2013. This version is http://www.w3.org/TR/2013/PR-xslt-xquery-serialization-30-20131022/. The latest version is available at http://www.w3.org/TR/xslt-xquery-serialization-30/.
RFC 4627
IETF. The application/json Media Type for JavaScript Object Notation (JSON). July 2006. See http://www.ietf.org/rfc/rfc4627.txt
ECMA-404
ECMA International. The JSON Data Interchange Format October 2013. See http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-404.pdf.
UNICODE
Unicode Consortium. The Unicode Standard as updated from time to time by the publication of new versions. See http://www.unicode.org/standard/versions/ for the latest version and additional information on versions of the standard and of the Unicode Character Database. The version of Unicode to be used is implementation-defined, but implementations are recommended to use the latest Unicode version.
UNICODE TR10
Unicode Consortium. Unicode Technical Standard #10. Unicode Collation Algorithm. Unicode Technical Report. See http://www.unicode.org/reports/tr10/.
UNICODE TR35
Unicode Consortium. Unicode Technical Standard #35. Unicode Locale Data Markup Language. Unicode Technical Report. See http://www.unicode.org/reports/tr35/.
XML 1.0
World Wide Web Consortium. Extensible Markup Language (XML) 1.0. W3C Recommendation. See http://www.w3.org/TR/REC-xml/. The edition of XML 1.0 must be no earlier than the Third Edition; the edition used is implementation-defined, but we recommend that implementations use the latest version.
XML 1.1
Extensible Markup Language (XML) 1.1 (Second Edition), François Yergeau, Eve Maler, John Cowan, et. al., Editors. World Wide Web Consortium, 16 Aug 2006. This version is http://www.w3.org/TR/2006/REC-xml11-20060816. The latest version is available at http://www.w3.org/TR/xml11/.
XML Base
XML Base (Second Edition), Jonathan Marsh and Richard Tobin, Editors. World Wide Web Consortium, 28 Jan 2009. This version is http://www.w3.org/TR/2009/REC-xmlbase-20090128/. The latest version is available at http://www.w3.org/TR/xmlbase/.
xml:id
xml:id Version 1.0, Norman Walsh, Daniel Veillard, and Jonathan Marsh, Editors. World Wide Web Consortium, 09 Sep 2005. This version is http://www.w3.org/TR/2005/REC-xml-id-20050909/. The latest version is available at http://www.w3.org/TR/xml-id/.
Namespaces in XML
Namespaces in XML 1.0 (Third Edition), Dave Hollander, Andrew Layman, Henry S. Thompson, et. al., Editors. World Wide Web Consortium, 08 Dec 2009. This version is http://www.w3.org/TR/2009/REC-xml-names-20091208/. The latest version is available at http://www.w3.org/TR/xml-names.
Namespaces in XML 1.1
Namespaces in XML 1.1 (Second Edition), Dave Hollander, Andrew Layman, Richard Tobin, and Tim Bray, Editors. World Wide Web Consortium, 16 Aug 2006. This version is http://www.w3.org/TR/2006/REC-xml-names11-20060816. The latest version is available at http://www.w3.org/TR/xml-names11/.
XML Schema Part 1
XML Schema Part 1: Structures Second Edition, Henry S. Thompson, David Beech, Murray Maloney, and Noah Mendelsohn, Editors. World Wide Web Consortium, 28 Oct 2004. This version is http://www.w3.org/TR/2004/REC-xmlschema-1-20041028/. The latest version is available at http://www.w3.org/TR/xmlschema-1/.
XML Schema Part 2
XML Schema Part 2: Datatypes Second Edition, Ashok Malhotra and Paul V. Biron, Editors. World Wide Web Consortium, 28 Oct 2004. This version is http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/. The latest version is available at http://www.w3.org/TR/xmlschema-2/.
XML Schema
World Wide Web Consortium. XML Schema Definition Language (XSD) 1.1 Part 1: Structures. W3C Working Draft 3 December 2009. See http://www.w3.org/TR/xmlschema11-1/
XPath 3.0
XML Path Language (XPath) 3.0, Jonathan Robie, Don Chamberlin, Michael Dyck, John Snelson, Editors. World Wide Web Consortium, 22 October 2013. This version is http://www.w3.org/TR/2013/PR-xpath-30-20131022/. The latest version is available at http://www.w3.org/TR/xpath-30/.
XSLT Media Type
World Wide Web Consortium. Registration of MIME Media Type application/xslt+xml. In Appendix B.1 of the XSLT 2.0 specification.

A.2 Other References

DOM Level 2
Document Object Model (DOM) Level 2 Core Specification, Lauren Wood, Arnaud Le Hors, Mike Champion, et. al., Editors. World Wide Web Consortium, 13 Nov 2000. This version is http://www.w3.org/TR/2000/REC-DOM-Level-2-Core-20001113. The latest version is available at http://www.w3.org/TR/DOM-Level-2-Core/.
rfc2119
S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. IETF RFC 2119. See http://www.ietf.org/rfc/rfc2119.txt.
RFC3986
T. Berners-Lee, R. Fielding, and L. Masinter. Uniform Resource Identifiers (URI): Generic Syntax. IETF RFC 3986. See http://www.ietf.org/rfc/rfc3986.txt.
RFC3987
M. Duerst, M. Suignard. Internationalized Resource Identifiers (IRIs). IETF RFC 3987. See http://www.ietf.org/rfc/rfc3987.txt.
STX
Petr Cimprich et al, Streaming Transformations for XML (STX) Version 1.0. Working Draft 27 April 2007. See http://stx.sourceforge.net/documents/spec-stx-20070427.html
XLink
XML Linking Language (XLink) Version 1.0, Steven DeRose, David Orchard, and Eve Maler, Editors. World Wide Web Consortium, 27 Jun 2001. This version is http://www.w3.org/TR/2001/REC-xlink-20010627/. The latest version is available at http://www.w3.org/TR/xlink/.
XML Schema 1.0 and XML 1.1
World Wide Web Consortium. Processing XML 1.1 documents with XML Schema 1.0 processors. W3C Working Group Note 11 May 2005. See http://www.w3.org/TR/2005/NOTE-xml11schema10-20050511/
XML Stylesheet
Associating Style Sheets with XML documents 1.0 (Second Edition), Simon Pieters, James Clark, and Henry S. Thompson, Editors. World Wide Web Consortium, 28 Oct 2010. This version is http://www.w3.org/TR/2010/REC-xml-stylesheet-20101028. The latest version is available at http://www.w3.org/TR/xml-stylesheet.
XPointer Framework
XPointer Framework, Paul Grosso, Eve Maler, Norman Walsh, and Jonathan Marsh, Editors. World Wide Web Consortium, 25 Mar 2003. This version is http://www.w3.org/TR/2003/REC-xptr-framework-20030325/. The latest version is available at http://www.w3.org/TR/xptr-framework/.
XSL-FO
Extensible Stylesheet Language (XSL) Version 1.1, Anders Berglund, Editor. World Wide Web Consortium, 05 Dec 2006. This version is http://www.w3.org/TR/2006/REC-xsl11-20061205/. The latest version is available at http://www.w3.org/TR/xsl11/.
XSLT 1.0
XSL Transformations (XSLT) Version 1.0, James Clark, Editor. World Wide Web Consortium, 16 Nov 1999. This version is http://www.w3.org/TR/1999/REC-xslt-19991116. The latest version is available at http://www.w3.org/TR/xslt.
XSLT 2.0
XSL Transformations (XSLT) Version 2.0 (Second Edition), Michael Kay, Editor. World Wide Web Consortium, 23 January 2007. This version is http://www.w3.org/TR/2007/REC-xslt20-20070123/. The latest version is available at http://www.w3.org/TR/xslt20/.

B XML Representation of JSON

This appendix contains the schema for the XML representation of JSON described in 21.2.1 XML Representation of JSON, together with the stylesheets used for converting from this XML representation to strings matching the JSON grammar.

These schema documents and stylesheets are also available as separate resources (links are listed at the top of this document).

B.1 Schema for the XML Representation of JSON

The schema is reproduced below:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
    elementFormDefault="qualified"
    targetNamespace="http://www.w3.org/2013/XSL/json"
    xmlns:j="http://www.w3.org/2013/XSL/json">
    
    <!-- 
     * This is a schema for the XML representation of JSON used as the target for the
     * XSLT 3.0 function fn:json-to-xml()
     *
     * The schema is made available under the terms of the W3C software notice and license
     * at http://www.w3.org/Consortium/Legal/copyright-software-19980720
     *
    -->
    
    <xs:element name="map" type="j:mapType">
        <xs:unique name="unique-key">
            <xs:selector xpath="*"/>
            <xs:field xpath="@key"/>
        </xs:unique>
    </xs:element>
    
    <xs:element name="array" type="j:arrayType"/>
    
    <xs:element name="string" type="j:stringType"/>
    
    <xs:element name="number" type="j:numberType"/>
    
    <xs:element name="boolean" type="xs:boolean"/>
    
    <xs:element name="null" type="j:nullType"/>
    
    <xs:complexType name="nullType">
        <xs:sequence/>
    </xs:complexType>
    
    <xs:complexType name="stringType">
        <xs:simpleContent>
            <xs:extension base="xs:string">
                <xs:attribute name="escaped" type="xs:boolean" use="optional" default="false"/>
            </xs:extension>
        </xs:simpleContent>
    </xs:complexType>
    
    <xs:simpleType name="numberType">
        <xs:restriction base="xs:double">
            <!-- exclude positive and negative infinity, and NaN -->
            <xs:minExclusive value="-INF"/>
            <xs:maxExclusive value="INF"/>
        </xs:restriction>
    </xs:simpleType>
    
    <xs:complexType name="arrayType">
        <xs:choice minOccurs="0" maxOccurs="unbounded">
            <xs:element ref="j:map"/>
            <xs:element ref="j:array"/>
            <xs:element ref="j:string"/>
            <xs:element ref="j:number"/>
            <xs:element ref="j:boolean"/>
            <xs:element ref="j:null"/>
        </xs:choice>       
    </xs:complexType>
    
    <xs:complexType name="mapType">
        <xs:choice minOccurs="0" maxOccurs="unbounded">
            <xs:element name="map">
                <xs:complexType>
                    <xs:complexContent>
                        <xs:extension base="j:mapType">
                            <xs:attribute name="key" type="xs:string"/>
                        </xs:extension>
                    </xs:complexContent>
                </xs:complexType>
                <xs:unique name="unique-key-2">
                    <xs:selector xpath="*"/>
                    <xs:field xpath="@key"/>
                </xs:unique>
            </xs:element>
            <xs:element name="array">
                <xs:complexType>
                    <xs:complexContent>
                        <xs:extension base="j:arrayType">
                            <xs:attributeGroup ref="j:key-group"/>
                        </xs:extension>
                    </xs:complexContent>
                </xs:complexType>
            </xs:element>
            <xs:element name="string">
                <xs:complexType>
                    <xs:simpleContent>
                        <xs:extension base="j:stringType">
                            <xs:attributeGroup ref="j:key-group"/>
                        </xs:extension>
                    </xs:simpleContent>
                </xs:complexType>
            </xs:element>
            <xs:element name="number">
                <xs:complexType>
                    <xs:simpleContent>
                        <xs:extension base="j:numberType">
                            <xs:attributeGroup ref="j:key-group"/>
                        </xs:extension>
                    </xs:simpleContent>
                </xs:complexType>
            </xs:element>
            <xs:element name="boolean">
                <xs:complexType>
                    <xs:simpleContent>
                        <xs:extension base="xs:boolean">
                            <xs:attributeGroup ref="j:key-group"/>
                        </xs:extension>
                    </xs:simpleContent>
                </xs:complexType>
            </xs:element>
            <xs:element name="null">
                <xs:complexType>
                    <xs:attributeGroup ref="j:key-group"/>
                </xs:complexType>
            </xs:element>
        </xs:choice>
    </xs:complexType>
    
    <xs:attributeGroup name="key-group">
        <xs:attribute name="key" type="xs:string"/>
        <xs:attribute name="escaped-key" type="xs:boolean" use="optional" default="false"/>
    </xs:attributeGroup>
    
</xs:schema>

B.2 Stylesheet for converting XML to JSON (without indentation)

The stylesheet is reproduced below:

<?xml version="1.0" encoding="UTF-8"?>

<xsl:package name="http://www.w3.org/2013/XSLT/xml-to-json.xsl"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:xs="http://www.w3.org/2001/XMLSchema" 
    xmlns:j="http://www.w3.org/2013/XSL/json"
    exclude-result-prefixes="xs j"
    default-mode="j:xml-to-json"
    version="3.0"
    package-version="3.0">
    
    <!-- 
        * This is a stylesheet for converting XML to JSON (with minimal whitespace). 
        * It expects the XML to be in the format produced by the XSLT 3.0 function
        * fn:json-to-xml(), but is designed to be highly customizable.
        *
        * The stylesheet is made available under the terms of the W3C software notice and license
        * at http://www.w3.org/Consortium/Legal/copyright-software-19980720
        *
    -->    

<xsl:stylesheet>

    <!-- The delimiter to be used before and after keys in a map -->
    <xsl:param name="j:key-delimiter" as="xs:string">"</xsl:param>
    
    <!-- The delimiter to be used before and after string values -->
    <xsl:param name="j:string-delimiter" as="xs:string">"</xsl:param>

    <!-- The separator to be used between keys and values -->
    <xsl:param name="j:colon" as="xs:string">:</xsl:param>

    <!-- The separator to be used between entries in a map -->
    <xsl:param name="j:entry-separator" as="xs:string">,</xsl:param>
    
    <!-- The opening delimiter of an array -->
    <xsl:param name="j:start-array" as="xs:string">[</xsl:param>
    
    <!-- The closing delimiter of an array -->
    <xsl:param name="j:end-array" as="xs:string">]</xsl:param>
    
    <!-- The opening delimiter of a map -->
    <xsl:param name="j:start-map" as="xs:string">{</xsl:param>
    
    <!-- The closing delimiter of a map -->
    <xsl:param name="j:end-map" as="xs:string">}</xsl:param>
    
    <!-- The separator to be used between members of an array -->
    <xsl:param name="j:array-separator" as="xs:string" select="$j:comma"/>
    
    <xsl:template name="j:start-array">
        <xsl:value-of select="$j:start-array"/>
    </xsl:template>
    
    <xsl:template name="j:end-array">
        <xsl:value-of select="$j:end-array"/>
    </xsl:template>
    
    <xsl:template name="j:start-map">
        <xsl:value-of select="$j:start-map"/>
    </xsl:template>
    
    <xsl:template name="j:end-map">
        <xsl:value-of select="$j:end-map"/>
    </xsl:template>
    
    <xsl:template name="j:map-separator">
        <xsl:value-of select="$j:map-separator"/>
    </xsl:template>
    
    <xsl:template name="j:array-separator">
        <xsl:value-of select="$j:array-separator"/>
    </xsl:template>
    
    <!-- Entry point: function to convert a supplied XML node to a JSON string -->
    <xsl:function name="j:xml-to-json" as="xs:string" visibility="public">
        <xsl:param name="xml" as="node()"/>
        <xsl:apply-templates select="$xml"/>
    </xsl:function>

    <!-- Conversion of XML to JSON can be achieved by applying templates to the XML root in this mode -->
    <xsl:mode name="j:xml-to-json" streamable="yes" visibility="public" on-no-match="shallow-copy"/>

    <!-- Template rule for j:map elements, representing JSON objects -->
    <xsl:template match="j:map">
        <xsl:call-template name="j:start-map"/>
        <xsl:for-each select="*">
            <xsl:if test="position() gt 1">
                <xsl:call-template name="j:map-separator"/>
            </xsl:if>
            <xsl:apply-templates select="@key"/>
            <xsl:call-template name="j:entry-separator"/>
            <xsl:apply-templates select="."/>
        </xsl:for-each>
        <xsl:call-template name="j:end-map"/>
    </xsl:template>

    <!-- Template rule for j:array elements, representing JSON arrays -->
    <xsl:template match="j:array">
        <xsl:call-template name="j:start-array"/>
        <xsl:for-each select="*">
            <xsl:if test="position() gt 1">
                <xsl:call-template name="j:array-separator"/>
            </xsl:if>
            <xsl:apply-templates select="."/>
        </xsl:for-each>
        <xsl:call-template name="j:end-array"/>
    </xsl:template>

    <!-- Template rule for j:string elements in which special characters are already escaped -->
    <xsl:template match="j:string[@escaped='true']">
        <xsl:value-of select="concat($j:string-delimiter, ., $j:string-delimiter)"/>
    </xsl:template>

    <!-- Template rule for j:string elements in which special characters need to be escaped -->
    <xsl:template match="j:string[not(@escaped='true')]">
        <xsl:value-of select="concat($j:string-delimiter, j:escape(.), $j:string-delimiter)"/>
    </xsl:template>

    <!-- Template rule for j:number and j:boolean elements (representing JSON numbers and booleans) -->
    <xsl:template match="j:number | j:boolean">
        <xsl:value-of select="."/>
    </xsl:template>

    <!-- Template rule for JSON null elements (representing JSON null values) -->
    <xsl:template match="j:null">
        <xsl:text>null</xsl:text>
    </xsl:template>

    <!-- Template rule matching a key within a map where special characters in the key are already escaped -->
    <xsl:template match="j:*/@key[../@key-escaped='true']">
        <xsl:value-of select="concat($j:key-delimiter, ., $j:key-delimiter)"/>
    </xsl:template>

    <!-- Template rule matching a key within a map where special characters in the key need to be escaped -->
    <xsl:template match="j:*/@key[not(../@key-escaped='true')]">
        <xsl:value-of select="concat($j:key-delimiter, j:escape(.), $j:key-delimiter)"/>
    </xsl:template>

    <!-- Template rule matching (and discarding) text nodes in the XML: typically ignorable whitespace -->
    <xsl:template match="text()"/>

    <!-- Function to escape special characters -->
    <xsl:function name="j:escape" as="xs:string">
        <xsl:param name="in" as="xs:string"/>
        <xsl:value-of>
            <xsl:for-each select="string-to-codepoints($in)">
                <xsl:choose>
                    <xsl:when test=". gt 65535">
                        <xsl:value-of select="concat('\u', j:hex4((. - 65536) idiv 1024 + 55296))"/>
                        <xsl:value-of select="concat('\u', j:hex4((. - 65536) mod 1024 + 56320))"/>
                    </xsl:when>
                    <xsl:when test=". = 34">\"</xsl:when>
                    <xsl:when test=". = 92">\\</xsl:when>
                    <xsl:when test=". = 08">\b</xsl:when>
                    <xsl:when test=". = 09">\t</xsl:when>
                    <xsl:when test=". = 10">\n</xsl:when>
                    <xsl:when test=". = 12">\f</xsl:when>
                    <xsl:when test=". = 13">\r</xsl:when>
                    <xsl:when test=". lt 32 or (. ge 127 and . le 160)">
                        <xsl:value-of select="concat('\u', j:hex4(.))"/>
                    </xsl:when>
                    <xsl:otherwise>
                        <xsl:value-of select="codepoints-to-string(.)"/>
                    </xsl:otherwise>
                </xsl:choose>
            </xsl:for-each>
        </xsl:value-of>
    </xsl:function>

    <!-- Function to convert a UTF16 codepoint into a string of four hex digits -->
    <xsl:function name="j:hex4" as="xs:string">
        <xsl:param name="ch" as="xs:integer"/>
        <xsl:variable name="hex" select="'0123456789abcdef'"/>
        <xsl:value-of>
            <xsl:value-of select="substring($hex, $ch idiv 4096 + 1, 1)"/>
            <xsl:value-of select="substring($hex, $ch idiv 256 mod 16 + 1, 1)"/>
            <xsl:value-of select="substring($hex, $ch idiv 16 mod 16 + 1, 1)"/>
            <xsl:value-of select="substring($hex, $ch mod 16 + 1, 1)"/>
        </xsl:value-of>
    </xsl:function>

</xsl:stylesheet>
    
</xsl:package>    

B.3 Stylesheet for converting XML to JSON (with indentation)

The stylesheet is reproduced below:

<?xml version="1.0" encoding="UTF-8"?>


<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
    xmlns:j="http://www.w3.org/2013/XSL/json"
    exclude-result-prefixes="xs j"
    version="2.0">
    
    <!-- 
        * This is a stylesheet for converting XML to JSON (indented for readability). 
        * It expects the XML to be in the format produced by the XSLT 3.0 function
        * fn:json-to-xml(), but is designed to be highly customizable.
        *
        * The stylesheet is made available under the terms of the W3C software notice and license
        * at http://www.w3.org/Consortium/Legal/copyright-software-19980720
        *
    -->    
    
    <xsl:import href="xml-to-json.xsl"/>
    
    <xsl:param name="indent-spaces" as="xs:integer" select="3"/>
    
    <xsl:param name="j:colon" as="xs:string"> : </xsl:param>
    
    <xsl:template name="j:start-array">
        <xsl:text> [&#xa;</xsl:text>
        <xsl:variable name="depth" select="count(ancestor::*)"/>
        <xsl:for-each select="1 to ($depth + 1) * $indent-spaces"><xsl:text> </xsl:text></xsl:for-each>
    </xsl:template>
    
    <xsl:template name="j:end-array">
        <xsl:text> ] </xsl:text>
    </xsl:template>
    
    <xsl:template name="j:start-map">
        <xsl:text> {&#xa;</xsl:text>
        <xsl:variable name="depth" select="count(ancestor::*)"/>
        <xsl:for-each select="1 to ($depth + 1) * $indent-spaces"><xsl:text> </xsl:text></xsl:for-each>
    </xsl:template>
    
    <xsl:template name="j:end-map">
        <xsl:text> } </xsl:text>
    </xsl:template>
   
    <xsl:template name="j:map-separator">
        <xsl:variable name="depth" select="count(ancestor::*)"/>
        <xsl:text>,&#xa;</xsl:text>
        <xsl:for-each select="1 to $depth * $indent-spaces"><xsl:text> </xsl:text></xsl:for-each>
    </xsl:template>
    
    <xsl:template name="j:array-separator">
        <xsl:variable name="depth" select="count(ancestor::*)"/>
        <xsl:text>,&#xa;</xsl:text>
        <xsl:for-each select="1 to $depth * $indent-spaces"><xsl:text> </xsl:text></xsl:for-each>
    </xsl:template>
    
</xsl:stylesheet>

C Glossary (Non-Normative)

absent

A component of the context that has no value is said to be absent.

absorption

An operand usage of absorption indicates that the construct reads the subtree(s) rooted at a supplied node(s).

accumulator

An accumulator defines a value that is computed progressively while processing the nodes of a document in document order. The value for a given node is available via a pair of functions, one giving the value for a node before processing its descendants, and one giving the value for the same node after processing its descendants.

accumulator function

The functions accumulator-before and accumulator-after are referred to as the accumulator functions.

alias

A stylesheet can use the xsl:namespace-alias element to declare that a literal namespace URI is being used as an alias for a target namespace URI.

arity

The arity of a stylesheet function is the number of xsl:param elements in the function definition.

atomize

The term atomization is defined in Section 2.4.2 Atomization XP30. It is a process that takes as input a sequence of items, and returns a sequence of atomic values, in which the nodes are replaced by their typed values as defined in [Data Model].

attribute set

An attribute set is defined as a set of xsl:attribute-set declarations in the same package that share the same expanded QName.

attribute value template

In an attribute that is designated as an attribute value template, such as an attribute of a literal result element, an expression can be used by surrounding the expression with curly brackets ({}), following the general rules for value templates

backwards compatible behavior

An element is processed with backwards compatible behavior if its effective version is less than 3.0.

base output URI

The base output URI is a URI to be used as the base URI when resolving a relative URI reference allocated to a final result tree. If the transformation generates more than one final result tree, then typically each one will be allocated a URI relative to this base URI.

basic XSLT processor

A basic XSLT processor is an XSLT processor that implements all the mandatory requirements of this specification with the exception of constructs explicitly associated with an optional feature.

character map

A character map allows a specific character appearing in a text or attribute node in the final result tree to be substituted by a specified string of characters during serialization.

choice operand group

For some construct kinds, one or more operand roles may be defined to form a choice operand group. This concept is used where it is known that operands are mutually exclusive (for example the then and else clauses in a conditional expression).

circularity

A circularity is said to exist if a construct such as a global variable, an attribute set, or a key, is defined in terms of itself. For example, if the expression or sequence constructor specifying the value of a global variable X references a global variable Y, then the value for Y must be computed before the value of X. A circularity exists if it is impossible to do this for all global variable definitions.

climbing

Climbing: indicates that nodes returned by the construct are reached by navigating the parent, ancestor[-or-self], attribute, and/or namespace axes from the node at the current streaming position.

collation

Facilities in XSLT 3.0 and XPath 3.0 that require strings to be ordered rely on the concept of a named collation. A collation is a set of rules that determine whether two strings are equal, and if not, which of them is to be sorted before the other.

combined posture

The combined posture of a choice operand group is determined by the postures of the operands in the group, and is the first of the following that applies:

compatible

The signatures of two components are compatible if they present the same interface to the user of the component. The additional rules depend on the kind of component.

component

The term component is used to refer to any of the following: a stylesheet function, a named template, a mode, an accumulator an attribute set, a key, global variable, or a mode.

composite merge key value

The ordered collection of merge key values computed for one item in a merge input sequence (one for each merge key component within the merge key specification) is referred to as a composite merge key value.

construct

The term construct refers to the union of the following: a sequence constructor, an instruction, an attribute set, a value template, an expression, or a pattern.

consuming

A consuming construct is any construct deemed consuming by the rules in this section (19 Streamability).

containing package

A component declaration results in multiple components, one in the package in which the declaration appears, and potentially one in each package that uses the declaring package, directly or indirectly, subject to the visibility of the component. Each of these multiple compenents has the same declaring package, but each has a different containing package. For the original component, the declaring package and the containing package are the same; for a copy of a component made as a result of a xsl:use-package declaration, the declaring package will be the original package, and the containing package will be the package in which the xsl:use-package declaration appears.

context item

The context item is the item currently being processed. An item (see [Data Model]) is either an atomic value (such as an integer, date, or string), a node, or a function item. The context item is initially set to the initial context item supplied when the transformation is invoked (see 2.3 Initiating a Transformation). It changes whenever instructions such as xsl:apply-templates and xsl:for-each are used to process a sequence of items; each item in such a sequence becomes the context item while that item is being processed.

context item type

For every expression, it is possible to establish by static analysis, information about the item type of the context item for evaluation of that expression. This is called the context item type of the expression.

context node

If the context item is a node (as distinct from an atomic value such as an integer), then it is also referred to as the context node. The context node is not an independent variable, it changes whenever the context item changes. When the context item is an atomic value or a function item, there is no context node.

context position

The context position is the position of the context item within the sequence of items currently being processed. It changes whenever the context item changes. When an instruction such as xsl:apply-templates or xsl:for-each is used to process a sequence of items, the first item in the sequence is processed with a context position of 1, the second item with a context position of 2, and so on.

context posture

The context posture. This captures information about how the context item used as input to the construct is positioned relative to the streamed input. The context posture of a construct C is the posture of the expression whose value sets the focus for the evaluation of C.

context size

The context size is the number of items in the sequence of items currently being processed. It changes whenever instructions such as xsl:apply-templates and xsl:for-each are used to process a sequence of items; during the processing of each one of those items, the context size is set to the count of the number of items in the sequence (or equivalently, the position of the last item in the sequence).

controlled operand

Within a focus-changing construct there are one or more operands that are evaluated with a focus determined by the controlling operand (or in some cases such as xsl:on-completion, with an absent focus); these are referred to as controlled operands.

controlling operand

Within a focus-changing construct there is in many cases one operand whose value determines the focus for evaluating other operands; this is referred to as the controlling operand.

core function

The term core function means a function that is specified in [Functions and Operators] and that is in the standard function namespace.

crawling

Crawling: typically indicates that nodes returned by a construct are reached by navigating the descendant[-or-self] axis.

current captured substrings

While the xsl:matching-substring instruction is active, a set of current captured substrings is available, corresponding to the parenthesized sub-expressions of the regular expression.

current group

The evaluation context for XPath expressions includes a component called the current group, which is a sequence.

current group value

The current group value is the group itself, as a sequence of items

current grouping key

The evaluation context for XPath expressions includes a component called the current grouping key, which is a sequence of atomic values. The current grouping key is the grouping key shared in common by all the items within the current group.

current grouping key value

The current grouping key value is a single atomic value, or in the case of a composite key, a sequence of atomic values, containing the grouping key of the items in the current group value.

current mode

At any point in the processing of a stylesheet, there is a current mode. When the transformation is initiated, the current mode is the initial mode, as described in 2.3 Initiating a Transformation. Whenever an xsl:apply-templates instruction is evaluated, the current mode becomes the mode selected by this instruction.

current template rule

At any point in the processing of a stylesheet, there may be a current template rule. Whenever a template rule is chosen as a result of evaluating xsl:apply-templates, xsl:apply-imports, or xsl:next-match, the template rule becomes the current template rule for the evaluation of the rule's sequence constructor. When an xsl:for-each, xsl:for-each-group, xsl:analyze-string, xsl:iterate, xsl:stream, xsl:merge, or xsl:evaluate instruction is evaluated, or when evaluating a sequence constructor contained in an xsl:sort or xsl:key element, or when a non-contextual function call is made, the current template rule becomes absent for the evaluation of that instruction or function.

decimal format

All the xsl:decimal-format declarations in a package that share the same name are grouped into a named decimal format; those that have no name are grouped into a single unnamed decimal format.

declaration

Top-level elements fall into two categories: declarations, and user-defined data elements. Top-level elements whose names are in the XSLT namespace are declarations. Top-level elements in any other namespace are user-defined data elements (see 3.8.3 User-defined Data Elements)

declaration order

The declarations within a stylesheet level have a total ordering known as declaration order. The order of declarations within a stylesheet level is the same as the document order that would result if each stylesheet module were inserted textually in place of the xsl:include element that references it.

declaring package

The declaring package of a component is the package that contains the declaration (or, in the case of xsl:attribute-set and xsl:key, multiple declarations) of the component.

default collation

In this specification the term default collation means the collation that is used by XPath operators such as eq and lt appearing in XPath expressions within the stylesheet.

default priority

If no priority attribute is specified on an xsl:template element, a default priority is computed, based on the syntax of the pattern supplied in the match attribute.

defining element

A string in the form of a lexical QName may occur as the value of an attribute node in a stylesheet module, or within an XPath expression contained in an attribute or text node within a stylesheet module, or as the result of evaluating an XPath expression contained in such a node. The element containing this attribute or text node is referred to as the defining element of the lexical QName.

deprecated

Some constructs defined in this specification are described as being deprecated. The use of this term implies that stylesheet authors should not use the construct, and that the construct may be removed in a later version of this specification.

dynamic error

An error that is not detected until a source document is being transformed is referred to as a dynamic error.

dynamic evaluation feature

A processor that claims conformance with the dynamic evaluation feature must evaluate the xsl:evaluate function as described in this specification.

effective value

The result of evaluating a value template is referred to as its effective value.

effective version

The effective version of an element in a stylesheet module or package manifest is the decimal value of the [xsl:]version attribute (see 3.5 Standard Attributes) on that element or on the innermost ancestor element that has such an attribute, excluding the version attribute on an xsl:output element.

embedded stylesheet module

An embedded stylesheet module is a stylesheet module that is embedded within another XML document, typically the source document that is being transformed.

EQName

An EQName is a string representing a expanded QName where the string, after removing leading and trailing whitespace, is in the form defined by the EQNameXP30 production in the XPath specification.

expanded QName

An expanded QName is a value in the value space of the xs:QName datatype as defined in the XDM data model (see [Data Model]): that is, a triple containing namespace prefix (optional), namespace URI (optional), and local name. Two expanded QNames are equal if the namespace URIs are the same (or both absent) and the local names are the same. The prefix plays no part in the comparison, but is used only if the expanded QName needs to be converted back to a string.

exposed visibility

The exposed visibility of a component is established by an xsl:expose element in the package manifest.

expression

Within this specification, the term XPath expression, or simply expression, means a string that matches the production ExprXP30 defined in [XPath 3.0].

extension attribute

An element from the XSLT namespace may have any attribute not from the XSLT namespace, provided that the expanded QName (see [XPath 3.0]) of the attribute has a non-null namespace URI. These attributes are referred to as extension attributes.

extension function

An extension function is a function that is available for use within an XPath expression, other than a core function defined in [Functions and Operators], an additional function defined in this XSLT specification, a constructor function named after an atomic type, or a stylesheet function defined using an xsl:function declaration.

extension instruction

An extension instruction is an element within a sequence constructor that is in a namespace (not the XSLT namespace) designated as an extension namespace.

extension namespace

The extension instruction mechanism allows namespaces to be designated as extension namespaces. When a namespace is designated as an extension namespace and an element with a name from that namespace occurs in a sequence constructor, then the element is treated as an instruction rather than as a literal result element.

final output state

The first of the two output states is called final output state. This state applies when instructions are writing to a final result tree.

final result tree

A final result tree is a result tree that forms part of the final output of a transformation. Once created, the contents of a final result tree are not accessible within the stylesheet itself.

focus

When a sequence constructor is evaluated, the processor keeps track of which items are being processed by means of a set of implicit variables referred to collectively as the focus.

focus-changing construct

A focus-changing construct is a construct that has one or more operands that are evaluated with a different focus from the parent construct.

focus-setting container

The focus-setting container of a construct C is the innermost focus-changing construct F (if one exists) such that C is directly or indirectly contained in a controlled operand of F. If there is no such construct F, then the focus-setting container is the containing declaration, for example an xsl:function or xsl:template element.

forwards compatible behavior

An element is processed with forwards compatible behavior if its effective version is greater than 3.0.

free-ranging

A free-ranging construct is any construct deemed free-ranging by the rules in this section (19 Streamability).

function conversion rules

Except where otherwise indicated, the actual value of an expression is converted to the required type using the function conversion rules. These are the rules defined in [XPath 3.0] for converting the supplied argument of a function call to the required type of that argument, as defined in the function signature. The relevant rules are those that apply when XPath 1.0 compatibility mode is set to false.

function parameter

An xsl:param element may appear as a child of an xsl:function element, before any non-xsl:param children of that element. Such a parameter is known as a function parameter. A function parameter is a local variable with the additional property that its value can be set when the function is called, using a function call in an XPath expression.

general streamability rules

Many constructs share the same streamability rules. These rules, referred to as the general streamability rules, are defined here.

global variable

A top-level variable-binding element declares a global variable that is visible everywhere (except within its own declaration, and where it is shadowed by another binding).

grounded

Grounded: indicates that the value returned by the construct does not contain nodes from the streamed input document

group

The xsl:for-each-group instruction allocates the items in an input sequence into groups of items (that is, it establishes a collection of sequences) based either on common values of a grouping key, or on a pattern that the initial or final item in a group must match.

grouping key

If either of the group-by or group-adjacent attributes is present, then for each item in the population a set of grouping keys is calculated, as follows: the expression contained in the group-by or group-adjacent attribute is evaluated; the result is atomized; and any xs:untypedAtomic values are cast to xs:string. If composite="yes" is specified, there is a single grouping key whose value is the resulting sequence; otherwise, there is a set of grouping keys, consisting of the distinct atomic values present in the result sequence.

guaranteed-streamable

A guaranteed-streamable construct is a construct that is declared to be streamable and that follows the particular rules for that construct to make streaming possible, as defined by the analysis in this specification.

higher-order operand

Whether or not the operand is higher-order. For this purpose an operand O of a construct C is higher-order if the semantics of C potentially require O to be evaluated more than once during a single evaluation of C.

homonymous

Two components are said to be homonymous if they have the same symbolic identifier.

identical (types)

Types S and T are considered identical for the purpose of these rules if and only if subtype(S, T) and subtype(T, S) both hold, where the subtype relation is defined in Section 2.5.6.1 The judgement subtype(A, B) XP30.

implementation

A specific product that performs the functions of an XSLT processor is referred to as an implementation.

implementation-defined

In this specification, the term implementation-defined refers to a feature where the implementation is allowed some flexibility, and where the choices made by the implementation must be described in documentation that accompanies any conformance claim.

implementation-dependent

The term implementation-dependent refers to a feature where the behavior may vary from one implementation to another, and where the vendor is not expected to provide a full specification of the behavior.

import precedence

A declaration D in the stylesheet is defined to have lower import precedence than another declaration E if the stylesheet level containing D would be visited before the stylesheet level containing E in a post-order traversal of the import tree (that is, a traversal of the import tree in which a stylesheet level is visited after its children). Two declarations within the same stylesheet level have the same import precedence.

import tree

The stylesheet levels making up a stylesheet are treated as forming an import tree. In the import tree, each stylesheet level has one child for each xsl:import declaration that it contains.

in-scope schema component

The schema components that may be referenced by name in a stylesheet are referred to as the in-scope schema components. This set is the same throughout all the modules of a stylesheet.

initial context item

An item that acts as the initial context item for the transformation. This item is accessible within the stylesheet as the initial value of the XPath expressions . (dot) and self::node(), as described in 5.4.3.1 Maintaining Position: the Focus

initial function

The transformation is performed by evaluating an initial function.

initial item

For each group, the item within the group that is first in population order is known as the initial item of the group.

initial mode

The initial mode, if specified, must either be the default mode, or a mode that is explicitly named either in an xsl:mode declaration, or in the mode attribute of an xsl:template declaration within the stylesheet. If an initial mode is supplied, then in searching for the template rule that best matches the initial context item, the processor considers only those rules that apply to the initial mode. If no initial mode is supplied, then the mode used is that named in the default-mode attribute of the xsl:stylesheet element of the principal stylesheet module; or failing that, the mode named in the default-mode attribute of its containing xsl:package element; or in the absence of such an attribute, the unnamed mode.

initial sequence

The sequence to be sorted is referred to as the initial sequence.

initial template

The transformation is performed by evaluating an initial template. If a named template is supplied when the transformation is initiated, then this is the initial template; otherwise, the initial template is the template rule selected according to the rules of the xsl:apply-templates instruction for processing the initial context item in the initial mode.

inspection

An operand usage of inspection indicates that the construct accesses properties of a supplied node that are available without reading its subtree.

instruction

An instruction is either an XSLT instruction or an extension instruction.

key

A key is defined as a set of xsl:key declarations in the same package that share the same name.

key specifier

The expression in the use attribute and the sequence constructor within an xsl:key declaration are referred to collectively as the key specifier. The key specifier determines the values that may be used to find a node using this key.

lexical QName

A lexical QName is a string representing a expanded QName where the string, after removing leading and trailing whitespace, is within the lexical space of the xs:QName datatype as defined in XML Schema (see [XML Schema Part 2]): that is, a local name optionally preceded by a namespace prefix and a colon.

literal namespace URI

A namespace URI in the stylesheet tree that is being used to specify a namespace URI in the result tree is called a literal namespace URI.

literal result element

In a sequence constructor, an element in the stylesheet that does not belong to the XSLT namespace and that is not an extension instruction (see 23.2 Extension Instructions) is classified as a literal result element.

local variable

As well as being allowed as a declaration, the xsl:variable element is also allowed in sequence constructors. Such a variable is known as a local variable.

map

A map consists of a set of entries. Each entry comprises a key which is an arbitrary atomic value, and an arbitrary sequence called the associated value.

match type

The match type of a pattern is the most specific ItemType that is known to match all items that the pattern can match.

merge activation

A merge activation is a single evaluation of the sequence constructor contained within the xsl:merge-action element, which occurs once for each distinct composite merge key value.

merge input sequence

A merge input sequence is an arbitrary sequenceDM30 of items which is already sorted according to the merge key specification for the corresponding merge source definition.

merge key component

A merge key component specifies one component of a merge key specification; it corresponds to a single xsl:merge-key element in the stylesheet.

merge key specification

A merge key specification consists of one or more adjacent xsl:merge-key elements which together define how the merge input sequences selected by a merge source definition are sorted. Each xsl:merge-key element defines one merge key component.

merge key value

For each item in a merge input sequence, a value is computed for each merge key component within the merge key specification. The value computed for an item by using the Nth merge key component is referred to as the Nth merge key value of that item.

merge source definition

A merge source definition is the definition of one kind of input to the merge operation. It selects zero or more merge input sequences, and it includes a merge key specification to define how the merge key values are computed for each such merge input sequence.

mode

Modes allow a node in a source tree to be processed multiple times, each time producing a different result. They also allow different sets of template rules to be active when processing different trees, for example when processing documents loaded using the document function (see 20.1 fn:document) or when processing temporary trees.

mode definition

All the xsl:mode declarations in a stylesheet that share the same name are grouped into a named mode definition; those that have no name are grouped into a single unnamed mode definition.

motionless

A motionless construct is any construct deemed motionless by the rules in this section (19 Streamability).

named template

Templates can be invoked by name. An xsl:template element with a name attribute defines a named template.

namespace fixup

The rules for the individual XSLT instructions that construct a result tree (see 11 Creating Nodes and Sequences) prescribe some of the situations in which namespace nodes are written to the tree. These rules, however, are not sufficient to ensure that the prescribed constraints are always satisfied. The XSLT processor must therefore add additional namespace nodes to satisfy these constraints. This process is referred to as namespace fixup.

navigation

An operand usage of navigation indicates that the construct may navigate freely from the supplied node to other nodes in the same tree, in a way that is not constrained by the streamability rules.

non-contextual function call

The term non-contextual function call is used to refer to function calls that do not pass the dynamic context to the called function. This includes all calls on stylesheet functions and all dynamic function invocationsXP30, (that is calls to function items as permitted by XPath 3.0). It does not include calls to all core functions in particular those that explicitly depend on the context, such as the current-group and regex-group functions. It is implementation-defined whether, and under what circumstances, calls to extension functions are non-contextual.

non-positional predicate

A predicate is a non-positional predicate if it satisfies both of the following conditions:

non-schema-aware processor

A non-schema-aware processor is a processor that does not claim conformance with the schema-aware conformance feature. Such a processor must handle constructs associated with schema-aware processing as described in this section.

operand

In an actual instance of a construct, there will be a number of operands.

operand role

For every construct kind, there is a set of zero or more operand roles.

operand usage

The operand usage. This gives information, in the case where the operand value contains nodes, about how those nodes are used. The operand usage takes one of the values absorption, inspection, transmission, or navigation.

order of first appearance

There is a total ordering among groups referred to as the order of first appearance. A group G is defined to precede a group H in order of first appearance if the initial item of G precedes the initial item of H in population order. If two groups G and H have the same initial item (because the item is in both groups) then G precedes H if the grouping key of G precedes the grouping key of H in the sequence that results from evaluating the group-by expression of this initial item.

output definition

All the xsl:output declarations within a package that share the same name are grouped into a named output definition; those that have no name are grouped into a single unnamed output definition.

output state

Each instruction in the stylesheet is evaluated in one of two possible output states: final output state or temporary output state

override

A component in a using package may override a component in a used package, provided that the visibility of the component in the used package is either abstract or public. The overriding declaration is written as a child of the xsl:override element, which in turn appears as a child of xsl:use-package.

package

A package is represented by an xsl:package element, which will generally be the outermost element of an XML document.

package manifest

The content of the xsl:package element is referred to as the package manifest

parameter

The xsl:param element declares a parameter, which may be a stylesheet parameter, a template parameter, a function parameter, or an xsl:iterate parameter. A parameter is a variable with the additional property that its value can be set by the caller.

pattern

A pattern specifies a set of conditions on an item. An item that satisfies the conditions matches the pattern; an item that does not satisfy the conditions does not match the pattern.

picture string

The picture string is the string supplied as the second argument of the format-numberFO30 function.

place marker

The xsl:number instruction performs two tasks: firstly, determining a place marker (this is a sequence of integers, to allow for hierarchic numbering schemes such as 1.12.2 or 3(c)ii), and secondly, formatting the place marker for output as a text node in the result sequence.

population

The sequence of items to be grouped, which is referred to as the population, is determined by evaluating the XPath expression contained in the select attribute.

population order

The population is treated as a sequence; the order of items in this sequence is referred to as population order

post-descent instruction

A motionless instruction having no consuming instruction as a following sibling is referred to as a post-descent instruction.

posture

The posture of the expression. This captures information about the way in which the streamed input document is positioned on return from evaluating the construct. The posture takes one of the values climbing, striding, crawling, roaming, or grounded.

potential visibility

The potential visibility of a component is established when the component is declared or accepted into a package.

potentially consuming

An operand is potentially consuming if either or both of the following conditions applies:

pre-descent instruction

A motionless instruction having no consuming instruction as a preceding sibling is referred to as a pre-descent instruction.

principal stylesheet module

For a given transformation, one stylesheet module functions as the principal stylesheet module. The complete stylesheet is assembled by finding the stylesheet modules referenced directly or indirectly from the principal stylesheet module using xsl:include and xsl:import elements: see 3.12.2 Stylesheet Inclusion and 3.12.3 Stylesheet Import.

priority

The priority of a template rule is specified by the priority attribute on the xsl:template declaration. If no priority is specified explicitly for a template rule, its default priority is used, as defined in 6.5 Default Priority for Template Rules.

processing order

There is another total ordering among groups referred to as processing order. If group R precedes group S in processing order, then in the result sequence returned by the xsl:for-each-group instruction the items generated by processing group R will precede the items generated by processing group S.

processor

The software responsible for transforming source trees into result trees using an XSLT stylesheet is referred to as the processor. This is sometimes expanded to XSLT processor to avoid any confusion with other processors, for example an XML processor.

raw result

The result of invoking the selected component, after any required conversion to the declared result type of the component, is referred to as the raw result.

reference resolution

The process of identifying the component to which a symbolic reference applies (possibly chosen from several homonymous alternatives) is called reference binding.

required type

The context within a stylesheet where an XPath expression appears may specify the required type of the expression. The required type indicates the type of the value that the expression is expected to return.

reserved namespace

The XSLT namespace, together with certain other namespaces recognized by an XSLT processor, are classified as reserved namespaces and must be used only as specified in this and related specifications.

result tree

The term result tree is used to refer to any tree constructed by instructions in the stylesheet. A result tree is either a final result tree or a temporary tree.

roaming

Roaming: indicates that the nodes returned by an expression could be anywhere in the tree, which inevitably means that the construct cannot be evaluated using streaming.

same key

Within a map, no two entries have the same key. Two atomic values K1 and K2 are the same key for this purpose if the relation deep-equal(K1, K2, $UCC) holds, where $UCC is the Unicode codepoint collation.

schema component

Type definitions and element and attribute declarations are referred to collectively as schema components.

schema instance namespace

The schema instance namespace http://www.w3.org/2001/XMLSchema-instance is used as defined in [XML Schema Part 1]

schema namespace

The schema namespace http://www.w3.org/2001/XMLSchema is used as defined in [XML Schema Part 1]

schema-aware XSLT processor

A schema-aware XSLT processor is an XSLT processor that implements the mandatory requirements of this specification connected with the xsl:import-schema declaration, the [xsl:]validation and [xsl:]type attributes, and the ability to handle input documents whose nodes have type annotations other than xs:untyped and xs:untypedAtomic. The mandatory requirements of this specification are taken to include the mandatory requirements of XPath 3.0, as described in [XPath 3.0]. A requirement is mandatory unless the specification includes wording (such as the use of the words should or may) that clearly indicates that it is optional.

sequence constructor

A sequence constructor is a sequence of zero or more sibling nodes in the stylesheet that can be evaluated to return a sequence of nodes, atomic values, and function items. The way that the resulting sequence is used depends on the containing instruction.

serialization

A frequent requirement is to output a final result tree as an XML document (or in other formats such as HTML). This process is referred to as serialization.

serialization error

If a transformation has successfully produced a final result tree, it is still possible that errors may occur in serializing the result tree. For example, it may be impossible to serialize the result tree using the encoding selected by the user. Such an error is referred to as a serialization error.

serialization feature

A processor that claims conformance with the serialization feature must support the conversion of a final result tree to a sequence of octets following the rules defined in 25 Serialization.

shadows

A binding shadows another binding if the binding occurs at a point where the other binding is visible, and the bindings have the same name.

simplified stylesheet module

A simplified stylesheet module is a tree, or part of a tree, consisting of a literal result element together with its descendant nodes and associated attributes and namespaces. This element is not itself in the XSLT namespace, but it must have an xsl:version attribute, which implies that it must have a namespace node that declares a binding for the XSLT namespace. For further details see 3.9 Simplified Stylesheet Modules.

singleton focus

A singleton focus based on an item J has the context item (and therefore the context node, if J is a node) set to J, and the context position and context size both set to 1 (one).

snapshot

A snapshot of a node N is a deep copy of N, as produced by the xsl:copy-of instruction with copy-namespaces set to yes and validation set to preserve, with the additional property that for every ancestor of N, the copy also has a corresponding ancestor whose name, node-kind, and base URI are the same as the corresponding ancestor of N, and that has copies of the attributes and namespaces of the corresponding ancestor of N. But the ancestor has a type annotation of xs:anyType, has the properties nilled, is-id, and is-idref set to false, and has no children other than the child that is a copy of N or one of its ancestors.

sort key component

Within a sort key specification, each xsl:sort element defines one sort key component.

sort key specification

A sort key specification is a sequence of one or more adjacent xsl:sort elements which together define rules for sorting the items in an input sequence to form a sorted sequence.

sort key value

For each item in the initial sequence, a value is computed for each sort key component within the sort key specification. The value computed for an item by using the Nth sort key component is referred to as the Nth sort key value of that item.

sorted sequence

The sequence after sorting as defined by the xsl:sort elements is referred to as the sorted sequence.

source tree

The term source tree means any tree provided as input to the transformation. This includes the document containing the initial context item if any, documents containing nodes supplied as the values of stylesheet parameters, documents obtained from the results of functions such as document, docFO30, and collectionFO30, documents read using the xsl:stream instruction, and documents returned by extension functions or extension instructions. In the context of a particular XSLT instruction, the term source tree means any tree provided as input to that instruction; this may be a source tree of the transformation as a whole, or it may be a temporary tree produced during the course of the transformation.

stable

A sort key specification is said to be stable if its first xsl:sort element has no stable attribute, or has a stable attribute whose effective value is yes.

standalone stylesheet module

A standalone stylesheet module is a stylesheet module that comprises the whole of an XML document.

standard attributes

There are a number of standard attributes that may appear on any XSLT element: specifically default-collation, default-mode, default-validation, exclude-result-prefixes, expand-text, extension-element-prefixes, use-when, version, and xpath-default-namespace.

standard error namespace

The standard error namespace http://www.w3.org/2005/xqt-errors is used for error codes defined in this specification and related specifications. It is also used for the names of certain predefined variables accessible within the scope of an xsl:catch element.

standard function namespace

The standard function namespace http://www.w3.org/2005/xpath-functions is used for functions in the function library defined in [Functions and Operators] and for standard functions defined in this specification.

standard stylesheet module

A standard stylesheet module is a tree, or part of a tree, consisting of an xsl:stylesheet or xsl:transform element (see 3.8 Stylesheet Element) together with its descendant nodes and associated attributes and namespaces.

static error

An error that can be detected by examining a stylesheet before execution starts (that is, before the source document and values of stylesheet parameters are available) is referred to as a static error.

static expression

A static expression is an XPath expression whose value must be computed during static analysis of the stylesheet.

static parameter

A static variable declared using an xsl:param element is referred to as a static parameter.

static variable

A top-level variable-binding element having the attribute static="yes" declares a static variable: that is, a global variable whose value is known during static analysis of the stylesheet.

streamable mode

A streamable mode is a mode that is declared in an xsl:mode declaration with the attribute streamable="yes".

streamed document

A streamed document is a source tree that is processed using streaming, that is, without constructing a complete tree of nodes in memory.

streamed node

A streamed node is a node in a streamed document.

streaming

The term streaming refers to a manner of processing in which documents (such as source and result documents) are not represented by a complete tree of nodes occupying memory proportional to document size, but instead are processed "on the fly" as a sequence of events, similar in concept to the stream of events notified by an XML parser to represent markup in lexical XML.

streaming feature

A processor that claims conformance with the streaming feature must use streamed processing in cases where (a) streaming is requested (for example by using the attribute streamable="yes" on xsl:mode, or the xsl:stream instruction) and (b) the constructs in question are guaranteed-streamable according to this specification.

striding

Striding: indicates that the result of a construct is a sequence of nodes, in document order, that are peers in the sense that none of them is an ancestor or descendant of any other.

string value

The term string value is defined in Section 5.13 string-value Accessor DM30. Every node has a string value. For example, the string value of an element is the concatenation of the string values of all its descendant text nodes.

stylesheet

A transformation in the XSLT language is expressed in the form of a stylesheet, whose syntax is well-formed XML [XML 1.0] conforming to the Namespaces in XML Recommendation [Namespaces in XML].

stylesheet function

An xsl:function declaration declares the name, parameters, and implementation of a stylesheet function that can be called from any XPath expression within the stylesheet.

stylesheet level

A stylesheet level is a collection of stylesheet modules connected using xsl:include declarations: specifically, two stylesheet modules A and B are part of the same stylesheet level if one of them includes the other by means of an xsl:include declaration, or if there is a third stylesheet module C that is in the same stylesheet level as both A and B.

stylesheet module

A package consists of one or more stylesheet modules, each one forming all or part of an XML document.

stylesheet parameter

A top-level xsl:param element declares a stylesheet parameter. A stylesheet parameter is a global variable with the additional property that its value can be supplied by the caller when a transformation is initiated.

supplied value

The value of the variable is computed using the expression given in the select attribute or the contained sequence constructor, as described in 9.3 Values of Variables and Parameters. This value is referred to as the supplied value of the variable.

sweep

Every construct has a sweep, which is a measure of the extent to which the current position in the input stream moves during the evaluation of the expression. The sweep is one of: motionless, consuming, or free-ranging .

symbolic identifier

The symbolic identifier of a component is a composite name used to identify the component uniquely within a package. The symbolic identifier comprises the kind of component (stylesheet function, named template, accumulator, attribute set, global variable, or mode), the expanded QName of the component (namespace URI plus local name), and in the case of stylesheet functions, the arity.

symbolic reference

The declaration of a component includes constructs that can be interpreted as references to other components by means of their symbolic identifiers. These constructs are generically referred to as symbolic references. Examples of constructs that give rise to symbolic references are the name attribute of xsl:call-template; the [xsl:]use-attribute-sets attribute of xsl:copy, xsl:element, and literal result elements; the mode attribute of xsl:template and xsl:apply-templates; XPath variable references referring to global variables; and XPath function calls referring to stylesheet functions or accumulator functions.

tail position

An instruction J is in a tail position within a sequence constructor SC if it satisfies one of the following conditions:

target expression

The string that results from evaluating the expression in the xpath attribute is referred to as the target expression.

target namespace URI

The namespace URI that is to be used in the result tree as a substitute for a literal namespace URI is called the target namespace URI.

template

An xsl:template declaration defines a template, which contains a sequence constructor ; this sequence constructor is evaluated to determine the result of the template. A template can serve either as a template rule, invoked by matching items against a pattern, or as a named template, invoked explicitly by name. It is also possible for the same template to serve in both capacities.

template parameter

An xsl:param element may appear as a child of an xsl:template element, before any non-xsl:param children of that element. Such a parameter is known as a template parameter. A template parameter is a local variable with the additional property that its value can be set when the template is called, using any of the instructions xsl:call-template, xsl:apply-templates, xsl:apply-imports, or xsl:next-match.

template rule

A stylesheet contains a set of template rules (see 6 Template Rules). A template rule has three parts: a pattern that is matched against nodes, a (possibly empty) set of template parameters, and a sequence constructor that is evaluated to produce a sequence of items.

temporary output state

The second of the two output states is called temporary output state. This state applies when instructions are writing to a temporary tree or any other non-final destination.

temporary tree

The term temporary tree means any tree that is neither a source tree nor a final result tree.

text value template

In a text node that is designated as a text value template, expressions can be used by surrounding each expression with curly brackets ({}).

top-level

An element occurring as a child of an xsl:stylesheet, xsl:transform, or xsl:override element is called a top-level element.

transmission

An operand usage of transmission indicates that the construct will (potentially) return a supplied node as part of its result to the calling construct (that is, to its parent in the construct tree).

traversal

A traversal of a tree is a sequence of traversal events.

traversal-event

a traversal event (shortened to event in this section) is a pair comprising a phase (start or end) and a node.

tunnel parameter

A parameter passed to a template may be defined as a tunnel parameter. Tunnel parameters have the property that they are automatically passed on by the called template to any further templates that it calls, and so on recursively.

type annotation

The term type annotation is used in this specification to refer to the value returned by the dm:type-name accessor of a node: see Section 5.14 type-name Accessor DM30.

type error

Certain errors are classified as type errors. A type error occurs when the value supplied as input to an operation is of the wrong type for that operation, for example when an integer is supplied to an operation that expects a node.

type-determined usage

The type-determined usage of an operand is as follows: if the required type (ignoring occurrence indicator) is function(*) or a subtype thereof, then inspection; if the required type (ignoring occurrence indicator) is xs:anyAtomicType or a subtype thereof, then absorption; otherwise navigation.

typed value

The term typed value is defined in Section 5.15 typed-value Accessor DM30. Every node, other than an element whose type annotation identifies it as having element-only content, has a typed value. For example, the typed value of an attribute of type xs:IDREFS is a sequence of zero or more xs:IDREF values.

unnamed mode

There is always an unnamed mode available. The unnamed mode is the default mode used when no mode attribute is specified on an xsl:apply-templates instruction or xsl:template declaration, unless a different default mode has been specified using the [xsl:]default-mode attribute of a containing element.

URI Reference

Within this specification, the term URI Reference, unless otherwise stated, refers to a string in the lexical space of the xs:anyURI datatype as defined in [XML Schema Part 2].

use

If a package Q contains an xsl:use-package element that references package P, then package Q is said to use package P. In this relationship package Q is referred to as the using package, package P as the used package.

user-defined data element

In addition to declarations, the xsl:stylesheet element may contain among its children any element not from the XSLT namespace, provided that the expanded QName of the element has a non-null namespace URI. Such elements are referred to as user-defined data elements.

value

A variable is a binding between a name and a value. The value of a variable is any sequence (of nodes, atomic values, and/or function items), as defined in [Data Model].

value template

Collectively, attribute value templates and text value templates are referred to as value templates.

variable

The xsl:variable element declares a variable, which may be a global variable or a local variable.

variable-binding element

The two elements xsl:variable and xsl:param are referred to as variable-binding elements

visibility

The visibility of a component is one of: private, public, abstract, final, or hidden.

whitespace text node

A whitespace text node is a text node whose content consists entirely of whitespace characters (that is, #x09, #x0A, #x0D, or #x20).

XML namespace

The XML namespace, defined in [Namespaces in XML] as http://www.w3.org/XML/1998/namespace, is used for attributes such as xml:lang, xml:space, and xml:id.

XPath 1.0 compatibility mode

The term XPath 1.0 compatibility mode is defined in Section 2.1.1 Static Context XP30. This is a setting in the static context of an XPath expression; it has two values, true and false. When the value is set to true, the semantics of function calls and certain other operations are adjusted to give a greater degree of backwards compatibility between XPath 3.0 and XPath 1.0.

XQuery Invocation Feature

A processor that claims conformance with the XQuery invocation feature must allow XQuery library modules to be referenced in xsl:use-package, and must allow the using package to reference the public functions and variables declared in the referenced library module.

XSLT 1.0 behavior

An element in the stylesheet is processed with XSLT 1.0 behavior if its effective version is equal to 1.0.

XSLT 1.0 compatibility feature

A processor that claims conformance with the XSLT 1.0 compatibility feature must support the processing of stylesheet instructions and XPath expressions with XSLT 1.0 behavior, as defined in 3.10 Backwards Compatible Processing.

XSLT 2.0 behavior

An element is processed with XSLT 2.0 behavior if its effective version is equal to 2.0.

XSLT element

An XSLT element is an element in the XSLT namespace whose syntax and semantics are defined in this specification.

XSLT instruction

An XSLT instruction is an XSLT element whose syntax summary in this specification contains the annotation <!-- category: instruction -->.

XSLT namespace

The XSLT namespace has the URI http://www.w3.org/1999/XSL/Transform. It is used to identify elements, attributes, and other names that have a special meaning defined in this specification.

D Element Syntax Summary (Non-Normative)

The syntax of each XSLT element is summarized below, together with the context in the stylesheet where the element may appear. Some elements (specifically, instructions) are allowed as a child of any element that is allowed to contain a sequence constructor. These elements are:

xsl:accept

 

Model:

<xsl:accept
  component = "template" | "function" | "accumulator" | "attribute-set" | "variable" | "mode"
  names = tokens
  visibility = "public" | "private" | "final" | "abstract" | "hidden" | "absent" />

Permitted parent elements:

xsl:accumulator

 

Category: declaration

Model:

<xsl:accumulator
  name = eqname
  initial-value = expression
  as? = sequence-type
  visibility? = "public" | "private" | "final" | "abstract"
  streamable? = "yes" | "no" >
  <!-- Content: xsl:accumulator-rule+ -->
</xsl:accumulator>

Permitted parent elements:

xsl:accumulator-rule

 

Model:

<xsl:accumulator-rule
  match = pattern
  phase? = "start" | "end"
  new-value = expression />

Permitted parent elements:

xsl:analyze-string

 

Category: instruction

Model:

<xsl:analyze-string
  select = expression
  regex = { string }
  flags? = { string } >
  <!-- Content: (xsl:matching-substring?, xsl:non-matching-substring?, xsl:fallback*) -->
</xsl:analyze-string>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:apply-imports

 

Category: instruction

Model:

<xsl:apply-imports>
  <!-- Content: xsl:with-param* -->
</xsl:apply-imports>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:apply-templates

 

Category: instruction

Model:

<xsl:apply-templates
  select? = expression
  mode? = token >
  <!-- Content: (xsl:sort | xsl:with-param)* -->
</xsl:apply-templates>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:assert

 

Category: instruction

Model:

<xsl:assert
  test = expression
  select? = expression
  error-code? = { eqname } >
  <!-- Content: sequence-constructor -->
</xsl:assert>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:attribute

 

Category: instruction

Model:

<xsl:attribute
  name = { qname }
  namespace? = { uri }
  select? = expression
  separator? = { string }
  type? = eqname
  validation? = "strict" | "lax" | "preserve" | "strip"
  on-empty? = expression >
  <!-- Content: sequence-constructor -->
</xsl:attribute>

Permitted parent elements:

  • xsl:attribute-set
  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:attribute-set

 

Category: declaration

Model:

<xsl:attribute-set
  name = eqname
  use-attribute-sets? = eqnames
  visibility? = "public" | "private" | "final" | "abstract"
  streamable? = "yes" | "no" >
  <!-- Content: xsl:attribute* -->
</xsl:attribute-set>

Permitted parent elements:

xsl:break

 

Category: instruction

Model:

<xsl:break
  select? = expression >
  <!-- Content: (sequence-constructor) -->
</xsl:break>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:call-template

 

Category: instruction

Model:

<xsl:call-template
  name = eqname >
  <!-- Content: xsl:with-param* -->
</xsl:call-template>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:catch

 

Model:

<xsl:catch
  errors? = tokens
  select? = expression >
  <!-- Content: sequence-constructor -->
</xsl:catch>

Permitted parent elements:

xsl:character-map

 

Category: declaration

Model:

<xsl:character-map
  name = eqname
  use-character-maps? = eqnames >
  <!-- Content: (xsl:output-character*) -->
</xsl:character-map>

Permitted parent elements:

xsl:choose

 

Category: instruction

Model:

<xsl:choose>
  <!-- Content: (xsl:when+, xsl:otherwise?) -->
</xsl:choose>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:comment

 

Category: instruction

Model:

<xsl:comment
  select? = expression >
  <!-- Content: sequence-constructor -->
</xsl:comment>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:context-item

 

Model:

<xsl:context-item
  as? = sequence-type
  use? = "required" | "optional" | "prohibited" />

Permitted parent elements:

xsl:copy

 

Category: instruction

Model:

<xsl:copy
  select? = expression
  copy-namespaces? = "yes" | "no"
  inherit-namespaces? = "yes" | "no"
  use-attribute-sets? = eqnames
  type? = eqname
  validation? = "strict" | "lax" | "preserve" | "strip"
  on-empty? = expression >
  <!-- Content: sequence-constructor -->
</xsl:copy>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:copy-of

 

Category: instruction

Model:

<xsl:copy-of
  select = expression
  copy-namespaces? = "yes" | "no"
  type? = eqname
  validation? = "strict" | "lax" | "preserve" | "strip" />

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:decimal-format

 

Category: declaration

Model:

<xsl:decimal-format
  name? = eqname
  decimal-separator? = char
  grouping-separator? = char
  infinity? = string
  minus-sign? = char
  NaN? = string
  percent? = char
  per-mille? = char
  zero-digit? = char
  digit? = char
  pattern-separator? = char />

Permitted parent elements:

xsl:document

 

Category: instruction

Model:

<xsl:document
  validation? = "strict" | "lax" | "preserve" | "strip"
  type? = eqname >
  <!-- Content: sequence-constructor -->
</xsl:document>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:element

 

Category: instruction

Model:

<xsl:element
  name = { qname }
  namespace? = { uri }
  inherit-namespaces? = "yes" | "no"
  use-attribute-sets? = eqnames
  type? = eqname
  validation? = "strict" | "lax" | "preserve" | "strip"
  on-empty? = expression >
  <!-- Content: sequence-constructor -->
</xsl:element>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:evaluate

 

Category: instruction

Model:

<xsl:evaluate
  xpath = expression
  as? = sequence-type
  base-uri? = { uri }
  with-params? = expression
  context-item? = expression
  namespace-context? = expression
  schema-aware? = { "yes" | "no" } >
  <!-- Content: (xsl:with-param | xsl:fallback)* -->
</xsl:evaluate>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:expose

 

Model:

<xsl:expose
  component = "template" | "function" | "accumulator" | "attribute-set" | "variable" | "mode"
  names = tokens
  visibility = "public" | "private" | "final" | "abstract" />

Permitted parent elements:

xsl:fallback

 

Category: instruction

Model:

<xsl:fallback>
  <!-- Content: sequence-constructor -->
</xsl:fallback>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:for-each

 

Category: instruction

Model:

<xsl:for-each
  select = expression >
  <!-- Content: (xsl:sort*, sequence-constructor) -->
</xsl:for-each>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:for-each-group

 

Category: instruction

Model:

<xsl:for-each-group
  select = expression
  group-by? = expression
  group-adjacent? = expression
  group-starting-with? = pattern
  group-ending-with? = pattern
  bind-group? = eqname
  bind-grouping-key? = eqname
  composite? = "yes" | "no"
  collation? = { uri } >
  <!-- Content: (xsl:sort*, sequence-constructor) -->
</xsl:for-each-group>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:fork

 

Category: instruction

Model:

<xsl:fork>
  <!-- Content: ((xsl:sequence | xsl:fallback))+ -->
</xsl:fork>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:function

 

Category: declaration

Model:

<xsl:function
  name = eqname
  as? = sequence-type
  visibility? = "public" | "private" | "final" | "abstract"
  override-extension-function? = "yes" | "no"
  [override]? = "yes" | "no"
  identity-sensitive? = "yes" | "no"
  cache? = "full" | "partial" | "no" >
  <!-- Content: (xsl:param*, sequence-constructor) -->
</xsl:function>

Permitted parent elements:

xsl:if

 

Category: instruction

Model:

<xsl:if
  test = expression >
  <!-- Content: sequence-constructor -->
</xsl:if>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:import

 

Category: declaration

Model:

<xsl:import
  href = uri />

Permitted parent elements:

xsl:import-schema

 

Category: declaration

Model:

<xsl:import-schema
  namespace? = uri
  schema-location? = uri >
  <!-- Content: xs:schema? -->
</xsl:import-schema>

Permitted parent elements:

xsl:include

 

Category: declaration

Model:

<xsl:include
  href = uri />

Permitted parent elements:

xsl:iterate

 

Category: instruction

Model:

<xsl:iterate
  select = expression >
  <!-- Content: (xsl:param*, sequence-constructor, xsl:on-completion?) -->
</xsl:iterate>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:key

 

Category: declaration

Model:

<xsl:key
  name = eqname
  match = pattern
  use? = expression
  composite? = "yes" | "no"
  collation? = uri >
  <!-- Content: sequence-constructor -->
</xsl:key>

Permitted parent elements:

xsl:map

 

Category: instruction

Model:

<xsl:map>
  <!-- Content: sequence-constructor -->
</xsl:map>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:map-entry

 

Category: instruction

Model:

<xsl:map-entry
  key = expression
  select? = expression >
  <!-- Content: sequence-constructor -->
</xsl:map-entry>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:matching-substring

 

Model:

<xsl:matching-substring>
  <!-- Content: sequence-constructor -->
</xsl:matching-substring>

Permitted parent elements:

xsl:merge

 

Category: instruction

Model:

<xsl:merge
  bind-group? = eqname
  bind-key? = eqname >
  <!-- Content: (xsl:merge-source+, xsl:merge-action, xsl:fallback*) -->
</xsl:merge>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:merge-action

 

Model:

<xsl:merge-action>
  <!-- Content: (sequence-constructor) -->
</xsl:merge-action>

Permitted parent elements:

xsl:merge-key

 

Model:

<xsl:merge-key
  select? = expression
  lang? = { language }
  order? = { "ascending" | "descending" }
  collation? = { uri }
  case-order? = { "upper-first" | "lower-first" }
  data-type? = { "text" | "number" | eqname } >
  <!-- Content: sequence-constructor -->
</xsl:merge-key>

Permitted parent elements:

xsl:merge-source

 

Model:

<xsl:merge-source
  for-each? = expression
  select = expression
  bind-source? = eqname
  streamable? = "yes" | "no"
  sort-before-merge? = "yes" | "no" >
  <!-- Content: xsl:merge-key+ -->
</xsl:merge-source>

Permitted parent elements:

xsl:message

 

Category: instruction

Model:

<xsl:message
  select? = expression
  terminate? = { "yes" | "no" }
  error-code? = { eqname } >
  <!-- Content: sequence-constructor -->
</xsl:message>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:mode

 

Category: declaration

Model:

<xsl:mode
  name? = eqname
  streamable? = "yes" | "no"
  on-no-match? = "deep-copy" | "shallow-copy" | "deep-skip" | "shallow-skip" | "text-only-copy" | "fail"
  on-multiple-match? = "use-last" | "fail"
  warning-on-no-match? = "yes" | "no"
  warning-on-multiple-match? = "yes" | "no"
  typed? = "yes" | "no" | "strict" | "lax" | "unspecified"
  visibility? = "public" | "private" | "final" >
  <!-- Content: (xsl:context-item?) -->
</xsl:mode>

Permitted parent elements:

xsl:namespace

 

Category: instruction

Model:

<xsl:namespace
  name = { ncname }
  select? = expression >
  <!-- Content: sequence-constructor -->
</xsl:namespace>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:namespace-alias

 

Category: declaration

Model:

<xsl:namespace-alias
  stylesheet-prefix = prefix | "#default"
  result-prefix = prefix | "#default" />

Permitted parent elements:

xsl:next-iteration

 

Category: instruction

Model:

<xsl:next-iteration>
  <!-- Content: (xsl:with-param*) -->
</xsl:next-iteration>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:next-match

 

Category: instruction

Model:

<xsl:next-match>
  <!-- Content: (xsl:with-param | xsl:fallback)* -->
</xsl:next-match>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:non-matching-substring

 

Model:

<xsl:non-matching-substring>
  <!-- Content: sequence-constructor -->
</xsl:non-matching-substring>

Permitted parent elements:

xsl:number

 

Category: instruction

Model:

<xsl:number
  value? = expression
  select? = expression
  level? = "single" | "multiple" | "any"
  count? = pattern
  from? = pattern
  format? = { string }
  lang? = { language }
  letter-value? = { "alphabetic" | "traditional" }
  ordinal? = { string }
  start-at? = { integer }
  grouping-separator? = { char }
  grouping-size? = { integer } />

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:on-completion

 

Model:

<xsl:on-completion
  select? = expression >
  <!-- Content: (sequence-constructor) -->
</xsl:on-completion>

Permitted parent elements:

xsl:otherwise

 

Model:

<xsl:otherwise>
  <!-- Content: sequence-constructor -->
</xsl:otherwise>

Permitted parent elements:

xsl:output

 

Category: declaration

Model:

<xsl:output
  name? = eqname
  method? = "xml" | "html" | "xhtml" | "text" | eqname
  byte-order-mark? = "yes" | "no"
  cdata-section-elements? = eqnames
  doctype-public? = string
  doctype-system? = string
  encoding? = string
  escape-uri-attributes? = "yes" | "no"
  html-version? = decimal
  include-content-type? = "yes" | "no"
  indent? = "yes" | "no"
  item-separator? = string
  media-type? = string
  normalization-form? = "NFC" | "NFD" | "NFKC" | "NFKD" | "fully-normalized" | "none" | nmtoken
  omit-xml-declaration? = "yes" | "no"
  parameter-document? = uri
  standalone? = "yes" | "no" | "omit"
  suppress-indentation? = eqnames
  undeclare-prefixes? = "yes" | "no"
  use-character-maps? = eqnames
  version? = nmtoken />

Permitted parent elements:

xsl:output-character

 

Model:

<xsl:output-character
  character = char
  string = string />

Permitted parent elements:

xsl:override

 

Model:

<xsl:override>
  <!-- Content: (xsl:template | xsl:function | xsl:accumulator | xsl:variable | xsl:param | xsl:attribute-set)* -->
</xsl:override>

Permitted parent elements:

xsl:package

 

Model:

<xsl:package
  name? = uri
  package-version? = string
  version = decimal
  input-type-annotations? = "preserve" | "strip" | "unspecified"
  default-mode? = eqname | "#unnamed"
  default-validation? = "preserve" | "strip"
  default-collation? = uris
  extension-element-prefixes? = prefixes
  exclude-result-prefixes? = prefixes
  expand-text? = "yes" | "no"
  use-when? = expression
  xpath-default-namespace? = uri >
  <!-- Content: (xsl:use-package*, (xsl:stylesheet | xsl:transform), xsl:expose*) -->
</xsl:package>

Permitted parent elements:

  • None

xsl:param

 

Category: declaration

Model:

<xsl:param
  name = eqname
  select? = expression
  as? = sequence-type
  required? = "yes" | "no"
  tunnel? = "yes" | "no"
  static? = "yes" | "no"
  visibility? = "public" | "private" | "final" | "abstract" >
  <!-- Content: sequence-constructor -->
</xsl:param>

Permitted parent elements:

xsl:perform-sort

 

Category: instruction

Model:

<xsl:perform-sort
  select? = expression >
  <!-- Content: (xsl:sort+, sequence-constructor) -->
</xsl:perform-sort>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:preserve-space

 

Category: declaration

Model:

<xsl:preserve-space
  elements = tokens />

Permitted parent elements:

xsl:processing-instruction

 

Category: instruction

Model:

<xsl:processing-instruction
  name = { ncname }
  select? = expression >
  <!-- Content: sequence-constructor -->
</xsl:processing-instruction>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:result-document

 

Category: instruction

Model:

<xsl:result-document
  format? = { eqname }
  href? = { uri }
  validation? = "strict" | "lax" | "preserve" | "strip"
  type? = eqname
  method? = { "xml" | "html" | "xhtml" | "text" | eqname }
  byte-order-mark? = { "yes" | "no" }
  cdata-section-elements? = { eqnames }
  doctype-public? = { string }
  doctype-system? = { string }
  encoding? = { string }
  escape-uri-attributes? = { "yes" | "no" }
  html-version? = { decimal }
  include-content-type? = { "yes" | "no" }
  indent? = { "yes" | "no" }
  item-separator? = { string }
  media-type? = { string }
  normalization-form? = { "NFC" | "NFD" | "NFKC" | "NFKD" | "fully-normalized" | "none" | nmtoken }
  omit-xml-declaration? = { "yes" | "no" }
  parameter-document? = { uri }
  standalone? = { "yes" | "no" | "omit" }
  suppress-indentation? = { eqnames }
  undeclare-prefixes? = { "yes" | "no" }
  use-character-maps? = eqnames
  output-version? = { nmtoken } >
  <!-- Content: sequence-constructor -->
</xsl:result-document>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:sequence

 

Category: instruction

Model:

<xsl:sequence
  select? = expression >
  <!-- Content: sequence-constructor -->
</xsl:sequence>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:sort

 

Model:

<xsl:sort
  select? = expression
  lang? = { language }
  order? = { "ascending" | "descending" }
  collation? = { uri }
  stable? = { "yes" | "no" }
  case-order? = { "upper-first" | "lower-first" }
  data-type? = { "text" | "number" | eqname } >
  <!-- Content: sequence-constructor -->
</xsl:sort>

Permitted parent elements:

xsl:stream

 

Category: instruction

Model:

<xsl:stream
  href = { uri }
  validation? = "strict" | "lax" | "preserve" | "strip"
  type? = eqname >
  <!-- Content: sequence-constructor -->
</xsl:stream>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:strip-space

 

Category: declaration

Model:

<xsl:strip-space
  elements = tokens />

Permitted parent elements:

xsl:stylesheet

 

Model:

<xsl:stylesheet
  id? = id
  version? = decimal
  default-mode? = eqname | "#unnamed"
  default-validation? = "preserve" | "strip"
  input-type-annotations? = "preserve" | "strip" | "unspecified"
  default-collation? = uris
  extension-element-prefixes? = prefixes
  exclude-result-prefixes? = prefixes
  expand-text? = "yes" | "no"
  use-when? = expression
  xpath-default-namespace? = uri >
  <!-- Content: (xsl:use-package*, other-declarations) -->
</xsl:stylesheet>

Permitted parent elements:

  • None

xsl:template

 

Category: declaration

Model:

<xsl:template
  match? = pattern
  name? = eqname
  priority? = decimal
  mode? = tokens
  as? = sequence-type
  visibility? = "public" | "private" | "final" | "abstract" >
  <!-- Content: (xsl:context-item?, xsl:param*, sequence-constructor) -->
</xsl:template>

Permitted parent elements:

xsl:text

 

Category: instruction

Model:

<xsl:text
  [disable-output-escaping]? = "yes" | "no" >
  <!-- Content: #PCDATA -->
</xsl:text>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:transform

 

Model:

<xsl:transform
  id? = id
  version? = decimal
  default-mode? = eqname | "#unnamed"
  default-validation? = "preserve" | "strip"
  input-type-annotations? = "preserve" | "strip" | "unspecified"
  default-collation? = uris
  extension-element-prefixes? = prefixes
  exclude-result-prefixes? = prefixes
  expand-text? = "yes" | "no"
  use-when? = expression
  xpath-default-namespace? = uri >
  <!-- Content: (xsl:use-package*, other-declarations) -->
</xsl:transform>

Permitted parent elements:

  • None

xsl:try

 

Category: instruction

Model:

<xsl:try
  select? = expression >
  <!-- Content: (sequence-constructor, xsl:catch, (xsl:catch | xsl:fallback)*) -->
</xsl:try>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:use-package

 

Model:

<xsl:use-package
  name = uri
  package-version? = token >
  <!-- Content: (xsl:accept | xsl:override)* -->
</xsl:use-package>

Permitted parent elements:

xsl:value-of

 

Category: instruction

Model:

<xsl:value-of
  select? = expression
  separator? = { string }
  [disable-output-escaping]? = "yes" | "no" >
  <!-- Content: sequence-constructor -->
</xsl:value-of>

Permitted parent elements:

  • any XSLT element whose content model is sequence constructor
  • any literal result element

xsl:variable

 

Category: declaration instruction

Model:

<xsl:variable
  name = eqname
  select? = expression
  as? = sequence-type
  static? = "yes" | "no"
  visibility? = "public" | "private" | "final" | "abstract" >
  <!-- Content: sequence-constructor -->
</xsl:variable>

Permitted parent elements:

xsl:when

 

Model:

<xsl:when
  test = expression >
  <!-- Content: sequence-constructor -->
</xsl:when>

Permitted parent elements:

xsl:with-param

 

Model:

<xsl:with-param
  name = eqname
  select? = expression
  as? = sequence-type
  tunnel? = "yes" | "no" >
  <!-- Content: sequence-constructor -->
</xsl:with-param>

Permitted parent elements:

E Summary of Error Conditions (Non-Normative)

This appendix provides a summary of error conditions that a processor may signal. This list includes all error codes defined in this specification, but this is not an exhaustive list of all errors that can occur. Implementations must signal errors using these error codes, and applications can test for these codes; however, when more than one rule in the specification is violated, different processors will not necessarily signal the same error code. Implementations are not required to signal errors using the descriptive text used here.

Note:

The appendix is non-normative because the same information is given normatively elsewhere.

Static errors

ERR XTSE0010

It is a static error if an XSLT-defined element is used in a context where it is not permitted, if a required attribute is omitted, or if the content of the element does not correspond to the content that is allowed for the element.

ERR XTSE0020

It is a static error if an attribute (other than an attribute written using curly brackets in a position where an attribute value template is permitted) contains a value that is not one of the permitted values for that attribute.

ERR XTSE0080

It is a static error to use a reserved namespace in the name of a named template, a mode, an attribute set, a key, a decimal-format, a variable or parameter, a stylesheet function, a named output definition, or a character map.

ERR XTSE0090

It is a static error for an element from the XSLT namespace to have an attribute whose namespace is either null (that is, an attribute with an unprefixed name) or the XSLT namespace, other than attributes defined for the element in this document.

ERR XTSE0110

The value of the version attribute if present must be a number: specifically, it must be a valid instance of the type xs:decimal as defined in [XML Schema Part 2].

ERR XTSE0120

An xsl:stylesheet element must not have any text node children.

ERR XTSE0125

It is a static error if the value of an [xsl:]default-collation attribute, after resolving against the base URI, contains no URI that the implementation recognizes as a collation URI.

ERR XTSE0130

It is a static error if the xsl:stylesheet element has a child element whose name has a null namespace URI.

ERR XTSE0150

A literal result element that is used as the outermost element of a simplified stylesheet module must have an xsl:version attribute.

ERR XTSE0165

It is a static error if the processor is not able to retrieve the resource identified by the URI reference [ in the href attribute of xsl:include or xsl:import ] , or if the resource that is retrieved does not contain a stylesheet module.

ERR XTSE0170

An xsl:include element must be a top-level element.

ERR XTSE0180

It is a static error if a stylesheet module directly or indirectly includes itself.

ERR XTSE0190

An xsl:import element must be a top-level element.

ERR XTSE0210

It is a static error if a stylesheet module directly or indirectly imports itself.

ERR XTSE0215

It is a static error if an xsl:import-schema element that contains an xs:schema element has a schema-location attribute, or if it has a namespace attribute that conflicts with the target namespace of the contained schema.

ERR XTSE0220

It is a static error if the synthetic schema document does not satisfy the constraints described in [XML Schema Part 1] (section 5.1, Errors in Schema Construction and Structure). This includes, without loss of generality, conflicts such as multiple definitions of the same name.

ERR XTSE0260

Within an XSLT element that is required to be empty, any content other than comments or processing instructions, including any whitespace text node preserved using the xml:space="preserve" attribute, is a static error.

ERR XTSE0265

It is a static error if there is a stylesheet module in a package that specifies input-type-annotations="strip" and another stylesheet module that specifies input-type-annotations="preserve", or if a stylesheet module specifies the value strip or preserve and the same value is not specified on the xsl:package element of the containing package.

ERR XTSE0270

It is a static error if within any package the same NameTestXP30 appears in both an xsl:strip-space and an xsl:preserve-space declaration if both have the same import precedence. Two NameTests are considered the same if they match the same set of names (which can be determined by comparing them after expanding namespace prefixes to URIs).

ERR XTSE0280

In the case of a prefixed lexical QName used as the value (or as part of the value) of an attribute in the stylesheet, or appearing within an XPath expression in the stylesheet, it is a static error if the defining element has no namespace node whose name matches the prefix of the lexical QName.

ERR XTSE0340

Where an attribute is defined to contain a pattern, it is a static error if the pattern does not match the production Pattern30.

ERR XTSE0350

It is a static error if an unescaped left curly bracket appears in a fixed part of a value template without a matching right curly bracket.

ERR XTSE0370

It is a static error if an unescaped right curly bracket occurs in a fixed part of a value template.

ERR XTSE0500

An xsl:template element must have either a match attribute or a name attribute, or both. An xsl:template element that has no match attribute must have no mode attribute and no priority attribute. An xsl:template element that has no name attribute must have no visibility attribute.

ERR XTSE0530

The value of the priority attribute [ of the xsl:template element] must conform to the rules for the xs:decimal type defined in [XML Schema Part 2]. Negative values are permitted.

ERR XTSE0542

It is a static error if an xsl:mode declaration specifying initial="no" contains an xsl:context-item element.

ERR XTSE0545

It is a static error if a named or unnamed mode contains two conflicting values for the same attribute in different xsl:mode declarations having the same import precedence, unless there is another definition of the same attribute with higher import precedence. The attributes in question are the attributes other than name on the xsl:mode element, and the as attribute on the contained xsl:context-item element if present.

ERR XTSE0548

It is a static error if there is both (a) a mode definition in the stylesheet that has the effective attribute values streamable="yes" and initial="yes", and (b) a global variable in the stylesheet whose initializing expression is not motionless with respect to its context item, as defined in 19 Streamability.

ERR XTSE0550

It is a static error if the list of modes [in the mode attribute of xsl:template ] is empty, if the same token is included more than once in the list, if the list contains an invalid token, or if the token #all appears together with any other value.

ERR XTSE0580

It is a static error if the values of the name attribute of two sibling xsl:param elements represent the same expanded QName.

ERR XTSE0620

It is a static error if a variable-binding element has a select attribute and has non-empty content.

ERR XTSE0630

It is a static error if a stylesheet contains more than one non-hidden binding of a global variable with the same name and same import precedence, unless it also contains another binding with the same name and higher import precedence.

ERR XTSE0650

It is a static error if a stylesheet contains an xsl:call-template instruction whose name attribute does not match the name attribute of any named template visible in the containing package (this includes any template defined in this package, as well as templates accepted from used packages whose visibility in this package is not hidden). For more details of the process of binding the called template, see 3.6.2.6 Binding References to Components.

ERR XTSE0660

It is a static error if a package contains more than one non-hidden template with the same name and the same import precedence, unless it also contains a template with the same name and higher import precedence.

ERR XTSE0670

It is a static error if two or more sibling xsl:with-param elements have name attributes that represent the same expanded QName.

ERR XTSE0680

In the case of xsl:call-template, it is a static error to pass a non-tunnel parameter named x to a template that does not have a non-tunnel template parameter named x, unless the xsl:call-template instruction is processed with XSLT 1.0 behavior.

ERR XTSE0690

It is a static error if a template that is invoked using xsl:call-template declares a template parameter specifying required="yes" and not specifying tunnel="yes", if no value for this parameter is supplied by the calling xsl:call-template instruction.

ERR XTSE0710

It is a static error if the value of the use-attribute-sets attribute of an xsl:copy, xsl:element, or xsl:attribute-set element, or the xsl:use-attribute-sets attribute of a literal result element, is not a whitespace-separated sequence of EQNames, or if it contains a QName that does not match the name attribute of any xsl:attribute-set declaration in the stylesheet.

ERR XTSE0720

It is a static error if an xsl:attribute-set element directly or indirectly references itself via the names contained in the use-attribute-sets attribute.

ERR XTSE0740

It is a static error if a stylesheet function has a name that is in no namespace.

ERR XTSE0760

Because arguments to a stylesheet function call must all be specified, the xsl:param elements within an xsl:function element must not specify a default value: this means they must be empty, and must not have a select attribute.

ERR XTSE0770

It is a static error for a package to contain two or more non-hidden functions with the same expanded QName, the same arity, and the same import precedence, unless there is another function with the same expanded QName and arity, and a higher import precedence.

ERR XTSE0805

It is a static error if an attribute on a literal result element is in the XSLT namespace, unless it is one of the attributes explicitly defined in this specification.

ERR XTSE0808

It is a static error if a namespace prefix is used within the [xsl:]exclude-result-prefixes attribute and there is no namespace binding in scope for that prefix.

ERR XTSE0809

It is a static error if the value #default is used within the [xsl:]exclude-result-prefixes attribute and the parent element of the [xsl:]exclude-result-prefixes attribute has no default namespace.

ERR XTSE0810

It is a static error if within a package there is more than one such declaration [more than one xsl:namespace-alias declaration] with the same literal namespace URI and the same import precedence and different values for the target namespace URI, unless there is also an xsl:namespace-alias declaration with the same literal namespace URI and a higher import precedence.

ERR XTSE0812

It is a static error if a value other than #default is specified for either the stylesheet-prefix or the result-prefix attributes of the xsl:namespace-alias element when there is no in-scope binding for that namespace prefix.

ERR XTSE0840

It is a static error if the select attribute of the xsl:attribute element is present unless the element has empty content.

ERR XTSE0870

It is a static error if the select attribute of the xsl:value-of element is present when the content of the element is non-empty

ERR XTSE0880

It is a static error if the select attribute of the xsl:processing-instruction element is present unless the element has empty content.

ERR XTSE0910

It is a static error if the select attribute of the xsl:namespace element is present when the element has content other than one or more xsl:fallback instructions, or if the select attribute is absent when the element has empty content.

ERR XTSE0940

It is a static error if the select attribute of the xsl:comment element is present unless the element has empty content.

ERR XTSE0975

It is a static error if the value attribute of xsl:number is present unless the select, level, count, and from attributes are all absent.

ERR XTSE1015

It is a static error if an xsl:sort element with a select attribute has non-empty content.

ERR XTSE1017

It is a static error if an xsl:sort element other than the first in a sequence of sibling xsl:sort elements has a stable attribute.

ERR XTSE1040

It is a static error if an xsl:perform-sort instruction with a select attribute has any content other than xsl:sort and xsl:fallback instructions.

ERR XTSE1060

It is a static error if the current-group function is used within a pattern.

ERR XTSE1070

It is a static error if the current-grouping-key function is used within a pattern.

ERR XTSE1080

These four attributes [the group-by, group-adjacent, group-starting-with, and group-ending-with attributes of xsl:for-each-group ] are mutually exclusive: it is a static error if none of these four attributes is present or if more than one of them is present.

ERR XTSE1090

It is a static error to specify the collation attribute or the composite attribute if neither the group-by attribute nor group-adjacent attribute is specified.

ERR XTSE1130

It is a static error if the xsl:analyze-string instruction contains neither an xsl:matching-substring nor an xsl:non-matching-substring element.

ERR XTSE1205

It is a static error if an xsl:key declaration has a use attribute and has non-empty content, or if it has empty content and no use attribute.

ERR XTSE1210

It is a static error if the xsl:key declaration has a collation attribute whose value (after resolving against the base URI) is not a URI recognized by the implementation as referring to a collation.

ERR XTSE1220

It is a static error if there are several xsl:key declarations in the same package with the same key name and different effective collations. Two collations are the same if their URIs are equal under the rules for comparing xs:anyURI values, or if the implementation can determine that they are different URIs referring to the same collation.

ERR XTSE1222

It is a static error if there are several xsl:key declarations in the stylesheet with the same key name and different effective values for the composite attribute.

ERR XTSE1290

It is a static error if a named or unnamed decimal format contains two conflicting values for the same attribute in different xsl:decimal-format declarations having the same import precedence, unless there is another definition of the same attribute with higher import precedence.

ERR XTSE1295

It is a static error if the character specified in the zero-digit attribute is not a digit or is a digit that does not have the numeric value zero.

ERR XTSE1300

It is a static error if, for any named or unnamed decimal format, the variables representing characters used in a picture string do not each have distinct values. These variables are decimal-separator-sign, grouping-sign, percent-sign, per-mille-sign, digit-zero-sign, digit-sign, and pattern-separator-sign.

ERR XTSE1430

It is a static error if there is no namespace bound to the prefix on the element bearing the [xsl:]extension-element-prefixes attribute or, when #default is specified, if there is no default namespace.

ERR XTSE1505

It is a static error if both the [xsl:]type and [xsl:]validation attributes are present on the xsl:element, xsl:attribute, xsl:copy, xsl:copy-of, xsl:document, or xsl:result-document instructions, or on a literal result element.

ERR XTSE1520

It is a static error if the value of the type attribute of an xsl:element, xsl:attribute, xsl:copy, xsl:copy-of, xsl:document, or xsl:result-document instruction, or the xsl:type attribute of a literal result element, is not a valid QName, or if it uses a prefix that is not defined in an in-scope namespace declaration, or if the QName is not the name of a type definition included in the in-scope schema components for the stylesheet.

ERR XTSE1530

It is a static error if the value of the type attribute of an xsl:attribute instruction refers to a complex type definition

ERR XTSE1560

It is a static error if two xsl:output declarations within an output definition specify explicit values for the same attribute (other than cdata-section-elements and use-character-maps), with the values of the attributes being not equal, unless there is another xsl:output declaration within the same output definition that has higher import precedence and that specifies an explicit value for the same attribute.

ERR XTSE1570

The value [of the method attribute on xsl:output ] must (if present) be a valid EQName. If it is a lexical QName with no a prefix, then it identifies a method specified in [XSLT and XQuery Serialization] and must be one of xml, html, xhtml, or text.

ERR XTSE1580

It is a static error if the stylesheet contains two or more character maps with the same name and the same import precedence, unless it also contains another character map with the same name and higher import precedence.

ERR XTSE1590

It is a static error if a name in the use-character-maps attribute of the xsl:output or xsl:character-map elements does not match the name attribute of any xsl:character-map in the stylesheet.

ERR XTSE1600

It is a static error if a character map references itself, directly or indirectly, via a name in the use-character-maps attribute.

ERR XTSE1650

A non-schema-aware processor must signal a static error if the stylesheet includes an xsl:import-schema declaration.

ERR XTSE1660

A non-schema-aware processor must signal a static error if the stylesheet includes an [xsl:]type attribute, or an [xsl:]validation or [xsl:]default-validation attribute with a value other than strip, preserve, or lax.

ERR XTSE2200

It is a static error if the number of xsl:merge-key children of a xsl:merge-source element is not equal to the number of xsl:merge-key children of another xsl:merge-source child of the same xsl:merge instruction.

ERR XTSE3010

It is a static error if the exposed visibility of a component is inconsistent with its potential visibility, as defined in the above table, unless the token that matches the component is a wildcard, in which case it is treated as not matching that component.

ERR XTSE3020

It is a static error if an xsl:expose element matches no components in the containing package, unless the tokens in the names attribute are all wildcards.

ERR XTSE3030

It is a static error if an xsl:accept element matches no components in the used package, unless the tokens in its names attribute are all wildcards.

ERR XTSE3040

It is a static error if the visibility assigned to a component by an xsl:accept element is incompatible with the visibility of the corresponding component in the used package, as defined by the above table, unless the token that matches the component name is a wildcard, in which case the xsl:accept element is treated as not matching that component.

ERR XTSE3050

It is a static error if the xsl:use-package elements in a package manifest cause two or more homonymous components to be accepted with a visibility other than hidden.

ERR XTDE3052

It is a dynamic error if an invocation of an absent component (that is, an abstract component accepted into a using package with visibility="absent") is evaluated.

ERR XTSE3055

It is a static error if a component declaration appearing as a child of xsl:override is homonymous with any other declaration in the using package, regardless of import precedence, including any other overriding declaration in the package manifest of the using package.

ERR XTSE3058

It is a static error if a component declaration appearing as a child of xsl:override does not match (is not homonymous with) some component in the used package.

ERR XTSE3060

It is a static error if the component referenced by an xsl:override declaration has visibility other than public or abstract

ERR XTSE3070

It is a static error if the signature of an overriding component is not compatible with the signature of the component that it is overriding.

ERR XTSE3080

It is a static error if a top-level package intended for execution (as distinct from a library package) contains symbolic references referring to components whose visibility is abstract.

ERR XTSE3120

It is a static error if an xsl:break or xsl:next-iteration element appears other than in a tail position within the sequence constructor forming the body of an xsl:iterate instruction.

ERR XTSE3125

It is a static error if the select attribute of xsl:break or xsl:on-completion is present and the instruction has children.

ERR XTSE3130

It is a static error if the name attribute of an xsl:with-param child of an xsl:next-iteration element does not match the name attribute of an xsl:param child of the innermost containing xsl:iterate instruction.

ERR XTSE3140

It is a static error if the select attribute of the xsl:try element is present and the element has children other than xsl:catch and xsl:fallback elements.

ERR XTSE3150

It is a static error if the select attribute of the xsl:catch element is present unless the element has empty content.

ERR XTSE3185

It is a static error if the select attribute of xsl:sequence is present and the instruction has children other than xsl:fallback.

ERR XTSE3190

It is a static error if two sibling xsl:merge-source elements have the same name, whether explicit or implicit.

ERR XTSE3200

It is a static error if an xsl:merge-key element with a select attribute has non-empty content.

ERR XTSE3220

It is a static error if a variable bound in the bind-group or bind-grouping-key attribute of an xsl:for-each-group instruction is referenced within an expression in the lang, order, collation, stable, case-order, or data-type attributes of an xsl:sort child of that xsl:for-each-group instruction.

ERR XTSE3230

It is a static error if the bind-grouping-key attribute is present on an xsl:for-each-group instruction unless either the group-by or group-adjacent attribute is present.

ERR XTSE3270

It is a static error if the set of variable names declared using the bind-group and bind-key attributes of an xsl:merge instruction and the bind-source attributes of its xsl:merge-source children contains any duplicates.

ERR XTSE3280

It is a static error if the select attribute of the xsl:map-entry element is present unless the element has has no children other than xsl:fallback elements.

ERR XTSE3340

It is a static error if an xsl:template declaration has the name xsl:initial-template and contains an xsl:param that specifies required="yes".

ERR XTSE3350

It is a static error for a package to contain two or more non-hidden accumulators with the same expanded QName and the same import precedence, unless there is another accumulator with the same expanded QName, and a higher import precedence.

ERR XTSE3360

It is a static error for a package to contain a non-hidden accumulator if either the pre-descent or post-descent functions have the same name as a non-hidden stylesheet function in the same package.

ERR XTSE3370

It is a static error if the the visibility attribute of a stylesheet parameter that specifies required="yes" and does not specify static="yes" is present with a value other than public, final, or abstract, or if an xsl:expose or xsl:accept declaration attempts to modify the visibility of such a component to a value other than public, final, or abstract.

ERR XTSE3430

It is a static error if the stylesheet contains a construct that is declared to be streamable but which is not guaranteed-streamable, unless the user has indicated that the processor is to handle this situation by processing the stylesheet without streaming or by making use of processor extensions to the streamability rules where available.

Type errors

ERR XTTE0505

It is a type error if the result of evaluating the sequence constructor cannot be converted to the required type.

ERR XTTE0510

It is a type error if an xsl:apply-templates instruction with no select attribute is evaluated when the context item is not a node.

ERR XTTE0570

It is a type error if the supplied value of a variable cannot be converted to the required type.

ERR XTTE0590

It is a type error if the conversion of the supplied value of a parameter to its required type fails.

ERR XTTE0600

If a default value is given explicitly, that is, if there is either a select attribute or a non-empty sequence constructor, then it is a type error if the default value cannot be converted to the required type, using the function conversion rules.

ERR XTTE0780

If the as attribute [of xsl:function ] is specified, then the result evaluated by the sequence constructor (see 5.8 Sequence Constructors) is converted to the required type, using the function conversion rules. It is a type error if this conversion fails.

ERR XTTE0790

If the value of a parameter to a stylesheet function cannot be converted to the required type, a type error is signaled.

ERR XTTE0950

It is a type error to use the xsl:copy or xsl:copy-of instruction to copy a node that has namespace-sensitive content if the copy-namespaces attribute has the value no and its explicit or implicit validation attribute has the value preserve. It is also a type error if either of these instructions (with validation="preserve") is used to copy an attribute having namespace-sensitive content, unless the parent element is also copied. A node has namespace-sensitive content if its typed value contains an item of type xs:QName or xs:NOTATION or a type derived therefrom. The reason this is an error is because the validity of the content depends on the namespace context being preserved.

ERR XTTE0990

It is a type error if the xsl:number instruction is evaluated, with no value or select attribute, when the context item is not a node.

ERR XTTE1000

It is a type error if the result of evaluating the select attribute of the xsl:number instruction is anything other than a single node.

ERR XTTE1020

If any sort key value, after atomization and any type conversion required by the data-type attribute, is a sequence containing more than one item, then the effect depends on whether the xsl:sort element is processed with XSLT 1.0 behavior. With XSLT 1.0 behavior, the effective sort key value is the first item in the sequence. In other cases, this is a type error.

ERR XTTE1100

It is a type error if the result of evaluating the group-adjacent expression is an empty sequence or a sequence containing more than one item, unless composite="yes" is specified.

ERR XTTE1510

If the validation attribute of an xsl:element, xsl:attribute, xsl:copy, xsl:copy-of, or xsl:result-document instruction, or the xsl:validation attribute of a literal result element, has the effective value strict, and schema validity assessment concludes that the validity of the element or attribute is invalid or unknown, a type error occurs. As with other type errors, the error may be signaled statically if it can be detected statically.

ERR XTTE1512

If the validation attribute of an xsl:element, xsl:attribute, xsl:copy, xsl:copy-of, or xsl:result-document instruction, or the xsl:validation attribute of a literal result element, has the effective value strict, and there is no matching top-level declaration in the schema, then a type error occurs. As with other type errors, the error may be signaled statically if it can be detected statically.

ERR XTTE1515

If the validation attribute of an xsl:element, xsl:attribute, xsl:copy, xsl:copy-of, or xsl:result-document instruction, or the xsl:validation attribute of a literal result element, has the effective value lax, and schema validity assessment concludes that the element or attribute is invalid, a type error occurs. As with other type errors, the error may be signaled statically if it can be detected statically.

ERR XTTE1535

It is a type error if the value of the type attribute of an xsl:copy or xsl:copy-of instruction refers to a complex type definition and one or more of the items being copied is an attribute node.

ERR XTTE1540

It is a type error if an [xsl:]type attribute is defined for a constructed element or attribute, and the outcome of schema validity assessment against that type is that the validity property of that element or attribute information item is other than valid.

ERR XTTE1545

A type error occurs if a type or validation attribute is defined (explicitly or implicitly) for an instruction that constructs a new attribute node, if the effect of this is to cause the attribute value to be validated against a type that is derived from, or constructed by list or union from, the primitive types xs:QName or xs:NOTATION.

ERR XTTE1550

A type error occurs [when a document node is validated] unless the children of the document node comprise exactly one element node, no text nodes, and zero or more comment and processing instruction nodes, in any order.

ERR XTTE1555

It is a type error if, when validating a document node, document-level constraints (such as ID/IDREF constraints) are not satisfied.

ERR XTTE2230

It is a type error if some item selected by a particular merge key in one input sequence is not comparable using the XPath le operator with some item selected by the corresponding sort key in another input sequence.

ERR XTTE3090

It is a type error if the xsl:context-item child of xsl:template specifies that a context item is required and none is supplied by the caller, that is, if the context item is absent at the point where xsl:call-template is evaluated.

ERR XTTE3100

It is a type error if an xsl:apply-templates instruction in a particular mode selects an element or attribute whose type is xs:untyped or xs:untypedAtomic when the typed attribute of that mode specifies the value yes, strict, or lax.

ERR XTTE3110

It is a type error if an xsl:apply-templates instruction in a particular mode selects an element or attribute whose type is anything other than xs:untyped or xs:untypedAtomic when the typed attribute of that mode specifies the value no.

ERR XTTE3170

It is a type error if the result of evaluating the namespace-context attribute of the xsl:evaluate instruction is anything other than a single node.

ERR XTTE3180

It is a type error if the result of evaluating the select expression [of the xsl:copy element] is a sequence of more than one item.

ERR XTTE3210

If the result of evaluating the context-item expression [of an xsl:evaluate instruction] is a sequence containing more than one item, then a type error is signaled.

ERR XTTE3300

It is a type error if the result of evaluating the xsl:on-empty attribute [on a literal result element] does not satisfy the required type element()?. That is, the expression must deliver either a single element node, or an empty sequence.

ERR XTTE3310

It is a type error if the result of evaluating the on-empty attribute [on the xsl:element instruction] does not satisfy the required type element()?. That is, the expression must deliver either a single element node, or an empty sequence.

ERR XTTE3320

It is a type error if the result of evaluating the on-empty attribute [on the xsl:attribute instruction] does not satisfy the required type attribute()?. That is, the expression must deliver either a single attribute node, or an empty sequence.

ERR XTTE3330

It is a type error if the result of evaluating the on-empty attribute [on the xsl:copy instruction] does not satisfy the required type node()?. That is, the expression must deliver either a single node, or an empty sequence.

ERR XTTE3375

A type error occurs if the result of evaluating the sequence constructor [within an xsl:map instruction] is not an instance of the required type map(*)*.

Dynamic errors

ERR XTDE0030

It is a dynamic error if the effective value of an attribute written using curly brackets, in a position where an attribute value template is permitted, is a value that is not one of the permitted values for that attribute. If the processor is able to detect the error statically (for example, when any XPath expressions within the curly brackets can be evaluated statically), then the processor may optionally signal this as a static error.

ERR XTDE0040

It is a dynamic error if the invocation of the stylesheet specifies a template name that does not match the expanded QName of a named template defined in the stylesheet, whose visibility is public or final.

ERR XTDE0041

It is a dynamic error if the invocation of the stylesheet specifies a function name and arity that does not match the expanded QName and arity of a named stylesheet function defined in the stylesheet, whose visibility is public or final.

ERR XTDE0044

It is a dynamic error if the invocation of the stylesheet specifies an initial mode and if no input sequence is supplied (either explicitly, or defaulted to the initial context item).

ERR XTDE0045

It is a dynamic error if the invocation of the stylesheet specifies an initial mode (other than the unnamed mode) that does not match either the expanded QName in the name attribute of an xsl:mode declaration, or the expanded QName in the mode attribute of any template defined in the stylesheet.

ERR XTDE0050

It is a dynamic error if a stylesheet declares a visible stylesheet parameter with required="yes" and no value for this parameter is supplied when the stylesheet is primed. A stylesheet parameter is visible if it is not masked by another global variable or parameter with the same name and higher import precedence. If the parameter is a static parameter then the value must be supplied prior to the static analysis phase.

ERR XTDE0060

It is a dynamic error if the initial template defines a template parameter that specifies required="yes".

ERR XTDE0160

It is a dynamic error if an element has an effective version of V (with V < 3.0) when the implementation does not support backwards compatible behavior for XSLT version V.

ERR XTDE0290

Where the result of evaluating an XPath expression (or an attribute value template) is required to be a lexical QName, or if it is permitted to be a lexical QName and the actual value takes the form of a lexical QName, then unless otherwise specified it is a dynamic error if the value has a prefix and the defining element has no namespace node whose name matches that prefix. This error may be signaled as a static error if the value of the expression can be determined statically.

ERR XTDE0410

It is a dynamic error if the result sequence used to construct the content of an element node contains a namespace node or attribute node that is preceded in the sequence by a node that is neither a namespace node nor an attribute node.

ERR XTDE0420

It is a dynamic error if the result sequence used to construct the content of a document node contains a namespace node or attribute node.

ERR XTDE0430

It is a dynamic error if the result sequence contains two or more namespace nodes having the same name but different string values (that is, namespace nodes that map the same prefix to different namespace URIs).

ERR XTDE0440

It is a dynamic error if the result sequence contains a namespace node with no name and the element node being constructed has a null namespace URI (that is, it is an error to define a default namespace when the element is in no namespace).

ERR XTDE0450

It is a dynamic error if the result sequence contains a function item.

ERR XTDE0540

It is a dynamic error if the conflict resolution algorithm for template rules leaves more than one matching template rule when the declaration of the relevant mode has an on-multiple-match attribute with the value fail.

ERR XTDE0555

It is a dynamic error if xsl:apply-templates, xsl:apply-imports or xsl:next-match is used to process a node using a mode whose declaration specifies on-no-match="fail" when there is no template rule in the stylesheet whose match pattern matches that node.

ERR XTDE0560

It is a dynamic error if xsl:apply-imports or xsl:next-match is evaluated when the current template rule is absent.

ERR XTDE0610

If an optional parameter has no select attribute and has an empty sequence constructor, and if there is an as attribute, then the default value of the parameter is an empty sequence. If the empty sequence is not a valid instance of the required type defined in the as attribute, then the parameter is treated as a required parameter, which means that it is a dynamic error if the caller supplies no value for the parameter.

ERR XTDE0640

In general, a circularity in a stylesheet is a dynamic error.

ERR XTDE0700

It is a dynamic error if a template that is invoked using xsl:apply-templates, xsl:apply-imports, or xsl:next-match declares a template parameter with required="yes" and no value for this parameter is supplied by the calling instruction. The same error is reported in the case of a tunnel parameter whether invoked using one of these three instructions or by xsl:call-template, as explained in 10.1.2 Tunnel Parameters.

ERR XTDE0820

It is a dynamic error if the effective value of the name attribute [of the xsl:element instruction] is not a lexical QName.

ERR XTDE0830

In the case of an xsl:element instruction with no namespace attribute, it is a dynamic error if the effective value of the name attribute is a lexical QName whose prefix is not declared in an in-scope namespace declaration for the xsl:element instruction.

ERR XTDE0835

It is a dynamic error if the effective value of the namespace attribute [of the xsl:element instruction] is not in the lexical space of the xs:anyURI datatype or if it is the string http://www.w3.org/2000/xmlns/.

ERR XTDE0850

It is a dynamic error if the effective value of the name attribute [of an xsl:attribute instruction] is not a lexical QName.

ERR XTDE0855

In the case of an xsl:attribute instruction with no namespace attribute, it is a dynamic error if the effective value of the name attribute is the string xmlns.

ERR XTDE0860

In the case of an xsl:attribute instruction with no namespace attribute, it is a dynamic error if the effective value of the name attribute is a lexical QName whose prefix is not declared in an in-scope namespace declaration for the xsl:attribute instruction.

ERR XTDE0865

It is a dynamic error if the effective value of the namespace attribute [of the xsl:attribute instruction] is not in the lexical space of the xs:anyURI datatype or if it is the string http://www.w3.org/2000/xmlns/.

ERR XTDE0890

It is a dynamic error if the effective value of the name attribute [of the xsl:processing-instruction instruction] is not both an NCNameNames and a PITargetXML.

ERR XTDE0905

It is a dynamic error if the string value of the new namespace node is not valid in the lexical space of the datatype xs:anyURI, or if it is the string http://www.w3.org/2000/xmlns/.

ERR XTDE0920

It is a dynamic error if the effective value of the name attribute [of the xsl:namespace instruction] is neither a zero-length string nor an NCNameNames, or if it is xmlns.

ERR XTDE0925

It is a dynamic error if the xsl:namespace instruction generates a namespace node whose name is xml and whose string value is not http://www.w3.org/XML/1998/namespace, or a namespace node whose string value is http://www.w3.org/XML/1998/namespace and whose name is not xml.

ERR XTDE0930

It is a dynamic error if evaluating the select attribute or the contained sequence constructor of an xsl:namespace instruction results in a zero-length string.

ERR XTDE0980

It is a dynamic error if any undiscarded item in the atomized sequence supplied as the value of the value attribute of xsl:number cannot be converted to an integer, or if the resulting integer is less than 0 (zero).

ERR XTDE1001

It is a dynamic error if the effective value of the start-at attribute of the xsl:number instruction is not in the lexical space of xs:integer. The error may be signaled statically if it can be detected statically.

ERR XTDE1030

It is a dynamic error if, for any sort key component, the set of sort key values evaluated for all the items in the initial sequence, after any type conversion requested, contains a pair of ordinary values for which the result of the XPath lt operator is an error.

ERR XTDE1035

It is a dynamic error if the collation attribute of xsl:sort (after resolving against the base URI) is not a URI that is recognized by the implementation as referring to a collation.

ERR XTDE1061

It is a dynamic error if the current-group function is used when the current group is absent , or when it is invoked in the course of evaluating a pattern. The error may be reported statically if it can be detected statically.

ERR XTDE1071

It is a dynamic error if the current-grouping-key function is used when the current grouping key is absent, or when it is invoked in the course of evaluating a pattern.. The error may be reported statically if it can be detected statically.

ERR XTDE1110

It is a dynamic error if the collation URI specified to xsl:for-each-group (after resolving against the base URI) is a collation that is not recognized by the implementation. (For notes, [see ERR XTDE1035].)

ERR XTDE1140

It is a dynamic error if the effective value of the regex attribute [of the xsl:analyze-string instruction] does not conform to the required syntax for regular expressions, as specified in [Functions and Operators]. If the regular expression is known statically (for example, if the attribute does not contain any expressions enclosed in curly brackets) then the processor may signal the error as a static error.

ERR XTDE1145

It is a dynamic error if the effective value of the flags attribute [of the xsl:analyze-string instruction] has a value other than the values defined in [Functions and Operators]. If the value of the attribute is known statically (for example, if the attribute does not contain any expressions enclosed in curly brackets) then the processor may signal the error as a static error.

ERR XTDE1160

When a URI reference [supplied to the document function] contains a fragment identifier, it is a dynamic error if the media type is not one that is recognized by the processor, or if the fragment identifier does not conform to the rules for fragment identifiers for that media type, or if the fragment identifier selects something other than a sequence of nodes (for example, if it selects a range of characters within a text node).

ERR XTDE1162

When a URI reference [supplied to the document function] is a relative reference, it is a dynamic error if no base URI is available to resolve the relative reference. This can arise for example when the URI is contained in a node that has no base URI (for example a parentless text node), or when the second argument to the function is a node that has no base URI, or when the base URI from the static context is undefined.

ERR XTDE1260

It is a dynamic error if the value [of the first argument to the key function] is not a valid QName, or if there is no namespace declaration in scope for the prefix of the QName, or if the name obtained by expanding the QName is not the same as the expanded name of any xsl:key declaration in the containing package. If the processor is able to detect the error statically (for example, when the argument is supplied as a string literal), then the processor may optionally signal this as a static error.

ERR XTDE1270

It is a dynamic error to call the key function with two arguments if there is no context node, or if the root of the tree containing the context node is not a document node; or to call the function with three arguments if the root of the tree containing the node supplied in the third argument is not a document node.

ERR XTDE1360

If the current function is evaluated within an expression that is evaluated when the context item is absent, a dynamic error occurs.

ERR XTDE1370

It is a dynamic error if the unparsed-entity-uri function is called when there is no context node, or when the root of the tree containing the context node is not a document node.

ERR XTDE1380

It is a dynamic error if the unparsed-entity-public-id function is called when there is no context node, or when the root of the tree containing the context node is not a document node.

ERR XTDE1390

It is a dynamic error if the value supplied as the $property-name argument [to the system-property function] is not a valid QName, or if there is no namespace declaration in scope for the prefix of the QName. If the processor is able to detect the error statically (for example, when the argument is supplied as a string literal), then the processor may optionally signal this as a static error.

ERR XTDE1400

It is a dynamic error if the argument [passed to the function-available function] does not evaluate to a string that is a valid EQName, or if the value is a lexical QName with a prefix for which no namespace declaration is present in the static context. If the processor is able to detect the error statically (for example, when the argument is supplied as a string literal), then the processor may optionally signal this as a static error.

ERR XTDE1420

It is a dynamic error if the arguments supplied to a call on an extension function do not satisfy the rules defined for that particular extension function, or if the extension function reports an error, or if the result of the extension function cannot be converted to an XPath value.

ERR XTDE1425

When the containing element is processed with XSLT 1.0 behavior, it is a dynamic error to evaluate an extension function call if no implementation of the extension function is available.

ERR XTDE1428

It is a dynamic error if the argument [passed to the type-available function] does not evaluate to a string that is a valid EQName, or if the value is a lexical QName with a prefix for which no namespace declaration is present in the static context. If the processor is able to detect the error statically (for example, when the argument is supplied as a string literal), then the processor may optionally signal this as a static error.

ERR XTDE1440

It is a dynamic error if the argument [passed to the element-available function] does not evaluate to a string that is a valid EQName, or if the value is a lexical QName with a prefix for which no namespace declaration is present in the static context. If the processor is able to detect the error statically (for example, when the argument is supplied as a string literal), then the processor may optionally signal this as a static error.

ERR XTDE1450

When a processor performs fallback for an extension instruction that is not recognized, if the instruction element has one or more xsl:fallback children, then the content of each of the xsl:fallback children must be evaluated; it is a dynamic error if it has no xsl:fallback children.

ERR XTDE1460

It is a dynamic error if the effective value of the format attribute [of an xsl:result-document element] is not a valid EQName, or if it does not match the expanded QName of an output definition in the stylesheet. If the processor is able to detect the error statically (for example, when the format attribute contains no curly brackets), then the processor may optionally signal this as a static error.

ERR XTDE1480

It is a dynamic error to evaluate the xsl:result-document instruction in temporary output state.

ERR XTDE1490

It is a dynamic error for a transformation to generate two or more final result trees with the same URI.

ERR XTDE1500

It is a dynamic error for a stylesheet to write to an external resource and read from the same resource during a single transformation, if the same absolute URI is used to access the resource in both cases.

ERR XTDE1665

A non-schema-aware processor must raise a dynamic error if the input to the processor includes a node with a type annotation other than xs:untyped or xs:untypedAtomic, or an atomic value of a type other than those which a basic XSLT processor supports.

ERR XTDE2210

It is a dynamic error if there are two xsl:merge-key elements that occupy corresponding positions among the xsl:merge-key children of two different xsl:merge-source elements and that have differing effective values for any of the attributes lang, order, collation, case-order, or data-type. Values are considered to differ if the attribute is present on one element and not on the other, or if it is present on both elements with effective values that are not equal to each other. In the case of the collation attribute, the values are compared as absolute URIs after resolving against the base URI.The error may be reported statically if it is detected statically.

ERR XTDE2220

It is a dynamic error if any input sequence to an xsl:merge instruction contains two items that are not correctly sorted according to the merge key values defined on the xsl:merge-key children of the corresponding xsl:merge-source element, when compared using the collation rules defined by the attributes of the corresponding xsl:merge-key children of the xsl:merge instruction, unless the attribute sort-before-merge is present with the value yes.

ERR XTDE3160

It is a dynamic error if the target expression [of an xsl:evaluate instruction] is not a valid XPath 3.0 expression (that is, if a static error occurs when analyzing the string according to the rules of the XPath 3.0 specification).

ERR XTDE3175

It is a dynamic error if an xsl:evaluate instruction is evaluated when use of xsl:evaluate has been statically or dynamically disabled.

ERR XTDE3240

It is a dynamic error if the value of $input does not conform to the JSON grammar, as selected using the explicit or implicit spec option.

ERR XTDE3245

It is a dynamic error if the value of the validate option is true and the processor is not schema-aware.

ERR XTDE3250

It is a dynamic error if the value of $input contains an escaped representation of a character (or codepoint) that is not a valid character in the version of XML supported by the implementation, unless the unescape option is set to false.

ERR XTDE3260

It is a dynamic error if the value of $options includes an entry whose key is "spec" and whose value is not a single xs:string, or an entry whose key is "validate" or "unescape" and whose value is not a single xs:boolean.

ERR XTDE3340

It is a dynamic error if the value [of the first argument to the accumulator-before or accumulator-after function] is not a valid EQName, or if there is no namespace declaration in scope for the prefix of the QName, or if the name obtained by expanding the QName is not the same as the expanded name of any xsl:accumulator declaration visible in the package in which the function call appears. If the processor is able to detect the error statically (for example, when the argument is supplied as a string literal), then the processor may optionally signal this as a static error.

ERR XTDE3350

It is a dynamic error to call the accumulator-before or accumulator-after function when there is no context item.

ERR XTTE3360

It is a type error to call the accumulator-before or accumulator-after function when the context item is not a node, or when it is an attribute or namespace node.

ERR XTDE3365

A dynamic error occurs if the set of keys in the maps resulting from evaluating the sequence constructor [within an xsl:map instruction] contains duplicates.

ERR XTDE3370

It is a dynamic error if the accumulator-before or accumulator-after function is called and (a) the accumulator has the property streamable="no", and (b) the context item is a node in a streamed document.

ERR XTDE3380

If the accumulator is declared with the attribute streamable="yes" then it is a dynamic error if the accumulator-before or accumulator-after function is called unless the evaluation is performed in the course of the evaluation of either (a) the sequence constructor contained in a template rule invoked in a mode declared with streamable="yes", or (b) the sequence constructor contained in an xsl:stream instruction, or both. Call the nearest such construct in the chain of causation the controlling sequence constructor.

ERR XTDE3390

If the accumulator is declared with the attribute streamable="yes" then it is a dynamic error if the accumulator-before or accumulator-after function is called unless the context item at the point of evaluating this function is the same node as the context item for the evaluation of the controlling sequence constructor.

ERR XTDE3400

It is a dynamic error if the accumulator-before or accumulator-after function for an accumulator A is evaluated in the course of evaluating the new-value expression of any accumulator rule for the same accumulator A.

ERR XTDE3410

If the accumulator is declared with the attribute streamable="yes" then it is a dynamic error if the accumulator-before function is called unless the evaluation is performed in the course of the evaluation of a pre-descent instruction within the controlling sequence constructor.

ERR XTDE3420

If the accumulator is declared with the attribute streamable="yes" then it is a dynamic error if the accumulator-after function is called unless the evaluation is performed in the course of the evaluation of a post-descent instruction within the controlling sequence constructor.

ERR XTMM9000

When a transformation is terminated by use of xsl:message terminate="yes", the effect is the same as when a dynamic error occurs during the transformation. The default error code is XTMM9000; this may be overridden using the error-code attribute of the xsl:message instruction.

ERR XTMM9001

When a transformation is terminated by use of xsl:assert, the effect is the same as when a dynamic error occurs during the transformation. The default error code is XTMM9001; this may be overridden using the error-code attribute of the xsl:assert instruction.

F Checklist of Implementation-Defined Features (Non-Normative)

This appendix provides a summary of XSLT language features whose effect is explicitly implementation-defined. The conformance rules (see 26 Conformance) require vendors to provide documentation that explains how these choices have been exercised.

  1. The way in which a base output URI is established is implementation-defined (See 2.3.2 Priming a Stylesheet)

  2. The way in which an XSLT processor is invoked, and the way in which values are supplied for the source document, starting node, stylesheet parameters, and base output URI, are implementation-defined. (See 2.3.2 Priming a Stylesheet)

  3. The mechanisms for creating new extension instructions and extension functions are implementation-defined. (See 2.8 Extensibility)

  4. It is implementation-defined whether type errors are signaled statically. (See 2.11 Error Handling)

  5. Mechanisms to locate the source or executable code of a package are implementation-defined. (See 3.6.1 Dependencies between Packages)

  6. The set of namespaces that are specially recognized by the implementation (for example, for user-defined data elements, and extension attributes) is implementation-defined. (See 3.8.3 User-defined Data Elements)

  7. The effect of user-defined data elements whose name is in a namespace recognized by the implementation is implementation-defined. (See 3.8.3 User-defined Data Elements)

  8. If the effective version of any element in the stylesheet is not 1.0 or 2.0 but is less than 3.0, the recommended action is to report a static error; however, processors may recognize such values and process the element in an implementation-defined way. (See 3.10 Backwards Compatible Processing)

  9. It is implementation-defined whether an XSLT 3.0 processor supports backwards compatible behavior for any XSLT version earlier than XSLT 3.0. (See 3.10 Backwards Compatible Processing)

  10. It is implementation-defined what forms of URI reference are acceptable in the href attribute of the xsl:include and xsl:import elements, for example, the URI schemes that may be used, the forms of fragment identifier that may be used, and the media types that are supported. (See 3.12.1 Locating Stylesheet Modules)

  11. An implementation may define mechanisms, above and beyond xsl:import-schema that allow schema components such as type definitions to be made available within a stylesheet. (See 3.15 Built-in Types)

  12. It is implementation-defined which versions of XML and XML Namespaces (1.0 and/or 1.1) are supported. (See 4.1 XML Versions)

  13. Limits on the value space of primitive datatypes, where not fixed by [XML Schema Part 2], are implementation-defined. (See 4.7 Limits)

  14. The set of statically known documentsXP30 is implementation-defined. (See 5.4.1 Initializing the Static Context)

  15. The set of statically known collectionsXP30 is implementation-defined. (See 5.4.1 Initializing the Static Context)

  16. The statically known default collection typeXP30 is implementation-defined. (See 5.4.1 Initializing the Static Context)

  17. Implementations may provide user options that relax the requirement for the docFO30 and collectionFO30 functions (and therefore, by implication, the document function) to return stable results. The manner in which such user options are provided, if at all, is implementation-defined. (See 5.4.3 Initializing the Dynamic Context)

  18. The implicit timezone for a transformation is implementation-defined. (See 5.4.3.2 Other Components of the XPath Dynamic Context)

  19. The default collectionXP30 is implementation-defined. (See 5.4.3.2 Other Components of the XPath Dynamic Context)

  20. The availability of dynamic context information within extension functions is implementation-defined. (See 5.4.4 Additional Dynamic Context Components used by XSLT)

  21. The default values for the warning-on-no-match and warning-on-multiple-match attributes of xsl:mode are implementation-defined. (See 6.6.1 Declaring Modes)

  22. The form of any warnings output when there is no matching template rule or when there are multiple matching template rules is implementation-defined. (See 6.6.1 Declaring Modes)

  23. The mechanism by which the caller supplies a value for a stylesheet parameter is implementation-defined. (See 9.5 Global Variables and Parameters)

  24. The set of extension functions available in the static context for the target expression of xsl:evaluate is implementation-defined. (See 10.4.1 Static context for the target expression)

  25. If an xml:id attribute that has not been subjected to attribute value normalization is copied from a source tree to a result tree, it is implementation-defined whether attribute value normalization will be applied during the copy process. (See 11.9.1 Shallow Copy)

  26. The numbering sequences supported by the xsl:number instructions, beyond those defined in this specification, are implementation-defined. (See 12.3 Number to String Conversion Attributes)

  27. There may be implementation-defined upper bounds on the numbers that can be formatted by xsl:number using any particular numbering sequence. (See 12.3 Number to String Conversion Attributes)

  28. The set of languages for which numbering is supported by xsl:number, and the method of choosing a default language, are implementation-defined. (See 12.3 Number to String Conversion Attributes)

  29. With xsl:number, it is implementation-defined what combinations of values of the format token, the language, and the ordinal attribute are supported. (See 12.3 Number to String Conversion Attributes)

  30. If the data-type attribute of the xsl:sort element has a value other than text or number, the effect is implementation-defined. (See 13.1.2 Comparing Sort Key Values)

  31. The facilities for defining collations and allocating URIs to identify them are implementation-defined. (See 13.1.3 Sorting Using Collations)

  32. The algorithm used by xsl:sort to locate a collation, given the values of the lang and case-order attributes, is implementation-defined. (See 13.1.3 Sorting Using Collations)

  33. The set of media types recognized by the processor, for the purpose of interpreting fragment identifiers in URI references passed to the document function, is implementation-defined. (See 20.1 fn:document)

  34. The values returned by the system-property function, and the names of the additional properties that are recognized, are implementation-defined. (See 20.3.4 fn:system-property)

  35. The destination and formatting of messages written using the xsl:message instruction are implementation-defined. (See 22.1 Messages)

  36. The detail of any external mechanism allowing a processor to disable checking of assertions is implementation-defined. (See 22.2 Assertions)

  37. This specification does not define any mechanism for creating or binding implementations of extension instructions or extension functions, and it is not required that implementations support any such mechanism. Such mechanisms, if they exist, are implementation-defined. (See 23 Extensibility and Fallback)

  38. The effect of an extension function returning a string containing characters that are not permitted in XML is implementation-defined. (See 23.1.2 Calling Extension Functions)

  39. The way in which external objects are represented in the type system is implementation-defined. (See 23.1.3 External Objects)

  40. The way in which a final result tree is delivered to an application is implementation-defined. (See 24 Final Result Trees)

  41. There may be implementation-defined restrictions on the form of absolute URI that may be used in the href attribute of the xsl:result-document instruction. (See 24.1 Creating Final Result Trees)

  42. Implementations may provide additional mechanisms allowing users to define the way in which final result trees are processed. (See 24.1 Creating Final Result Trees)

  43. If serialization is supported, then the location to which a final result tree is serialized is implementation-defined, subject to the constraint that relative URI references used to reference one tree from another remain valid. (See 25 Serialization)

  44. The default value of the encoding attribute of the xsl:output element is implementation-defined. (See 25 Serialization)

  45. It is implementation-defined which versions of XML, HTML, and XHTML are supported in the version attribute of the xsl:output declaration. (See 25 Serialization)

  46. The default value of the byte-order-mark serialization parameter is implementation-defined in the case of UTF-8 encoding. (See 25 Serialization)

  47. It is implementation-defined whether, and under what circumstances, disabling output escaping is supported. (See 25.2 Disabling Output Escaping)

G List of XSLT-defined functions (Non-Normative)

This appendix acts as an index of functions defined in this specification, to augment the set of functions defined in [Functions and Operators].

accumulator-after
See 18.2.5 fn:accumulator-after
accumulator-before
See 18.2.4 fn:accumulator-before
collation-key
See 21.1.2.8 fn:collation-key
copy-of
See 18.3 fn:copy-of
current
See 20.3.1 fn:current
current-group
See 14.2.1 fn:current-group
current-grouping-key
See 14.2.2 fn:current-grouping-key
deep-equal
See 21.1.2.10 fn:deep-equal
document
See 20.1 fn:document
element-available
See 23.2.2 fn:element-available
function-available
See 23.1.1 fn:function-available
json-to-xml
See 21.2.2 fn:json-to-xml
key
See 20.2.2 fn:key
map:contains
See 21.1.2.3 map:contains
map:entry
See 21.1.2.5 map:entry
map:for-each-entry
See 21.1.2.7 map:for-each-entry
map:get
See 21.1.2.4 map:get
map:keys
See 21.1.2.2 map:keys
map:new
See 21.1.2.1 map:new
map:remove
See 21.1.2.6 map:remove
regex-group
See 17.2 fn:regex-group
snapshot
See 18.4 fn:snapshot
system-property
See 20.3.4 fn:system-property
type-available
See 23.1.4 fn:type-available
unparsed-entity-public-id
See 20.3.3 fn:unparsed-entity-public-id
unparsed-entity-uri
See 20.3.2 fn:unparsed-entity-uri

H Schema for XSLT Stylesheets (Non-Normative)

The following XSD 1.1 schema describes the structure of an XSLT stylesheet module. It does not define all the constraints that apply to a stylesheet (for example, it does not attempt to define a datatype that precisely represents attributes containing XPath expressions). However, every valid stylesheet module conforms to this schema, unless it contains elements that invoke forwards compatible behavior.

A copy of this schema is available at http://www.w3.org/2012/07/schema-for-xslt30.xsd

Note:

The schema as written uses a lax wildcard to permit literal result elements to appear in a sequence constructor. This assumes that the schema used for validation will not contain any global element declaration that matches the element name of a literal result element. The content model for an element such as invoice appearing within a stylesheet is not the same as the content model for the same element appearing within a source document (it is likely to contain XSLT instructions rather than other elements from the target vocabulary): therefore, including such declarations in the schema used for validating a stylesheet is inappropriate.

The reason that lax validation rather than skip validation is used is so that XSLT instructions appearing as children of the literal result element will themselves be validated, using the appropriate global element declaration.

Note:

The schema uses XSD 1.1 assertions to represent some of the non-grammatical constraints appearing in the specification, for example the rule that some elements can have either a select attribute or a contained sequence constructor, but not both. At this stage, no attempt has been made to represent every such constraint, even where it is not difficult to express the rule. There will always be some constraints that cannot be expressed at all, for example those that require access to multiple stylesheet modules, those that require access to the in-scope schema components, and those that involve parsing a non-regular grammar, such as the grammar for patterns.

Apart from assertions, the only other significant use of XSD 1.1 features is that the elements xsl:param and xsl:variable are in two substitution groups: one containing all instructions, and one containing all declarations. If the schema needs to be converted to an XSD 1.0 schema, removing all assertions is straightforward; the other change needed is to remove xsl:param and xsl:variable from the substitution group for declarations, and instead permit them explicitly as children of xsl:transform.

<?xml version="1.0" encoding="UTF-8"?>
<!--* <!DOCTYPE xs:schema PUBLIC "-//W3C//DTD XMLSCHEMA 200105//EN"
       "http://www.w3.org/2001/XMLSchema.dtd" [
<!ENTITY % schemaAttrs "
  xmlns:xs   CDATA #IMPLIED
  xmlns:xsl  CDATA #IMPLIED
  xmlns:xsd  CDATA #IMPLIED"
>
<!ENTITY % p "xs:">
<!ENTITY % s ":xs">
]> *-->

<?xml-stylesheet href="http://www.w3.org/2008/09/xsd.xsl" type="text/xsl"?> 
<!--* <?xml-stylesheet href="http://www.w3.org/2008/09/xsd.xsl" type="application/xslt+xml"?>  *-->
<!--* <?xml-stylesheet href="../../../www.w3.org/2008/09/xsd.xsl" type="application/xslt+xml"?> *-->

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  targetNamespace="http://www.w3.org/1999/XSL/Transform" elementFormDefault="qualified">

  <!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
  <xs:annotation>
    <xs:documentation>
      <p>This is an XSD 1.1 schema for XSLT 3.0 stylesheets.
      It defines all the elements that appear in the XSLT namespace; it also provides hooks that
      allow the inclusion of user-defined literal result elements, extension instructions, and
      top-level data elements.</p>
      
      <p>This schema is available for use under the conditions of the W3C
      Software License published at http://www.w3.org/Consortium/Legal/copyright-software-19980720</p>
      
      <p>The schema is organized as follows:</p>
      <ul>
         <li>PART A: definitions of complex types and model groups used
         as the basis for element definitions</li>
         <li>PART B: definitions of individual XSLT elements</li> 
         <li>PART C: definitions for literal result elements</li> 
         <li>PART D: definitions of simple types used in attribute definitions</li>
      </ul>
      
      <p>The schema has a number of limitations:</p>
      <ul>
        <li>The XSLT specification allows additional elements and attributes to be present
        where forwards compatibility is invoked. This schema does not.</li>
        <li>The XSLT specification allows arbitrary content in a part of the stylesheet
        that is excluded by virtue of a use-when attribute. This schema does not.</li>
        <li>The handling of literal result elements in this schema is imperfect; although
        various options are allowed, none matches the specification exactly. For example,
        the content of a literal result element uses lax validation, which permits child
        elements in the XSLT namespace that have no declaration in this schema.</li>
        <li>The schema makes no attempt to check XPath expressions for syntactic or
        semantic correctness, nor to check that component references are resolved (for example
        that a template named in xsl:call-template has a declaration). Doing this in general
        requires cross-document validation, which is beyond the scope of XSD.</li>
        <li>The schema imports the schema for XSD 1.0 schema documents. In stylesheets that contain
        an inline XSD 1.1 schema, this import should be replaced with one for the schema for XSD 1.1
        schema documents.</li>
       </ul>
    </xs:documentation>
  </xs:annotation>
  <!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

  <!--
The declaration of xml:space and xml:lang may need to be commented out because
of problems processing the schema using various tools
-->

  <xs:import namespace="http://www.w3.org/XML/1998/namespace"/>
  <!--schemaLocation="http://www.w3.org/2001/xml.xsd"-->

  <!-- 
    An XSLT stylesheet may contain an in-line schema within an xsl:import-schema element,
    so the Schema for schemas needs to be imported
-->

  <xs:import namespace="http://www.w3.org/2001/XMLSchema"
    schemaLocation="http://www.w3.org/2001/XMLSchema.xsd"/>

  <!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
  <xs:annotation>
    <xs:documentation> PART A: definitions of complex types and model groups used as the basis for
      element definitions </xs:documentation>
  </xs:annotation>
  <!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

  <xs:complexType name="generic-element-type" mixed="true">
    <xs:annotation>
        <xs:documentation>
            <p>This complex type provides a generic supertype for all XSLT elements; it contains the
                definitions of the standard attributes that may appear on any element.</p>    
        </xs:documentation>
    </xs:annotation>
    <xs:attribute name="default-collation" type="xsl:uri-list"/>
    <xs:attribute name="default-mode" type="xsl:default-mode-type"/>
    <xs:attribute name="default-validation" type="xsl:validation-strip-or-preserve"
      default="strip"/>
    <xs:attribute name="exclude-result-prefixes" type="xsl:prefix-list-or-all"/>
    <xs:attribute name="expand-text" type="xsl:yes-or-no"/>
    <xs:attribute name="extension-element-prefixes" type="xsl:prefix-list"/>
    <xs:attribute name="use-when" type="xsl:expression"/>
    <xs:attribute name="xpath-default-namespace" type="xs:anyURI"/>
    <xs:anyAttribute namespace="##other" processContents="lax"/>
  </xs:complexType>

  <xs:complexType name="versioned-element-type" mixed="true">
    <xs:annotation>
        <xs:documentation>
            <p>This complex type provides a generic supertype for all XSLT elements with
                the exception of <code>xsl:output</code>; it contains the
                definitions of the <code>version</code> attribute that may appear on any element.
                </p>
             <p>The <code>xsl:output</code> does not use this definition because, although it
             has a <code>version</code> attribute, the syntax and semantics of this attribute are
             unrelated to the standard <code>version</code> attribute allowed on other elements.</p>    
        </xs:documentation>
    </xs:annotation>
    <xs:complexContent>
      <xs:extension base="xsl:generic-element-type">
        <xs:attribute name="version" type="xs:decimal" use="optional"/>
      </xs:extension>
    </xs:complexContent>
  </xs:complexType>

  <xs:complexType name="element-only-versioned-element-type" mixed="false">
    <xs:complexContent>
      <xs:restriction base="xsl:versioned-element-type">
        <xs:anyAttribute namespace="##other" processContents="lax"/>
      </xs:restriction>
    </xs:complexContent>
  </xs:complexType>

  <xs:complexType name="sequence-constructor">
    <xs:annotation>
        <xs:documentation>
            <p>This complex type provides a generic supertype for all XSLT elements that
                allow a sequence constructor as their content.
                </p>
        </xs:documentation>
    </xs:annotation>
    <xs:complexContent mixed="true">
      <xs:extension base="xsl:versioned-element-type">
        <xs:group ref="xsl:sequence-constructor-group" minOccurs="0" maxOccurs="unbounded"/>
      </xs:extension>
    </xs:complexContent>
  </xs:complexType>
  
  <xs:complexType name="sequence-constructor-and-select">
    <xs:annotation>
      <xs:documentation>
        <p>This complex type allows a sequence constructor and a select attribute.</p>
      </xs:documentation>
    </xs:annotation>
    <xs:complexContent mixed="true">
      <xs:extension base="xsl:sequence-constructor">
        <xs:attribute name="select" type="xsl:expression"/>
      </xs:extension>
    </xs:complexContent>
  </xs:complexType>
  
  <xs:complexType name="sequence-constructor-or-select">
    <xs:annotation>
      <xs:documentation>
        <p>This complex type allows a sequence constructor or a select attribute, but not both.</p>
      </xs:documentation>
    </xs:annotation>
    <xs:complexContent mixed="true">
      <xs:restriction base="xsl:sequence-constructor-and-select">
        <xs:group ref="xsl:sequence-constructor-group" minOccurs="0" maxOccurs="unbounded"/>
        <xs:anyAttribute namespace="##other" processContents="lax"/>
        <xs:assert test="not(exists(@select) and (exists(* except xsl:fallback) or exists(text()[normalize-space()])))"/>
      </xs:restriction>
    </xs:complexContent>
  </xs:complexType>

  <xs:group name="sequence-constructor-group">
    <xs:annotation>
        <xs:documentation>
            <p>This complex type provides a generic supertype for all XSLT elements that
                allow a sequence constructor as their content.
                </p>
        </xs:documentation>
    </xs:annotation>
    <xs:choice>
      <xs:element ref="xsl:instruction"/>
      <xs:group ref="xsl:result-elements"/>
    </xs:choice>
  </xs:group>

  <xs:element name="declaration" type="xsl:generic-element-type" abstract="true"/>

  <xs:element name="instruction" type="xsl:versioned-element-type" abstract="true"/>

  <!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
  <xs:annotation>
    <xs:documentation> 
      PART B: definitions of individual XSLT elements 
      Elements are listed in alphabetical order. 
    </xs:documentation>
  </xs:annotation>
  <!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
  
  <xs:element name="accept">
    <xs:annotation>
        <xs:documentation>
            <p>This element appears as a child of <code>xsl:use-package</code> and defines 
            any variations that the containing package wishes to make to the visibility of
            components made available from a library package. For example, it may indicate that
            some of the public components in the library package are not to be made available
            to the containing package.</p>
        </xs:documentation>
    </xs:annotation>
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:attribute name="component" type="xsl:component-kind-type" use="required"/>
          <xs:attribute name="names" type="xsl:EQNames" use="required"/>
          <xs:attribute name="visibility" type="xsl:visibility-type" use="required"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>
  
  <xs:element name="accumulator" substitutionGroup="xsl:declaration">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:sequence>
            <xs:element ref="xsl:accumulator-rule" minOccurs="1"  maxOccurs="unbounded"/>
          </xs:sequence>
          <xs:attribute name="name" type="xsl:EQName" />
          <xs:attribute name="post-descent" type="xsl:EQName" />
          <xs:attribute name="initial-value" type="xsl:expression"/>
          <xs:attribute name="as" type="xsl:sequence-type"/>
          <xs:attribute name="visibility" type="xsl:visibility-type"/>
          <xs:attribute name="streamable" type="xsl:yes-or-no"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="accumulator-rule">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:sequence/>
          <xs:attribute name="match" type="xsl:pattern" use="required"/>
          <xs:attribute name="phase">
            <xs:simpleType>
              <xs:restriction base="xs:token">
                <xs:enumeration value="start"/>
                <xs:enumeration value="end"/>
              </xs:restriction>           
            </xs:simpleType>
          </xs:attribute>
          <xs:attribute name="new-value" type="xsl:expression" use="required"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="analyze-string" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:sequence>
            <xs:element ref="xsl:matching-substring" minOccurs="0"/>
            <xs:element ref="xsl:non-matching-substring" minOccurs="0"/>
            <xs:element ref="xsl:fallback" minOccurs="0" maxOccurs="unbounded"/>
          </xs:sequence>
          <xs:attribute name="select" type="xsl:expression" use="required"/>
          <xs:attribute name="regex" type="xsl:avt" use="required"/>
          <xs:attribute name="flags" type="xsl:avt" default=""/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="apply-imports" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:sequence>
            <xs:element ref="xsl:with-param" minOccurs="0" maxOccurs="unbounded"/>
          </xs:sequence>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="apply-templates" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:choice minOccurs="0" maxOccurs="unbounded">
            <xs:element ref="xsl:sort"/>
            <xs:element ref="xsl:with-param"/>
          </xs:choice>
          <xs:attribute name="select" type="xsl:expression" default="child::node()"/>
          <xs:attribute name="mode" type="xsl:mode"/>
          <xs:assert test="every $e in subsequence(xsl:sort, 2) satisfies empty($e/@stable)">
            <xs:annotation>
              <xs:documentation>
                <p>It is a static error if an xsl:sort element other than the first in a 
                  sequence of sibling xsl:sort elements has a stable attribute.
                </p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>
  
  <xs:element name="assert" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:sequence-constructor">
          <xs:attribute name="test" type="xsl:expression" use="required"/>
          <xs:attribute name="select" type="xsl:expression"/>
          <xs:attribute name="error-code" type="xsl:avt"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="attribute" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:sequence-constructor-or-select">
          <xs:attribute name="name" type="xsl:avt" use="required"/>
          <xs:attribute name="namespace" type="xsl:avt"/>
          <xs:attribute name="separator" type="xsl:avt"/>
          <xs:attribute name="type" type="xsl:EQName"/>
          <xs:attribute name="validation" type="xsl:validation-type"/>
          <xs:attribute name="on-empty" type="xsl:expression"/>
          <xs:assert test="not(exists(@type) and exists(@validation))">
            <xs:annotation>
              <xs:documentation>
                <p>The <code>type</code> and <code>validation</code> attributes are mutually exclusive
                (if one is present, the other must be absent).</p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="attribute-set" substitutionGroup="xsl:declaration">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:sequence minOccurs="0" maxOccurs="unbounded">
            <xs:element ref="xsl:attribute"/>
          </xs:sequence>
          <xs:attribute name="name" type="xsl:EQName" use="required"/>
          <xs:attribute name="streamable" type="xsl:yes-or-no"/>
          <xs:attribute name="use-attribute-sets" type="xsl:EQNames" default=""/>
          <xs:attribute name="visibility" type="xsl:visibility-type"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="break" substitutionGroup="xsl:instruction" type="xsl:sequence-constructor-or-select"/>

  <xs:element name="call-template" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:sequence>
            <xs:element ref="xsl:with-param" minOccurs="0" maxOccurs="unbounded"/>
          </xs:sequence>
          <xs:attribute name="name" type="xsl:EQName" use="required"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="catch">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:sequence-constructor-or-select">
          <xs:attribute name="errors" type="xs:token" use="optional"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="character-map" substitutionGroup="xsl:declaration">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:sequence>
            <xs:element ref="xsl:output-character" minOccurs="0" maxOccurs="unbounded"/>
          </xs:sequence>
          <xs:attribute name="name" type="xsl:EQName" use="required"/>
          <xs:attribute name="use-character-maps" type="xsl:EQNames" default=""/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="choose" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:sequence>
            <xs:element ref="xsl:when" maxOccurs="unbounded"/>
            <xs:element ref="xsl:otherwise" minOccurs="0"/>
          </xs:sequence>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="comment" substitutionGroup="xsl:instruction" type="xsl:sequence-constructor-or-select"/>

  <xs:element name="context-item">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:attribute name="as" type="xsl:item-type"/>
          <xs:attribute name="use">
            <xs:simpleType>
              <xs:restriction base="xs:token">
                <xs:enumeration value="required"/>
                <xs:enumeration value="optional"/>
                <xs:enumeration value="prohibited"/>
              </xs:restriction>
            </xs:simpleType>
          </xs:attribute>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="copy" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:sequence-constructor">
          <xs:attribute name="select" type="xsl:expression"/>
          <xs:attribute name="copy-namespaces" type="xsl:yes-or-no" default="yes"/>
          <xs:attribute name="inherit-namespaces" type="xsl:yes-or-no" default="yes"/>
          <xs:attribute name="use-attribute-sets" type="xsl:EQNames" default=""/>
          <xs:attribute name="type" type="xsl:EQName"/>
          <xs:attribute name="validation" type="xsl:validation-type"/>
          <xs:attribute name="on-empty" type="xsl:expression"/>
          <xs:assert test="not(exists(@type) and exists(@validation))">
            <xs:annotation>
              <xs:documentation>
                <p>The <code>type</code> and <code>validation</code> attributes are mutually exclusive
                  (if one is present, the other must be absent).</p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="copy-of" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:versioned-element-type">
          <xs:attribute name="select" type="xsl:expression" use="required"/>
          <xs:attribute name="copy-namespaces" type="xsl:yes-or-no" default="yes"/>
          <xs:attribute name="type" type="xsl:EQName"/>
          <xs:attribute name="validation" type="xsl:validation-type"/>
          <xs:assert test="not(exists(@type) and exists(@validation))">
            <xs:annotation>
              <xs:documentation>
                <p>The <code>type</code> and <code>validation</code> attributes are mutually exclusive
                  (if one is present, the other must be absent).</p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="document" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:sequence-constructor">
          <xs:attribute name="type" type="xsl:EQName"/>
          <xs:attribute name="validation" type="xsl:validation-type"/>
          <xs:assert test="not(exists(@type) and exists(@validation))">
            <xs:annotation>
              <xs:documentation>
                <p>The <code>type</code> and <code>validation</code> attributes are mutually exclusive
                  (if one is present, the other must be absent).</p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="decimal-format" substitutionGroup="xsl:declaration">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:attribute name="name" type="xsl:EQName"/>
          <xs:attribute name="decimal-separator" type="xsl:char" default="."/>
          <xs:attribute name="grouping-separator" type="xsl:char" default=","/>
          <xs:attribute name="infinity" type="xs:string" default="Infinity"/>
          <xs:attribute name="minus-sign" type="xsl:char" default="-"/>
          <xs:attribute name="NaN" type="xs:string" default="NaN"/>
          <xs:attribute name="percent" type="xsl:char" default="%"/>
          <xs:attribute name="per-mille" type="xsl:char" default="~"/>
          <xs:attribute name="zero-digit" type="xsl:zero-digit" default="0"/>
          <xs:attribute name="digit" type="xsl:char" default="#"/>
          <xs:attribute name="pattern-separator" type="xsl:char" default=";"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="element" substitutionGroup="xsl:instruction">
    <xs:complexType mixed="true">
      <xs:complexContent>
        <xs:extension base="xsl:sequence-constructor">
          <xs:attribute name="name" type="xsl:avt" use="required"/>
          <xs:attribute name="namespace" type="xsl:avt"/>
          <xs:attribute name="inherit-namespaces" type="xsl:yes-or-no" default="yes"/>
          <xs:attribute name="use-attribute-sets" type="xsl:EQNames" default=""/>
          <xs:attribute name="type" type="xsl:EQName"/>
          <xs:attribute name="validation" type="xsl:validation-type"/>
          <xs:attribute name="on-empty" type="xsl:expression"/>
          <xs:assert test="not(exists(@type) and exists(@validation))">
            <xs:annotation>
              <xs:documentation>
                <p>The <code>type</code> and <code>validation</code> attributes are mutually exclusive
                  (if one is present, the other must be absent).</p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="evaluate" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:choice minOccurs="0" maxOccurs="unbounded">
            <xs:element ref="xsl:with-param"/>
            <xs:element ref="xsl:fallback"/>
          </xs:choice>
          <xs:attribute name="xpath" type="xsl:expression" use="required"/>
          <xs:attribute name="as" type="xsl:sequence-type"/>
          <xs:attribute name="base-uri" type="xsl:avt"/>
          <xs:attribute name="context-item" type="xsl:expression"/>
          <xs:attribute name="namespace-context" type="xsl:expression"/>
          <xs:attribute name="schema-aware" type="xsl:avt"/>
          <xs:attribute name="with-params" type="xsl:expression"/>         
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>
  
  <xs:element name="expose">
    <xs:annotation>
        <xs:documentation>
            <p>This element appears as a child of <code>xsl:use-package</code> and defines 
            the visibility of components that are made available (or not) by this package
            to other using packages.</p>
        </xs:documentation>
    </xs:annotation>
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:attribute name="component" type="xsl:component-kind-type"/>
          <xs:attribute name="names" type="xsl:EQNames"/>
          <xs:attribute name="visibility" type="xsl:visibility-not-hidden-type"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="fallback" substitutionGroup="xsl:instruction" type="xsl:sequence-constructor"/>

  <xs:element name="for-each" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:versioned-element-type">
          <xs:sequence>
            <xs:element ref="xsl:sort" minOccurs="0" maxOccurs="unbounded"/>
            <xs:group ref="xsl:sequence-constructor-group" minOccurs="0" maxOccurs="unbounded"/>
          </xs:sequence>
          <xs:attribute name="select" type="xsl:expression" use="required"/>
          <xs:assert test="every $e in subsequence(xsl:sort, 2) satisfies empty($e/@stable)">
            <xs:annotation>
              <xs:documentation>
                <p>It is a static error if an xsl:sort element other than the first in a 
                  sequence of sibling xsl:sort elements has a stable attribute.
                </p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="for-each-group" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:versioned-element-type">
          <xs:sequence>
            <xs:element ref="xsl:sort" minOccurs="0" maxOccurs="unbounded"/>
            <xs:group ref="xsl:sequence-constructor-group" minOccurs="0" maxOccurs="unbounded"/>
          </xs:sequence>
          <xs:attribute name="select" type="xsl:expression" use="required"/>
          <xs:attribute name="group-by" type="xsl:expression"/>
          <xs:attribute name="group-adjacent" type="xsl:expression"/>
          <xs:attribute name="group-starting-with" type="xsl:pattern"/>
          <xs:attribute name="group-ending-with" type="xsl:pattern"/>
          <xs:attribute name="bind-group" type="xsl:EQName"/>
          <xs:attribute name="bind-grouping-key" type="xsl:EQName"/>
          <xs:attribute name="composite" type="xsl:yes-or-no"/>
          <xs:attribute name="collation" type="xsl:avt"/>
          <xs:assert test="every $e in subsequence(xsl:sort, 2) satisfies empty($e/@stable)">
            <xs:annotation>
              <xs:documentation>
                <p>It is a static error if an xsl:sort element other than the first in a 
                  sequence of sibling xsl:sort elements has a stable attribute.
                </p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
          <xs:assert test="count((@group-by, @group-adjacent, @group-starting-with, @group-ending-with)) = 1">
            <xs:annotation>
              <xs:documentation>
                <p>These four attributes are mutually exclusive: it is a static error 
                  if none of these four attributes is present or if more than one of them is present.
                </p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
          <xs:assert test="if (exists(@collation) or exists(@composite)) then (exists(@group-by) or exists(@group-adjacent)) else true()">
            <xs:annotation>
              <xs:documentation>
                <p>It is an error to specify the collation attribute or the composite attribute 
                  if neither the group-by attribute nor group-adjacent attribute is specified.
                </p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
          <xs:assert test="if (exists(@bind-grouping-key)) then (exists(@group-by) or exists(@group-adjacent)) else true()">
            <xs:annotation>
              <xs:documentation>
                <p>It is a static error if the bind-grouping-key attribute is present on an 
                  xsl:for-each-group instruction unless either the group-by or group-adjacent attribute is present.    
                </p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="fork" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:versioned-element-type">
          <xs:choice minOccurs="1" maxOccurs="unbounded">
            <xs:element ref="xsl:sequence"/>
            <xs:element ref="xsl:fallback"/>
          </xs:choice>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="function" substitutionGroup="xsl:declaration">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:versioned-element-type">
          <xs:sequence>
            <xs:element ref="xsl:param" minOccurs="0" maxOccurs="unbounded"/>
            <xs:group ref="xsl:sequence-constructor-group" minOccurs="0" maxOccurs="unbounded"/>
          </xs:sequence>
          <xs:attribute name="name" type="xsl:EQName-in-namespace" use="required"/>
          <xs:attribute name="override" type="xsl:yes-or-no" default="yes"/>
          <xs:attribute name="as" type="xsl:sequence-type" default="item()*"/>
          <xs:attribute name="visibility" type="xsl:visibility-type"/>
          <xs:attribute name="override-extension-function" type="xsl:yes-or-no"/>
          <xs:attribute name="identity-sensitive" type="xsl:yes-or-no"/>
          <xs:attribute name="cache" type="xsl:caching-values"/>
          <xs:assert test="every $e in xsl:param satisfies (empty($e/@select) and empty($e/child::node()))">
            <xs:annotation>
              <xs:documentation>
                <p>A parameter for a function must have no default value.</p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
          <xs:assert test="every $e in xsl:param satisfies empty($e/@visibility)">
            <xs:annotation>
              <xs:documentation>
                <p>A parameter for a function must have no <code>visibility</code> attribute.</p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
          <xs:assert test="every $e in xsl:param satisfies empty($e/@required)">
            <xs:annotation>
              <xs:documentation>
                <p>A parameter for a function must have no <code>required</code> attribute.</p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="if" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:sequence-constructor">
          <xs:attribute name="test" type="xsl:expression" use="required"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="import" substitutionGroup="xsl:declaration">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:attribute name="href" type="xs:anyURI" use="required"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="import-schema" substitutionGroup="xsl:declaration">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:sequence>
            <xs:element ref="xs:schema" minOccurs="0" maxOccurs="1"/>
          </xs:sequence>
          <xs:attribute name="namespace" type="xs:anyURI"/>
          <xs:attribute name="schema-location" type="xs:anyURI"/>
          <xs:assert test="not(exists(@schema-location) and exists(xs:schema))">
            <xs:annotation>
              <xs:documentation>
                <p>XTSE0215: It is a static error if an xsl:import-schema element that contains an 
                xs:schema element has a schema-location attribute
                </p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert> 
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="include" substitutionGroup="xsl:declaration">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:attribute name="href" type="xs:anyURI" use="required"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="iterate" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:versioned-element-type">
          <xs:sequence>
            <xs:element ref="xsl:param" minOccurs="0" maxOccurs="unbounded"/>
            <xs:group ref="xsl:sequence-constructor-group" minOccurs="0" maxOccurs="unbounded"/>
            <xs:element ref="xsl:on-completion" minOccurs="0" maxOccurs="1"/>
          </xs:sequence>
          <xs:attribute name="select" type="xsl:expression" use="required"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="key" substitutionGroup="xsl:declaration">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:sequence-constructor">
          <xs:attribute name="name" type="xsl:EQName" use="required"/>
          <xs:attribute name="match" type="xsl:pattern" use="required"/>
          <xs:attribute name="use" type="xsl:expression"/>
          <xs:attribute name="composite" type="xsl:yes-or-no"/>
          <xs:attribute name="collation" type="xs:anyURI"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>
  
  <xs:element name="map" type="xsl:sequence-constructor" substitutionGroup="xsl:instruction"/>
  
  <xs:element name="map-entry" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:sequence-constructor-and-select">
          <xs:attribute name="key" type="xsl:expression" use="required"/>            
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="matching-substring" type="xsl:sequence-constructor"/>

  <xs:element name="merge" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:sequence>
            <xs:element ref="xsl:merge-source" minOccurs="1" maxOccurs="unbounded"/>
            <xs:element ref="xsl:merge-action" minOccurs="1" maxOccurs="1"/>
            <xs:element ref="xsl:fallback" minOccurs="0" maxOccurs="unbounded"/>
          </xs:sequence>
          <xs:attribute name="bind-group" type="xsl:EQName"/>
          <xs:attribute name="bind-key" type="xsl:EQName"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="merge-action" type="xsl:sequence-constructor"/>

  <xs:element name="merge-key" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:versioned-element-type">
          <xs:sequence>
            <xs:group ref="xsl:sequence-constructor-group" minOccurs="0" maxOccurs="unbounded"/>
          </xs:sequence>
          <xs:attribute name="select" type="xsl:expression"/>
          <xs:attribute name="lang" type="xsl:avt"/>
          <xs:attribute name="order" type="xsl:avt"/>
          <xs:attribute name="collation" type="xs:anyURI"/>
          <xs:attribute name="case-order" type="xsl:avt"/>
          <xs:attribute name="data-type" type="xsl:avt"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="merge-source">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:sequence>
            <xs:element ref="xsl:merge-key" minOccurs="1" maxOccurs="unbounded"/>
          </xs:sequence>
          <xs:attribute name="for-each" type="xsl:expression"/>
          <xs:attribute name="select" type="xsl:expression" use="required"/>
          <xs:attribute name="bind-source" type="xsl:EQName"/>
          <xs:attribute name="streamable" type="xsl:yes-or-no"/>
          <xs:attribute name="sort-before-merge" type="xsl:yes-or-no"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="message" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:sequence-constructor">
          <xs:attribute name="select" type="xsl:expression"/>
          <xs:attribute name="terminate" type="xsl:avt" default="no"/>
          <xs:attribute name="error-code" type="xsl:avt"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="mode" substitutionGroup="xsl:declaration">
    <xs:complexType>
      <xs:complexContent mixed="false">
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:sequence>
            <xs:element ref="xsl:context-item" minOccurs="0" maxOccurs="unbounded"/>
          </xs:sequence>
          <xs:attribute name="name" type="xsl:EQName"/>
          <xs:attribute name="streamable" type="xsl:yes-or-no" default="no"/>
          <xs:attribute name="initial" type="xsl:yes-or-no" default="yes"/>
          <xs:attribute name="on-no-match" type="xsl:on-no-match-type" default="shallow-skip"/>
          <xs:attribute name="on-multiple-match" type="xsl:on-multiple-match-type" default="use-last"/>
          <xs:attribute name="warning-on-no-match" type="xsl:yes-or-no"/>
          <xs:attribute name="warning-on-multiple-match" type="xsl:yes-or-no"/>
          <xs:attribute name="typed" type="xsl:typed-type"/>
          <xs:attribute name="visibility">
            <xs:simpleType>
              <xs:restriction base="xsl:visibility-type">
                <xs:enumeration value="public"/>
                <xs:enumeration value="private"/>
                <xs:enumeration value="final"/>
              </xs:restriction>
            </xs:simpleType>
          </xs:attribute>
          <xs:assert test="not(normalize-space(@initial) = 'no' and exists(xsl:context-item))">
            <xs:annotation>
              <xs:documentation>
                <p>It is a static error if an xsl:mode declaration specifying initial="no" 
                  contains an xsl:context-item element.
                </p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert> 
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>


  <xs:element name="namespace" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:sequence-constructor-or-select">
          <xs:attribute name="name" type="xsl:avt" use="required"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="namespace-alias" substitutionGroup="xsl:declaration">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:attribute name="stylesheet-prefix" type="xsl:prefix-or-default" use="required"/>
          <xs:attribute name="result-prefix" type="xsl:prefix-or-default" use="required"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>


  <xs:element name="next-iteration" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:sequence>
            <xs:element ref="xsl:with-param" minOccurs="0" maxOccurs="unbounded"/>
          </xs:sequence>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>


  <xs:element name="next-match" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:choice minOccurs="0" maxOccurs="unbounded">
            <xs:element ref="xsl:with-param"/>
            <xs:element ref="xsl:fallback"/>
          </xs:choice>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="non-matching-substring" type="xsl:sequence-constructor"/>

  <xs:element name="number" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:versioned-element-type">
          <xs:attribute name="value" type="xsl:expression"/>
          <xs:attribute name="select" type="xsl:expression"/>
          <xs:attribute name="level" type="xsl:level" default="single"/>
          <xs:attribute name="count" type="xsl:pattern"/>
          <xs:attribute name="from" type="xsl:pattern"/>
          <xs:attribute name="format" type="xsl:avt" default="1"/>
          <xs:attribute name="lang" type="xsl:avt"/>
          <xs:attribute name="letter-value" type="xsl:avt"/>
          <xs:attribute name="ordinal" type="xsl:avt"/>
          <xs:attribute name="start-at" type="xsl:avt"/>
          <xs:attribute name="grouping-separator" type="xsl:avt"/>
          <xs:attribute name="grouping-size" type="xsl:avt"/>
          <xs:assert test="if (exists(@value)) then empty((@select, @count, @from)) and @level='single' else true()">
            <xs:annotation>
              <xs:documentation>
                <p>It is a static error if the value attribute of xsl:number is present unless the 
                  select, level, count, and from attributes are all absent.
                </p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>         
          </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="on-completion" type="xsl:sequence-constructor-or-select"/>

  <xs:element name="otherwise" type="xsl:sequence-constructor"/>

  <xs:element name="output" substitutionGroup="xsl:declaration">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:generic-element-type">
          <xs:attribute name="name" type="xsl:EQName"/>
          <xs:attribute name="method" type="xsl:method"/>
          <xs:attribute name="byte-order-mark" type="xsl:yes-or-no"/>
          <xs:attribute name="cdata-section-elements" type="xsl:EQNames"/>
          <xs:attribute name="doctype-public" type="xs:string"/>
          <xs:attribute name="doctype-system" type="xs:string"/>
          <xs:attribute name="encoding" type="xs:string"/>
          <xs:attribute name="escape-uri-attributes" type="xsl:yes-or-no"/>
          <xs:attribute name="html-version" type="xs:decimal"/>
          <xs:attribute name="include-content-type" type="xsl:yes-or-no"/>
          <xs:attribute name="indent" type="xsl:yes-or-no"/>
          <xs:attribute name="item-separator" type="xs:string"/>
          <xs:attribute name="media-type" type="xs:string"/>
          <xs:attribute name="normalization-form" type="xs:NMTOKEN"/>
          <xs:attribute name="omit-xml-declaration" type="xsl:yes-or-no"/>
          <xs:attribute name="parameter-document" type="xs:anyURI"/>
          <xs:attribute name="standalone" type="xsl:yes-or-no-or-omit"/>
          <xs:attribute name="suppress-indentation" type="xsl:EQNames"/>
          <xs:attribute name="undeclare-prefixes" type="xsl:yes-or-no"/>
          <xs:attribute name="use-character-maps" type="xsl:EQNames"/>
          <xs:attribute name="version" type="xs:NMTOKEN"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="output-character">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:attribute name="character" type="xsl:char" use="required"/>
          <xs:attribute name="string" type="xs:string" use="required"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>
  
  <xs:element name="override">
    <xs:annotation>
        <xs:documentation>
            <p>This element appears as a child of <code>xsl:use-package</code> and defines 
            any overriding definitions of components that the containing package wishes to make 
            to the components made available from a library package.</p>
        </xs:documentation>
    </xs:annotation>
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:choice minOccurs="0" maxOccurs="unbounded">
            <xs:element ref="xsl:template"/>
            <xs:element ref="xsl:function"/>
            <xs:element ref="xsl:variable"/>
            <xs:element ref="xsl:param"/>
            <xs:element ref="xsl:attribute-set"/>
          </xs:choice>          
          <xs:assert test="every $e in * satisfies exists($e/@name)">
            <xs:annotation>
              <xs:documentation>
                <p>Every component that is overridden (in particular, templates) must have a <code>name</code> attribute</p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
          <xs:assert test="every $e in xsl:template satisfies empty($e/@match)">
            <xs:annotation>
              <xs:documentation>
                <p>A template that is overridden must not have a <code>match</code> attribute</p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>  
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>   
  </xs:element>
    
  <xs:element name="package">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:sequence>
            <xs:element ref="xsl:use-package" minOccurs="0" maxOccurs="unbounded"/>
            <xs:element ref="xsl:transform" minOccurs="1" maxOccurs="1"/>
            <xs:element ref="xsl:expose" minOccurs="0" maxOccurs="unbounded"/>
          </xs:sequence>
          <xs:attribute name="name" type="xs:anyURI"/>
          <xs:attribute name="package-version" type="xs:string"/>
          <xs:attribute name="input-type-annotations" type="xsl:input-type-annotations-type"/>
          <xs:assert test="every $s in (.//xsl:stylesheet, .//xsl:transform)[@input-type-annotations]
                           satisfies normalize-space($s/@input-type-annotations) = normalize-space(./@input-type-annotations)">
            <xs:annotation>
              <xs:documentation>
                <p>XTSE0265: It is a static error if a stylesheet module specifies the value strip 
                or preserve and the same value is not specified on the xsl:package element 
                of the containing package
                </p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="param" substitutionGroup="xsl:declaration">
    <xs:annotation>
        <xs:documentation>
            <p>Declaration of the <code>xsl:param</code> element, used both defining function
            parameters, template parameters, parameters to <code>xsl:iterate</code>,
            and global stylesheet parameters.</p>
        </xs:documentation>
    </xs:annotation>
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:sequence-constructor-or-select">
          <xs:attribute name="name" type="xsl:EQName" use="required"/>
          <xs:attribute name="as" type="xsl:sequence-type"/>
          <xs:attribute name="required" type="xsl:yes-or-no"/>
          <xs:attribute name="tunnel" type="xsl:yes-or-no"/>
          <xs:attribute name="visibility" type="xsl:visibility-type" use="optional"/>
          <xs:attribute name="static" type="xsl:yes-or-no"/>          
          <xs:assert test="if (normalize-space(@static) = 'yes') 
                           then normalize-space(@visibility) = ('', 'private', 'final') 
                           else true()">
              <xs:annotation>
                <xs:documentation>
                  <p>When the static attribute is present with the value yes, 
                    the visibility attribute must not have a value other than private 
                    or final.</p>
                </xs:documentation>
              </xs:annotation>
            </xs:assert>
          <xs:assert test="if (normalize-space(@static) = 'yes')
                           then empty((*,text())) and exists(@select)
                           else true()">
            <xs:annotation>
              <xs:documentation>
                <p>When the attribute static="yes" is specified, 
                  the xsl:param element must have empty content.</p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert> 
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  

  <xs:element name="perform-sort" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:versioned-element-type">
          <xs:sequence>
            <xs:element ref="xsl:sort" minOccurs="1" maxOccurs="unbounded"/>
            <xs:group ref="xsl:sequence-constructor-group" minOccurs="0" maxOccurs="unbounded"/>
          </xs:sequence>
          <xs:attribute name="select" type="xsl:expression"/>
          <xs:assert test="every $e in subsequence(xsl:sort, 2) satisfies empty($e/@stable)">
            <xs:annotation>
              <xs:documentation>
                <p>It is a static error if an xsl:sort element other than the first in a 
                  sequence of sibling xsl:sort elements has a stable attribute.
                </p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="preserve-space" substitutionGroup="xsl:declaration">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:attribute name="elements" type="xsl:nametests" use="required"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="processing-instruction" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:sequence-constructor-or-select">
          <xs:attribute name="name" type="xsl:avt" use="required"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="result-document" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:sequence-constructor">
          <xs:attribute name="format" type="xsl:avt"/>
          <xs:attribute name="href" type="xsl:avt"/>
          <xs:attribute name="type" type="xsl:EQName"/>
          <xs:attribute name="validation" type="xsl:validation-type"/>
          <xs:attribute name="method" type="xsl:avt"/>
          <xs:attribute name="byte-order-mark" type="xsl:avt"/>
          <xs:attribute name="cdata-section-elements" type="xsl:avt"/>
          <xs:attribute name="doctype-public" type="xsl:avt"/>
          <xs:attribute name="doctype-system" type="xsl:avt"/>
          <xs:attribute name="encoding" type="xsl:avt"/>
          <xs:attribute name="escape-uri-attributes" type="xsl:avt"/>
          <xs:attribute name="html-version" type="xsl:avt"/>
          <xs:attribute name="include-content-type" type="xsl:avt"/>
          <xs:attribute name="indent" type="xsl:avt"/>
          <xs:attribute name="item-separator" type="xsl:avt"/>
          <xs:attribute name="media-type" type="xsl:avt"/>
          <xs:attribute name="normalization-form" type="xsl:avt"/>
          <xs:attribute name="omit-xml-declaration" type="xsl:avt"/>
          <xs:attribute name="parameter-document" type="xsl:avt"/>
          <xs:attribute name="standalone" type="xsl:avt"/>
          <xs:attribute name="suppress-indentation" type="xsl:avt"/>
          <xs:attribute name="undeclare-prefixes" type="xsl:avt"/>
          <xs:attribute name="use-character-maps" type="xsl:EQNames"/>
          <xs:attribute name="output-version" type="xsl:avt"/>
          <xs:assert test="not(exists(@type) and exists(@validation))">
            <xs:annotation>
              <xs:documentation>
                <p>The <code>type</code> and <code>validation</code> attributes are mutually exclusive
                  (if one is present, the other must be absent).</p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>
  
  <xs:element name="sequence" substitutionGroup="xsl:instruction" type="xsl:sequence-constructor-or-select"/>

  <xs:element name="sort">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:sequence-constructor-or-select">
          <xs:attribute name="lang" type="xsl:avt"/>
          <xs:attribute name="data-type" type="xsl:avt" default="text"/>
          <xs:attribute name="order" type="xsl:avt" default="ascending"/>
          <xs:attribute name="case-order" type="xsl:avt"/>
          <xs:attribute name="collation" type="xsl:avt"/>
          <xs:attribute name="stable" type="xsl:avt"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="strip-space" substitutionGroup="xsl:declaration">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:attribute name="elements" type="xsl:nametests" use="required"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="stylesheet" substitutionGroup="xsl:transform"/>

  <xs:element name="stream" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:sequence-constructor">
          <xs:attribute name="href" type="xsl:avt" use="required"/>
          <xs:attribute name="type" type="xsl:EQName"/>
          <xs:attribute name="validation" type="xsl:validation-type"/>
          <xs:assert test="not(exists(@type) and exists(@validation))">
            <xs:annotation>
              <xs:documentation>
                <p>The <code>type</code> and <code>validation</code> attributes are mutually exclusive
                  (if one is present, the other must be absent).</p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="template" substitutionGroup="xsl:declaration">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:versioned-element-type">
          <xs:sequence>
            <xs:element ref="xsl:context-item" minOccurs="0" maxOccurs="1"/>
            <xs:element ref="xsl:param" minOccurs="0" maxOccurs="unbounded"/>
            <xs:group ref="xsl:sequence-constructor-group" minOccurs="0" maxOccurs="unbounded"/>
          </xs:sequence>
          <xs:attribute name="match" type="xsl:pattern"/>
          <xs:attribute name="priority" type="xs:decimal"/>
          <xs:attribute name="mode" type="xsl:modes"/>
          <xs:attribute name="name" type="xsl:EQName"/>
          <xs:attribute name="as" type="xsl:sequence-type" default="item()*"/>
          <xs:attribute name="visibility" type="xsl:visibility-type"/>
          <xs:assert test="exists(@match) or exists(@name)">
            <xs:annotation>
              <xs:documentation>
                <p>An xsl:template element must have either a match attribute or a name attribute, or both.</p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
          <xs:assert test="if (empty(@match)) then (empty(@mode) and empty(@priority)) else true()">
            <xs:annotation>
              <xs:documentation>
                <p>An xsl:template element that has no match attribute must have no mode attribute and no priority attribute.</p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
          <xs:assert test="not(exists(@visibility) and empty(@name))">
            <xs:annotation>
              <xs:documentation>
                <p>An xsl:template element that has no name attribute must have no visibility attribute</p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
          <xs:assert test="if (normalize-space(@visibility) = 'abstract') then empty(* except (xsl:context-item, xsl:param)) else true()">
            <xs:annotation>
              <xs:documentation>
                <p>If the visibility attribute is present with the value abstract then (a) the sequence constructor defining 
                  the template body must be empty: that is, the only permitted children are xsl:context-item and xsl:param</p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
          <xs:assert test="not(normalize-space(@visibility) = 'abstract' and exists(@match))">
            <xs:annotation>
              <xs:documentation>
                <p>If the visibility attribute is present with the value abstract then there must be no match attribute.</p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
          <xs:assert test="every $e in xsl:param satisfies empty($e/@visibility)">
            <xs:annotation>
              <xs:documentation>
                <p>A parameter for a template must have no <code>visibility</code> attribute.</p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:complexType name="text-element-base-type">
    <xs:simpleContent>
      <xs:restriction base="xsl:versioned-element-type">
        <xs:simpleType>
          <xs:restriction base="xs:string"/>
        </xs:simpleType>
        <xs:anyAttribute namespace="##other" processContents="lax"/>
      </xs:restriction>
    </xs:simpleContent>
  </xs:complexType>

  <!--* first cut (for reference)
<xs:element name="text" substitutionGroup="xsl:instruction">
  <xs:complexType>
    <xs:simpleContent>
      <xs:extension base="xsl:text-element-base-type">
        <xs:attribute name="disable-output-escaping" type="xsl:yes-or-no" default="no"/>
      </xs:extension>
    </xs:simpleContent>
  </xs:complexType>
</xs:element>
*-->

  <xs:complexType name="text-element-type">
    <xs:simpleContent>
      <xs:extension base="xsl:text-element-base-type">
        <xs:attribute name="disable-output-escaping" type="xsl:yes-or-no" default="no"/>
      </xs:extension>
    </xs:simpleContent>
  </xs:complexType>

  <xs:element name="text" substitutionGroup="xsl:instruction" type="xsl:text-element-type"/>


  <xs:complexType name="transform-element-base-type">
    <xs:complexContent>
      <xs:restriction base="xsl:element-only-versioned-element-type">
        <xs:attribute name="version" type="xs:decimal" use="optional">
          <xs:annotation>
            <xs:documentation>
              <p>The version attribute indicates the version of XSLT that 
                the stylesheet module requires. The attribute is required, 
                unless the xsl:stylesheet element is a child of an xsl:package 
                element, in which case it is optional: the default is then 
                taken from the parent xsl:package element.</p>
            </xs:documentation>
          </xs:annotation>
        </xs:attribute>
        <xs:anyAttribute namespace="##other" processContents="lax"/>
      </xs:restriction>
    </xs:complexContent>
  </xs:complexType>

  <xs:element name="transform">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="xsl:transform-element-base-type">
          <xs:sequence>
            <xs:choice minOccurs="0" maxOccurs="unbounded">
              <xs:element ref="xsl:declaration"/>
              <xs:any namespace="##other" processContents="lax"/>
              <!-- weaker than XSLT 1.0 -->
            </xs:choice>
          </xs:sequence>
          <xs:attribute name="id" type="xs:ID"/>
          <xs:attribute name="input-type-annotations" type="xsl:input-type-annotations-type"
            default="unspecified"/>
          <!--* The 'static' attribute may be used on 'param' and 'variable'
              * only when they are top-level elements. *-->
          <xs:assert test="every $v in (.//xsl:param, .//xsl:variable)[@static]
            satisfies
            $v[parent::xsl:stylesheet or parent::xsl:transform or parent::xsl:override]
            ">
            <xs:annotation>
              <xs:documentation>
                <p>The static attribute must not be present on an xsl:variable or xsl:param 
                  element unless it is a top-level element.</p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="try" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:versioned-element-type">
          <xs:sequence>
            <xs:group ref="xsl:sequence-constructor-group" minOccurs="0" maxOccurs="unbounded"/>
            <xs:element ref="xsl:catch" minOccurs="1" maxOccurs="1"/>
            <xs:choice minOccurs="0" maxOccurs="unbounded">
              <xs:element ref="xsl:catch"/>
              <xs:element ref="xsl:fallback"/>
            </xs:choice>
          </xs:sequence>
          <xs:attribute name="select" type="xsl:expression" use="optional"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>
  
  <xs:element name="use-package">
    <xs:annotation>
        <xs:documentation>
            <p>This element appears as a child of <code>xsl:package</code> and defines a dependency
            of the containing package on another package, identified by URI in the <code>name</code>
            attribute. The <code>package-version</code> attribute indicates which version of the
            library package is required, or may indicate a range of versions.</p>
        </xs:documentation>
    </xs:annotation>
    <xs:complexType>
      <xs:complexContent mixed="false">
        <xs:extension base="xsl:element-only-versioned-element-type">
          <xs:choice minOccurs="0" maxOccurs="unbounded">
            <xs:element ref="xsl:accept"/>
            <xs:element ref="xsl:override"/>
          </xs:choice>
          <xs:attribute name="name" type="xs:anyURI"/>
          <xs:attribute name="package-version" type="xs:string"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="value-of" substitutionGroup="xsl:instruction">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:sequence-constructor-or-select">
          <xs:attribute name="separator" type="xsl:avt"/>
          <xs:attribute name="disable-output-escaping" type="xsl:yes-or-no" default="no"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="variable" substitutionGroup="xsl:declaration xsl:instruction">
    <xs:annotation>
        <xs:documentation>
            <p>Declaration of the <code>xsl:variable</code> element, used both for local
            and global variable bindings.</p>
            <p>This definition takes advantage of the ability in XSD 1.1 for an element
                to belong to more than one substitution group. A global variable
                is a declaration, while a local variable can appear as an instruction
                in a sequence constructor.</p>
        </xs:documentation>
    </xs:annotation>
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:sequence-constructor-or-select">
          <xs:attribute name="name" type="xsl:EQName" use="required"/>
          <xs:attribute name="as" type="xsl:sequence-type" use="optional"/>
          <xs:attribute name="visibility" type="xsl:visibility-type" use="optional"/>
          <xs:attribute name="static" type="xsl:yes-or-no"/>
          <xs:assert test="if (normalize-space(@static) = 'yes') 
                           then normalize-space(@visibility) = ('', 'private', 'final') 
                           else true()">
            <xs:annotation>
              <xs:documentation>
                <p>When the static attribute is present with the value yes, 
                  the visibility attribute must not have a value other than private 
                  or final.</p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>
          <xs:assert test="if (normalize-space(@static) = 'yes')
                           then (empty((*,text())) and @select) 
                           else true()">
            <xs:annotation>
              <xs:documentation>
                <p>When the attribute static="yes" is specified, 
                  the xsl:variable element must have empty content,
                  and the select attribute must be present to 
                  define the value of the variable.
                </p>
              </xs:documentation>
            </xs:annotation>
          </xs:assert>          
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="when">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:sequence-constructor">
          <xs:attribute name="test" type="xsl:expression" use="required"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="with-param">
    <xs:complexType>
      <xs:complexContent mixed="true">
        <xs:extension base="xsl:sequence-constructor-or-select">
          <xs:attribute name="name" type="xsl:EQName" use="required"/>
          <xs:attribute name="as" type="xsl:sequence-type"/>
          <xs:attribute name="tunnel" type="xsl:yes-or-no"/>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>

  <!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
  <xs:annotation>
    <xs:documentation> PART C: definition of literal result elements There are three ways to define
      the literal result elements permissible in a stylesheet. (a) do nothing. This allows any
      element to be used as a literal result element, provided it is not in the XSLT namespace (b)
      declare all permitted literal result elements as members of the xsl:literal-result-element
      substitution group (c) redefine the model group xsl:result-elements to accommodate all
      permitted literal result elements. Literal result elements are allowed to take certain
      attributes in the XSLT namespace. These are defined in the attribute group
      literal-result-element-attributes, which can be included in the definition of any literal
      result element. </xs:documentation>
  </xs:annotation>
  <!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

  <xs:element name="literal-result-element" abstract="true" type="xs:anyType"/>

  <xs:attributeGroup name="literal-result-element-attributes">
    <xs:attribute name="default-collation" form="qualified" type="xsl:uri-list"/>
    <xs:attribute name="default-mode" type="xsl:default-mode-type"/>
    <xs:attribute name="default-validation" type="xsl:validation-strip-or-preserve"
      default="strip"/>
    <xs:attribute name="expand-text" type="xsl:yes-or-no"/>
    <xs:attribute name="extension-element-prefixes" form="qualified" type="xsl:prefixes"/>
    <xs:attribute name="exclude-result-prefixes" form="qualified" type="xsl:prefixes"/>
    <xs:attribute name="xpath-default-namespace" form="qualified" type="xs:anyURI"/>
    <xs:attribute name="inherit-namespaces" form="qualified" type="xsl:yes-or-no" default="yes"/>
    <xs:attribute name="use-attribute-sets" form="qualified" type="xsl:EQNames" default=""/>
    <xs:attribute name="use-when" form="qualified" type="xsl:expression"/>
    <xs:attribute name="version" form="qualified" type="xs:decimal"/>
    <xs:attribute name="type" form="qualified" type="xsl:EQName"/>
    <xs:attribute name="validation" form="qualified" type="xsl:validation-type"/>
  </xs:attributeGroup>

  <xs:group name="result-elements">
    <xs:choice>
      <xs:element ref="xsl:literal-result-element"/>
      <xs:any namespace="##other" processContents="lax"/>
      <xs:any namespace="##local" processContents="lax"/>
    </xs:choice>
  </xs:group>


  <!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
  <xs:annotation>
    <xs:documentation> PART D: definitions of simple types used in stylesheet attributes
    </xs:documentation>
  </xs:annotation>
  <!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

  <xs:simpleType name="avt">
    <xs:annotation>
      <xs:documentation> This type is used for all attributes that allow an attribute value
        template. The general rules for the syntax of attribute value templates, and the specific
        rules for each such attribute, are described in the XSLT 2.1 Recommendation.
      </xs:documentation>
    </xs:annotation>
    <xs:restriction base="xs:string"/>
  </xs:simpleType>
  
  <xs:simpleType name="caching-values">
    <xs:annotation>
      <xs:documentation> One of the values "full", "partial", or "no". </xs:documentation>
    </xs:annotation>
    <xs:restriction base="xs:token">
      <xs:enumeration value="full"/>
      <xs:enumeration value="partial"/>
      <xs:enumeration value="no"/>
    </xs:restriction>
    
  </xs:simpleType>

  <xs:simpleType name="char">
    <xs:annotation>
      <xs:documentation> A string containing exactly one character. </xs:documentation>
    </xs:annotation>
    <xs:restriction base="xs:string">
      <xs:length value="1"/>
    </xs:restriction>
  </xs:simpleType>
  
   <xs:simpleType name="component-kind-type">
    <xs:annotation>
      <xs:documentation> Describes a kind of component within a package.
      </xs:documentation>
    </xs:annotation>
    <xs:restriction base="xs:token">
      <xs:enumeration value="template"/>
      <xs:enumeration value="function"/>
      <xs:enumeration value="variable"/>
      <xs:enumeration value="attribute-set"/>
      <xs:enumeration value="mode"/>
    </xs:restriction>
  </xs:simpleType>
  
  <xs:simpleType name="default-mode-type">
    <xs:annotation>
      <xs:documentation> The default-mode attribute of xsl:stylesheet, xsl:transform, 
        xsl:package (or any other xsl:* element): either a QName or #unnamed. 
      </xs:documentation>
    </xs:annotation>
    <xs:union memberTypes="xsl:EQName">
      <xs:simpleType>
        <xs:restriction base="xs:token">
          <xs:enumeration value="#unnamed"/>
        </xs:restriction>
      </xs:simpleType>
    </xs:union>
  </xs:simpleType>

  <xs:simpleType name="expression">
    <xs:annotation>
      <xs:documentation> An XPath 2.0 expression. </xs:documentation>
    </xs:annotation>
    <xs:restriction base="xs:token">
      <xs:pattern value=".+"/>
    </xs:restriction>
  </xs:simpleType>

  <xs:simpleType name="item-type">
    <xs:annotation>
      <xs:documentation> An XPath 2.1 ItemType</xs:documentation>
    </xs:annotation>
    <xs:restriction base="xs:token">
      <xs:pattern value=".+"/>
    </xs:restriction>
  </xs:simpleType>

  <xs:simpleType name="input-type-annotations-type">
    <xs:annotation>
      <xs:documentation> Describes how type annotations in source documents are handled.
      </xs:documentation>
    </xs:annotation>
    <xs:restriction base="xs:token">
      <xs:enumeration value="preserve"/>
      <xs:enumeration value="strip"/>
      <xs:enumeration value="unspecified"/>
    </xs:restriction>
  </xs:simpleType>

  <xs:simpleType name="level">
    <xs:annotation>
      <xs:documentation> The level attribute of xsl:number: one of single, multiple, or any.
      </xs:documentation>
    </xs:annotation>
    <xs:restriction base="xs:token">
      <xs:enumeration value="single"/>
      <xs:enumeration value="multiple"/>
      <xs:enumeration value="any"/>
    </xs:restriction>
  </xs:simpleType>

  <xs:simpleType name="mode">
    <xs:annotation>
      <xs:documentation> The mode attribute of xsl:apply-templates: either a QName, or #current, or
        #unnamed, or #default. </xs:documentation>
    </xs:annotation>
    <xs:union memberTypes="xsl:EQName">
      <xs:simpleType>
        <xs:restriction base="xs:token">
          <xs:enumeration value="#default"/>
          <xs:enumeration value="#unnamed"/>
          <xs:enumeration value="#current"/>
        </xs:restriction>
      </xs:simpleType>
    </xs:union>
  </xs:simpleType>

  <xs:simpleType name="modes">
    <xs:annotation>
      <xs:documentation> The mode attribute of xsl:template: either a list, each member being either
        a QName or #default or #unnamed; or the value #all </xs:documentation>
    </xs:annotation>   
      <xs:union>
        <xs:simpleType>
          <xs:restriction>           
            <xs:simpleType>
              <xs:list>
                <xs:simpleType>
                  <xs:union memberTypes="xsl:EQName">
                    <xs:simpleType>
                      <xs:restriction base="xs:token">
                        <xs:enumeration value="#default"/>
                        <xs:enumeration value="#unnamed"/>
                      </xs:restriction>
                    </xs:simpleType>
                  </xs:union>
                </xs:simpleType>
              </xs:list>
            </xs:simpleType>
            <xs:assertion test="count($value) = count(distinct-values($value))">
              <xs:annotation>
                <xs:documentation>
                  <p>XTSE0550: It is a static error if the same token is included more than once in the list.
                  </p>
                </xs:documentation>
              </xs:annotation>
            </xs:assertion>
          </xs:restriction>
        </xs:simpleType>
        <xs:simpleType>
          <xs:restriction base="xs:token">
            <xs:enumeration value="#all"/>
          </xs:restriction>
        </xs:simpleType>
      </xs:union>     
  </xs:simpleType>

  <xs:simpleType name="nametests">
    <xs:annotation>
      <xs:documentation> A list of NameTests, as defined in the XPath 2.0 Recommendation. Each
        NameTest is either a QName, or "*", or "prefix:*", or "*:localname" </xs:documentation>
    </xs:annotation>
    <xs:list>
      <xs:simpleType>
        <xs:union memberTypes="xsl:EQName">
          <xs:simpleType>
            <xs:restriction base="xs:token">
              <xs:enumeration value="*"/>
            </xs:restriction>
          </xs:simpleType>
          <xs:simpleType>
            <xs:restriction base="xs:token">
              <xs:pattern value="\i\c*:\*"/>
              <xs:pattern value="\*:\i\c*"/>
            </xs:restriction>
          </xs:simpleType>
        </xs:union>
      </xs:simpleType>
    </xs:list>
  </xs:simpleType>
  
  <xs:simpleType name="on-multiple-match-type">
    <xs:annotation>
      <xs:documentation> Describes the action to be taken when there are several template rules to match an item in a given mode.
      </xs:documentation>
    </xs:annotation>
    <xs:restriction base="xs:token">
      <xs:enumeration value="use-last"/>
      <xs:enumeration value="fail"/>
    </xs:restriction>
  </xs:simpleType>
  
  <xs:simpleType name="on-no-match-type">
    <xs:annotation>
      <xs:documentation> Describes the action to be taken when there is no template rule to match an item in a given mode.
      </xs:documentation>
    </xs:annotation>
    <xs:restriction base="xs:token">
      <xs:enumeration value="deep-copy"/>
      <xs:enumeration value="shallow-copy"/>
      <xs:enumeration value="deep-skip"/>
      <xs:enumeration value="shallow-skip"/>
      <xs:enumeration value="text-only-copy"/>
      <xs:enumeration value="fail"/>
    </xs:restriction>
  </xs:simpleType>

  <xs:simpleType name="prefixes">
    <xs:list itemType="xs:NCName"/>
  </xs:simpleType>

  <xs:simpleType name="prefix-list-or-all">
    <xs:union memberTypes="xsl:prefix-list">
      <xs:simpleType>
        <xs:restriction base="xs:token">
          <xs:enumeration value="#all"/>
        </xs:restriction>
      </xs:simpleType>
    </xs:union>
  </xs:simpleType>

  <xs:simpleType name="prefix-list">
    <xs:list itemType="xsl:prefix-or-default"/>
  </xs:simpleType>

  <xs:simpleType name="method">
    <xs:annotation>
      <xs:documentation> The method attribute of xsl:output: Either one of the recognized names
        "xml", "xhtml", "html", "text", or a QName that must include a prefix. </xs:documentation>
    </xs:annotation>
    <xs:union>
      <xs:simpleType>
        <xs:restriction base="xs:token">
          <xs:enumeration value="xml"/>
          <xs:enumeration value="xhtml"/>
          <xs:enumeration value="html"/>
          <xs:enumeration value="text"/>
        </xs:restriction>
      </xs:simpleType>
      <xs:simpleType>
        <xs:restriction base="xsl:EQName">
          <xs:pattern value="\c*:\c*"/>
        </xs:restriction>
      </xs:simpleType>
    </xs:union>
  </xs:simpleType>

  <xs:simpleType name="pattern">
    <xs:annotation>
      <xs:documentation> A match pattern as defined in the XSLT 2.1 Recommendation. The syntax for
        patterns is a restricted form of the syntax for XPath 2.0 expressions. Change since XSLT
        2.0: Patterns may now match any item (not only nodes) </xs:documentation>
    </xs:annotation>
    <xs:restriction base="xsl:expression"/>
  </xs:simpleType>

  <xs:simpleType name="prefix-or-default">
    <xs:annotation>
      <xs:documentation> Either a namespace prefix, or #default. Used in the xsl:namespace-alias
        element. </xs:documentation>
    </xs:annotation>
    <xs:union memberTypes="xs:NCName">
      <xs:simpleType>
        <xs:restriction base="xs:token">
          <xs:enumeration value="#default"/>
        </xs:restriction>
      </xs:simpleType>
    </xs:union>
  </xs:simpleType>

  <xs:simpleType name="EQNames">
    <xs:annotation>
      <xs:documentation> A list of QNames. Used in the [xsl:]use-attribute-sets attribute of various
        elements, and in the cdata-section-elements attribute of xsl:output </xs:documentation>
    </xs:annotation>
    <xs:list itemType="xsl:EQName"/>
  </xs:simpleType>

  <xs:simpleType name="EQName">
    <xs:annotation>
      <xs:documentation> 
        <p>An extended QName. This schema does not use the built-in type xs:QName, but rather
        defines its own QName type. This may be either a local name, or a prefixed QName, or a name written
        using the extended QName notation Q{uri}local</p>
        <p>Although xs:QName would define the correct validation on these
        attributes, a schema processor would expand unprefixed QNames incorrectly when constructing
        the PSVI, because (as defined in XML Schema errata) an unprefixed xs:QName is assumed to be
        in the default namespace, which is not the correct assumption for XSLT. The data type is therefore
        defined as a union of NCName and QName, so that an unprefixed name will be validated as an 
        NCName and will therefore not be treated as having the semantics of an unprefixed xs:QName. </p>
      </xs:documentation>
    </xs:annotation>
    <xs:union memberTypes="xs:NCName xs:QName">
      <xs:simpleType>
        <xs:restriction base="xs:token">
          <xs:pattern value="Q\{.*\}\i\c*"/>
        </xs:restriction>
      </xs:simpleType>
    </xs:union>
  </xs:simpleType>
  
  <xs:simpleType name="EQName-in-namespace">
    <xs:annotation>
      <xs:documentation> 
        <p>A subtype of EQNames that excludes no-namespace names</p>
      </xs:documentation>
    </xs:annotation>
        <xs:restriction base="xsl:EQName">
          <xs:pattern value="Q\{.+\}.+|\i\c*:.+"/>
        </xs:restriction>
  </xs:simpleType>  
  
  <xs:simpleType name="sequence-type">
    <xs:annotation>
      <xs:documentation> The description of a data type, conforming to the SequenceType production
        defined in the XPath 2.0 Recommendation </xs:documentation>
    </xs:annotation>
    <xs:restriction base="xs:token">
      <xs:pattern value=".+"/>
    </xs:restriction>
  </xs:simpleType>
  
  <xs:simpleType name="typed-type">
    <xs:annotation>
      <xs:documentation> Describes whether a mode is designed to match typed or untyped nodes.
      </xs:documentation>
    </xs:annotation>
    <xs:restriction base="xs:token">
      <xs:enumeration value="yes"/>
      <xs:enumeration value="no"/>
      <xs:enumeration value="strict"/>
      <xs:enumeration value="lax"/>
      <xs:enumeration value="unspecified"/>
    </xs:restriction>
  </xs:simpleType>

  <xs:simpleType name="uri-list">
    <xs:list itemType="xs:anyURI"/>
  </xs:simpleType>

  <xs:simpleType name="validation-strip-or-preserve">
    <xs:annotation>
      <xs:documentation> Describes different ways of type-annotating an element or attribute.
      </xs:documentation>
    </xs:annotation>
    <xs:restriction base="xsl:validation-type">
      <xs:enumeration value="preserve"/>
      <xs:enumeration value="strip"/>
    </xs:restriction>
  </xs:simpleType>

  <xs:simpleType name="validation-type">
    <xs:annotation>
      <xs:documentation> Describes different ways of type-annotating an element or attribute.
      </xs:documentation>
    </xs:annotation>
    <xs:restriction base="xs:token">
      <xs:enumeration value="strict"/>
      <xs:enumeration value="lax"/>
      <xs:enumeration value="preserve"/>
      <xs:enumeration value="strip"/>
    </xs:restriction>
  </xs:simpleType>
  
  <xs:simpleType name="visibility-type">
    <xs:annotation>
      <xs:documentation> Describes the visibility of a component within a package.
      </xs:documentation>
    </xs:annotation>
    <xs:restriction base="xs:token">
      <xs:enumeration value="public"/>
      <xs:enumeration value="private"/>
      <xs:enumeration value="final"/>
      <xs:enumeration value="abstract"/>
      <xs:enumeration value="hidden"/>
    </xs:restriction>
  </xs:simpleType>
  
  <xs:simpleType name="visibility-not-hidden-type">
    <xs:annotation>
      <xs:documentation> Describes the visibility of a component within a package.
      </xs:documentation>
    </xs:annotation>
    <xs:restriction base="xsl:visibility-type">
      <xs:enumeration value="public"/>
      <xs:enumeration value="private"/>
      <xs:enumeration value="final"/>
      <xs:enumeration value="abstract"/>
    </xs:restriction>
  </xs:simpleType>

  <xs:simpleType name="yes-or-no">
    <xs:annotation>
      <xs:documentation> One of the values "yes" or "no". </xs:documentation>
    </xs:annotation>
    <xs:restriction base="xs:token">
      <xs:enumeration value="yes"/>
      <xs:enumeration value="no"/>
    </xs:restriction>
  </xs:simpleType>

  <xs:simpleType name="yes-or-no-or-omit">
    <xs:annotation>
      <xs:documentation> One of the values "yes" or "no" or "omit". </xs:documentation>
    </xs:annotation>
    <xs:restriction base="xs:token">
      <xs:enumeration value="yes"/>
      <xs:enumeration value="no"/>
      <xs:enumeration value="omit"/>
    </xs:restriction>
  </xs:simpleType>
  
  <xs:simpleType name="zero-digit">
    <xs:annotation>
      <xs:documentation> A digit that has the numerical value zero. </xs:documentation>
    </xs:annotation>
    <xs:restriction base="xsl:char">
      <xs:pattern value="\p{Nd}"/>
      <xs:assertion test="matches(string-join(codepoints-to-string(for $i in 0 to 9 
                          return string-to-codepoints($value) + $i), ''), '\p{Nd}{10}')"/>
    </xs:restriction>
  </xs:simpleType>

</xs:schema>

I Acknowledgements (Non-Normative)

This specification was developed and approved for publication by the W3C XSL Working Group (WG). WG approval of this specification does not necessarily imply that all WG members voted for its approval.

The chair of the XSL WG is Sharon Adler. The active membership of the XSL WG at the time of publication comprises:

Sharon Adler (Chair)
Anders Berglund
Oliver Becker
Carine Bournez (W3C team)
Abel Braaksma
Florent Georges
Michael Kay (Editor)
Jirka Kosek
Michael Sperberg-McQueen
Mohamed Zergaoui

The Working Group wishes to acknowledge the contribution of those who have participated in the work at earlier stages, as well as the pioneering work of the developers of STX (see [STX]) which has formed an important intellectual input to the design of XSLT 3.0 and has demonstrated the feasibility of creating a streaming transformation language based on the core XSLT concept of recursive descent of the source tree using rule-based templates.

J Changes since XSLT 2.0 (Non-Normative)

J.1 Changes in this Specification

  1. A stylesheet may now consist of multiple packages. The language specification for packages has been designed with a view to allowing packages to be compiled independently of each other. The specification provides control over the interface offered by a package to other packages; in particular it allows functions, variables, named templates and other components to be declared as public, private, final, or abstract.

  2. A new xsl:mode declaration is added.

    1. A mode may be declared to be streamable, and rules are given that constrain what the template rules in a streamable mode can do.

    2. The xsl:mode declaration may contain an xsl:context-item element to declare the expected type of the initial context item when this mode is the initial mode.

    3. An xsl:mode declaration may define the action to be taken when there is no matching template rule, and the action to be taken when there are multiple matching template rules.

    4. An xsl:mode declaration may indicate that the template rules in a given mode are designed to process typed (schema-validated) nodes only, or untyped nodes only. It may also indicate that element names appearing in match patterns for the mode are only to match elements in the source document that have been validated against the corresponding element declarations in the schema.

    5. A default mode can be declared for a stylesheet module, making it easier to reuse existing stylesheet modules to construct a composite stylesheet.

  3. Several new instructions are introduced with the aim of making it easier to write streamable transformations, although most of these instructions can also be used without streaming:

    1. The xsl:stream instruction is provided specifically to read and process an input document using streaming.

    2. The xsl:iterate instruction allows iterative processing of a sequence, with the ability for the processing of one item to depend on the results of processing of previous items, and with the ability to terminate the iteration before all the items in the sequence have been processed.

    3. The xsl:merge instruction allows several input sequences to be merged into a single output sequence, based on the value of a merge key.

    4. The xsl:fork instruction allows multiple results to be computed during a single pass of a streamed input document.

      The xsl:sequence instruction can now contain a sequence constructor as an alternative to using the select attribute. This is primarily for use cases involving xsl:fork.

  4. Other changes introduced to facilitate the writing of streamable stylesheets include:

    1. The new top-level declaration xsl:accumulator is introduced. An accumulator represents information about a node in a document that can be computed during a streamed pass over the document, starting at the start and ending at that node.

    2. An [xsl:]on-empty attribute is provided for xsl:element, xsl:copy, xsl:attribute, and literal result elements, to control their behavior when the content of the constructed node would otherwise be empty.

    3. New functions copy-of and snapshot are provided, to enable streaming applications to operate in "windowing" mode, where the input document is divided into a sequence of small subtrees processed one at a time.

  5. Some further new instructions are provided, unrelated to streaming:

    1. The xsl:try instruction allows recovery from dynamic errors.

    2. A new xsl:evaluate instruction is provided, to allow evaluation of XPath expressions constructed dynamically from strings, or read from a source document.

    3. The xsl:assert instruction allows arbitrary assertions about the state of variables or the input document, improving testability and robustness.

  6. Text nodes within a sequence constructor may now contain text value templates (XPath expressions enclosed in curly brackets), if this is enabled by setting expand-text="yes"> on an enclosing element.

  7. The syntax of patterns has been generalized. Patterns may now match any item (not only nodes). In consequence, xsl:apply-templates can now process sequences of atomic values as well as nodes, and xsl:for-each-group with the group-starting-with and group-ending-with options can also process atomic sequences. As a further consequence, the initial context item supplied when initiating a transformation is no longer required to be a node.

  8. A new datatype, called a map, has been introduced, together with supporting functions, operators, and type syntax. Maps allow more complex data structures to be created than is possible using atomic values and nodes alone. This has particular applications to streamed processing: since a streamed application can visit each node of its primary input document only once, it often needs more advanced data structures to retain what it has already seen in the document.

  9. Miscellaneous changes to existing instructions and declarations include:

    1. The regular expression supplied to the xsl:analyze-string instruction is now permitted to be one that matches a zero-length string.

    2. The xsl:copy instruction now has a select attribute, which is convenient when it is used inside a function where there is no context item.

    3. Composite keys are supported in xsl:for-each-group.

    4. Two new attributes have been added to xsl:function to provide increased scope for optimization: identity-sensitive and cache. The first indicates whether the identity of nodes passed in the arguments or result of the function is significant; the second indicates whether the function is to cache its results (memoization).

    5. The override attribute of xsl:function is renamed override-extension-function, retaining the old name as a deprecated synonym.

    6. The rule requiring xsl:import declarations to precede all other declarations in a stylesheet module has been removed.

    7. Composite keys are supported in xsl:key.

    8. A new attribute on xsl:message allows specification of the error code to be returned with terminate="yes" is specified.

    9. The rules for handling conflicts between xsl:strip-space and xsl:preserve-space have changed. A conflict that can be detected statically is now signaled as a static error; a run-time conflict between two declarations having the same precedence and priority is now resolved by taking whichever comes last in declaration order.

    10. An xsl:template declaration may contain an xsl:context-item element to declare the required type of the context item when the template is called.

    11. An empty xsl:value-of instruction with no select attribute is now permitted; its effect is to construct a zero-length text node.

    12. The xsl:variable and xsl:param elements may now specify static="yes", denoting that the variable is available statically (informally, "at compile time"). Static variables and parameters make the [xsl:]use-when mechanism more useful, especially in conjunction with xsl:assert.

  10. New functions are available to import and export data in JSON format.

  11. A basic XSLT Processor now recognizes all the built-in types defined in XML Schema.

  12. A basic XSLT Processor will now accept the attribute validation="lax" and interpret it in the same way as a schema-aware processor when there is no schema component available to perform the validation.

  13. Some functions, including generate-idFO30, format-dateFO30, format-dateTimeFO30, format-numberFO30, format-timeFO30, and unparsed-textFO30 have been moved from this specification to the core Functions and Operators specification, to make them available in other host languages.

  14. The rule that effectively prevented references to external documents in [xsl:]use-when expressions has been removed.

  15. A default value is defined for the named template to be used when initiating a transformation (specifically, xsl:initial-template).

  16. Serialization to HTML5 and XHTML5 is supported. To this end, a new serialization parameter html-version is provided in xsl:output and xsl:result-document.

  17. The concept of recoverable dynamic errors has been dropped. Of the remaining recoverable dynamic errors, some are no longer errors, and others are now situations where the behavior of the processor is implementation-dependent. The adjective "non-recoverable" in describing other dynamic errors becomes redundant and has therefore been dropped (the term was in any case misleading since the introduction of a try/catch mechanism). Error codes of the form XTREnnnn have been renumbered XTDEnnnn.

    Dynamic errors occurring during pattern evaluation are always masked (they cause the pattern to report a non-match.)

  18. The new serialization parameter html-version is supported in xsl:output and xsl:result-document. Note that the item-separator attribute is not available in XSLT because the value that is serialized by XSLT is always a singleton document node.

  19. A family of collation URIs is defined for selecting collations based on the Unicode Collation Algorithm.

  20. Serialization parameters can now be specified in an external parameter document.

  21. The effect of specifying the type xs:untyped or xs:untypedAtomic when validating by type is now defined.

  22. The xsl:output and xsl:result-document elements now allow a parameter-document attribute allowing serialization to be configured in an external document.

  23. The set of constructs that set temporary output state has been reduced, and no longer includes instructions that create nodes, such as xsl:attribute and xsl:value-of. However, xsl:merge-key has been added to the list.

  24. The possibilities for invocation of a stylesheet have been expanded; they now include the ability to directly execute a stylesheet function; to supply parameters to the initial template; and to return the results of the invoked template or function as a raw value, without construction of a result tree.

J.2 Changes in Other Related Specifications

A number of changes affecting XSLT 2.0 have been made in other related specifications. Some of the more significant changes are as follows:

  1. A number of new functions have been defined whose aim is to facilitate streaming. These include unparsed-text-linesFO30, innermostFO30, outermostFO30.

  2. XPath 3.0 supports a subset of the let expression from XQuery.

  3. XPath 3.0 supports function items as first-class values (functions can, for example, be bound to variables and passed as parameters to other functions.)

  4. XPath 3.0 supports a new syntax for writing expanded names using the namespace URI and local part only, avoiding the need to create a static context that binds namespace prefixes. This is intended to be particularly useful when XPath expressions are software-generated. Complementing this, a new function pathFO30 is available to generate a (namespace-context-independent) path to any node that can subsequently be evaluated using the xsl:evaluate instruction, or otherwise.

K Changes since the Working Draft of 10 July 2012 (Non-Normative)

This section lists all significant changes since the Working Draft published on 10 July 2012.

  1. Text nodes within a sequence constructor may now contain text value templates (XPath expressions enclosed in curly brackets), if this is enabled by setting expand-text="yes"> on an enclosing element.

  2. An empty xsl:value-of instruction with no select attribute is now permitted; its effect is to construct a zero-length text node.

  3. Static variables and parameters are introduced, to make the [xsl:]use-when mechanism more useful, especially in conjunction with xsl:assert.

  4. The rule requiring xsl:import declarations to precede all other declarations in a stylesheet module has been removed.

  5. The rule that effectively prevented references to external documents in [xsl:]use-when expressions has been removed.

  6. The enabled attribute of xsl:assert is removed; its effect can now be achieved more conveniently using a use-when attribute.

  7. A default value is defined for the named template to be used when initiating a transformation (specifically, xsl:initial-template).

  8. The override attribute of xsl:function is renamed override-extension-function, retaining the old name as a deprecated synonym.

  9. The rules for conformance against optional features have been refactored.

  10. (In the July 2012 draft but omitted from the change list): The xsl:sequence instruction can now contain a sequence constructor as an alternative to using the select attribute. This is primarily for use cases involving xsl:fork.

  11. A new attribute with-params is provided on xsl:evaluate, to allow parameters to be computed dynamically in the form of a map. This works alongside the existing mechanism using xsl:with-param children.

  12. The concept of recoverable dynamic errors has been dropped. Of the remaining recoverable dynamic errors, some are no longer errors, and others are now situations where the behavior of the processor is implementation-dependent. The adjective "non-recoverable" in describing other dynamic errors becomes redundant and has therefore been dropped (the term was in any case misleading since the introduction of a try/catch mechanism). Error codes of the form XTREnnnn have been renumbered XTDEnnnn.

  13. The new serialization parameters html-version and item-separator are supported in xsl:output and xsl:result-document.

  14. Two new attributes have been added to xsl:function to provide increased scope for optimization: identity-sensitive and cache.

  15. A family of collation URIs is defined for selecting collations based on the Unicode Collation Algorithm.

  16. The on-empty attribute of xsl:copy is no longer ignored in cases where the selected node is not a document or element node.

  17. Serialization parameters can now be specified in an external parameter document.

  18. The effect of specifying the type xs:untyped or xs:untypedAtomic when validating by type is now defined.

  19. Maps no longer have an associated collation. In its place, a new collation-key function is introduced to allow key values to be normalized according to the rules of a given collation.

  20. The syntax for patterns has been rewritten. The grammar is now closely aligned with the XPath 3.0 grammar, so that it can be readily verified that the grammar is a subset of XPath, and that there are no needless restrictions (this was necessary to fix some bugs in this area). The type-based syntax ~typename used in earlier drafts was found not to be well-aligned with practical use cases for matching atomic values, and has been replaced by the construct .[ Expr ] which tests the item using an arbitrary boolean expression.

  21. Accumulators are now classified as components for the purpose of defining packages; in addition, the rules for overriding them using xsl:import are now defined. The name and initial-value attributes of an accumulator are now mandatory.

  22. The regular expression supplied to the xsl:analyze-string instruction is now permitted to be one that matches a zero-length string.

  23. The xsl:output and xsl:result-document elements now allow a parameter-document attribute allowing serialization to be configured in an external document.

  24. The xsl:evaluate instruction has been made part of an optional feature, the dynamic evaluation feature.

  25. Dynamic errors occurring during pattern evaluation are always masked (they cause the pattern to report a non-match.)

  26. Stylesheet parameters that specify required="yes" must have visibility equal to public.

  27. The meaning of on-no-match="deep-skip" has been changed when the selected node is a document node; in this case it is now equivalent to shallow-skip.

  28. Redundant parentheses at the outermost level of a pattern in a template rule now have no effect on the semantics: they do not affect the default priority, and they do not prevent the branches of a union being effectively treated as separate template rules.

  29. The method for invoking accumulator functions has changed; instead of user-defined functions, there are now two built-in functions accumulator-before and accumulator-after that take the accumulator name as an argument.

  30. The attributes default-collation and default-mode can now be specified on any element.

  31. The attribute initial on xsl:mode is dropped, as the same effect can be achieved using the visibility attribute.

  32. It is now a dynamic error for a map expression or an xsl:map instruction to generate duplicate keys.

  33. There has been a substantial rewrite of section 19 Streamability. Some of the changes are to relax restrictions on streamability that were found to be a nuisance; others are to fix errors in the analysis rules that meant some constructs (such as the copy-of function) could not effectively be used for their intended purpose. Other changes are simply for clarity or conciseness of exposition. The new concept of posture reintroduces (under a different guise) the path analysis that was described in graphical terms in an earlier working draft.

  34. References to ECMA-262 (for the specification of JSON) have been replaced with references to ECMA-404.

  35. Attributes validation and type have been added to the xsl:stream instruction to control schema-validation of streamed input documents.

  36. The process of initiating a stylesheet is revised to allow applications to invoke public functions as well as public template rules, to allow parameters to the initial template or function to be supplied, and to get the "raw result" of invoking a public template or function, without the result being wrapped into a result tree.

  37. The syntax for map expressions has changed to use colon (:) as the separator between key and value, rather than :=.

L Incompatibilities with XSLT 2.0 (Non-Normative)

This section lists all known incompatibilities with XSLT 2.0, that is, situations wher a stylesheet that is error-free according to the XSLT 2.0 specification and where all elements have an effective version of 2.0 or less, will produce different results depending on whether it is run under an XSLT 2.0 processor or an XSLT 3.0 processor.

  1. XSLT 2.0 gave implementations freedom what to do when a node selected by xsl:apply-templates matched more than one template rule. XSLT 3.0 is more prescriptive in this situation. The behavior prescribed in XSLT 3.0 (selecting the template rule that is last in declaration order) is compatible with the action of some XSLT 2.0 processors but not necessarily others.

  2. It is now a static error if the same NameTest appears in both an xsl:strip-space and an xsl:preserve-space declaration with the same precedence and priority. Previously this was a dynamic error, and processors were allowed to recover from the error.

  3. The current group and current grouping key are now absent rather than empty when not in use, which means that attempting to refer to them in this state gives a dynamic error.

  4. As a consequence of functions such as format-dateFO30 moving from this specification to [Functions and Operators], error codes associated with these functions have changed.

  5. The concept of recoverable dynamic errors has been dropped. Of the remaining recoverable dynamic errors, some are no longer errors, and others are now situations where the behavior of the processor is implementation-dependent. Error codes of the form XTREnnnn have been renumbered XTDEnnnn.

  6. In previous versions of the specification, the element-available function when applied to names in the XSLT namespace was defined to return false in the case of XSLT elements other than instructions. (Actual practise in implementations was not always consistent with this rule). In XSLT 3.0 the rules have been changed so that it returns true for the names of such elements, bringing the specification of the function into line with the intuitive meaning of its name.

  7. (This is not strictly speaking an incompatibility, as conforming XSLT 2.0 stylesheets will continue to function correctly without error. It can be considered as migration advice, a warning that care is needed when introducing new XSLT 3.0 features.)

    When a function or template has a parameter with a declared type of item(), it should not assume (as it could in XSLT 2.0) that when the supplied item is not a node, it must be an atomic value, and vice versa. In XSLT 3.0 there is a third option: it might be a function. Functions and templates that fail to cater for this possibility may fail with a type error if the caller supplies a function as the relevant parameter value.