W3C

XSL Transformations (XSLT) Version 2.0

W3C Working Draft 12 November 2003

This version:
http://www.w3.org/TR/2003/WD-xslt20-20031112/
Latest version:
http://www.w3.org/TR/xslt20/
Previous versions:
http://www.w3.org/TR/2003/WD-xslt20-20030502/
http://www.w3.org/TR/2002/WD-xslt20-20021115/
http://www.w3.org/TR/2002/WD-xslt20-20020816/
http://www.w3.org/TR/2002/WD-xslt20-20020430/
http://www.w3.org/TR/2001/WD-xslt20-20011220/
Editor:
Michael Kay, Software AG <Michael.Kay@softwareag.com>

This document is also available in these non-normative formats: HTML without revision markings and HTML with revision markings.


Abstract

This specification defines the syntax and semantics of XSLT 2.0, which is a language for transforming XML documents into other XML documents.

XSLT 2.0 is designed to be used in conjunction with XPath 2.0, which is defined in [XPath 2.0]. XSLT shares the same data model as XPath 2.0, which is defined in [Data Model], and it uses the library of functions and operators defined in [Functions and Operators].

XSLT 2.0 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 XP for XPath, DM for the Data Model, FO for Functions and Operators.

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 specification is a Last Call Working Draft of XSLT 2.0. This is a signal that:

The final date for comments on this draft is 15 February 2004. Comments should be sent to public-qt-comments@w3.org. Because the same mailing list is also used for comments on XPath 2.0 and XQuery 1.0, it is helpful to include the string [XSLT2.0] in the subject line, together with an originator's reference number that can be used to track progress in dealing with the comment. If possible, please send each comment as a separate email. Archives of the comments and responses are available.

The document is published in two versions: one that highlights changes since the previous published Working Draft, and one without change highlighting.

As predicted in the previous (May 2003) draft, there are relatively few technical innovations in this draft, but a substantial amount of editorial revision and clarification. The technical changes of note are the ability of many XSLT instructions (for example, xsl:attribute and xsl:value-of) to use a select attribute or a contained sequence constructor interchangeably, and the introduction of tunnel parameters which allow parameter values to be passed from a high-level template rule to a low-level rule without being declared in all the intermediate templates. Named sort keys and the sort function have been replaced with a new xsl:perform-sort instruction. There have been revisions to the date formatting functions, aligning them with the xsl:number instruction and transferring some of the functionality into xsl:number to make it more widely applicable.

A detailed summary of the changes is included at K.2.4 Changes since the May 2003 draft

The Working Group has commenced, but has not yet completed, a review of the classification of all error conditions described in this draft. It is likely that this review will cause the classification of some errors to change, for example some errors currently classified as recoverable may change to being non-recoverable, or vice versa. Comments on the classification, or on the general approach to handling of dynamic errors, are welcomed.

The statements in this draft concerning dependencies on other specifications that are not yet Recommendations (notably XML 1.1 and XML Namespaces 1.1) must be regarded as provisional, pending final acceptance of those specifications.

Publication as a 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.

XSLT 2.0 is a revised version of the XSLT 1.0 Recommendation [XSLT 1.0] published on 16 November 1999. The changes made in this document are intended to meet the requirements for XSLT 2.0 described in [XSLT 2.0 Requirements] and to incorporate fixes for errors that have been detected in XSLT 1.0. A summary of the changes since XSLT 1.0 is included in K Changes from XSLT 1.0.

XSLT 2.0 is designed to be used together with XPath 2.0, which has been developed by the W3C XSL Working Group in collaboration with the XML Query Working Group. The current specification of XPath 2.0 can be found in [XPath 2.0].

Public discussion of XSL, including XSL Transformations, takes place on the XSL-List mailing list.

The English version of this specification is the only normative version. However, for translations of this document, see http://www.w3.org/Style/XSL/translations.html.

The development of XSLT is undertaken by the XSL Working Group which is now part of the W3C XML Activity.

Patent disclosures relevant to this specification may be found on the XSL Working Group's patent disclosure page at http://www.w3.org/Style/XSL/Disclosures.html.

Table of Contents

1 Introduction
    1.1 What is XSLT?
    1.2 What's new in XSLT 2.0?
2 Concepts
    2.1 Terminology
    2.2 Notation
    2.3 Initiating a Transformation
    2.4 Executing a Transformation
    2.5 The Stylesheet Evaluation Context
        2.5.1 Maintaining Position: the Focus
        2.5.2 Additional Context Variables
    2.6 Parsing and Serialization
    2.7 Extensibility
    2.8 Stylesheets and Schemas
    2.9 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 Stylesheet Element
        3.6.1 User-defined Data Elements
    3.7 Simplified Stylesheet Modules
    3.8 Backwards-Compatible Processing
    3.9 Forwards-Compatible Processing
    3.10 Combining Stylesheet Modules
        3.10.1 Locating Stylesheet Modules
        3.10.2 Stylesheet Inclusion
        3.10.3 Stylesheet Import
    3.11 Embedded Stylesheet Modules
    3.12 Built-in Types
    3.13 Importing Schema Components
4 Data Model
    4.1 XML Versions
    4.2 Stripping Whitespace from the Stylesheet
    4.3 Stripping Whitespace from a Source Tree
    4.4 Attributes Types and DTD Validation
    4.5 Disable Output Escaping
5 Syntactic Constructs
    5.1 Qualified Names
    5.2 Unprefixed QNames in Expressions and Patterns
    5.3 Expressions
        5.3.1 Initializing the Static Context
        5.3.2 Initializing the Dynamic Context
    5.4 Patterns
    5.5 Attribute Value Templates
    5.6 Sequence Constructors
        5.6.1 Constructing Complex Content
        5.6.2 Constructing Simple Content
        5.6.3 Namespace Fixup
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 Modes
    6.6 Built-in Template Rules
    6.7 Overriding Template Rules
7 Repetition
8 Conditional Processing
    8.1 Conditional Processing with xsl:if
    8.2 Conditional Processing with xsl:choose
9 Variables and Parameters
    9.1 Variables
    9.2 Parameters
    9.3 Values of Variables and Parameters
    9.4 Temporary Trees
    9.5 Global Variables and Parameters
    9.6 Local Variables and Parameters
    9.7 Scope of Variables
    9.8 Circular Definitions
10 Callable Components
    10.1 Named Templates
        10.1.1 Passing Parameters to Templates
        10.1.2 Tunnel Parameters
    10.2 Named Attribute Sets
    10.3 Stylesheet Functions
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 Namespace Aliasing
    11.2 Creating Element Nodes using xsl:element
        11.2.1 Setting the Type Annotation for a Constructed Element Node
    11.3 Creating Attribute Nodes using xsl:attribute
        11.3.1 Setting the Type Annotation for a Constructed Attribute Node
    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 Processing Instructions
    11.6 Creating Namespace Nodes
    11.7 Creating Comments
    11.8 Copying Nodes from a Source Tree to a Result Tree
        11.8.1 Shallow Copy
        11.8.2 Deep Copy
    11.9 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
14 Grouping
    14.1 The Current Group
    14.2 The Current Grouping Key
    14.3 The xsl:for-each-group Element
    14.4 Examples of Grouping
15 Regular Expressions
    15.1 The xsl:analyze-string instruction
    15.2 Captured Substrings
    15.3 Examples of Regular Expression Matching
16 Additional Functions
    16.1 Multiple Source Documents
    16.2 Reading Text Files
    16.3 Keys
        16.3.1 The xsl:key Declaration
        16.3.2 The key Function
    16.4 Number Formatting
        16.4.1 Defining a Decimal Format
        16.4.2 Processing the Picture String
        16.4.3 Analysing the Picture String
        16.4.4 Formatting the Number
    16.5 Formatting Dates and Times
        16.5.1 The Picture String
        16.5.2 The language, calendar, and country arguments
        16.5.3 Examples of date and time formatting
    16.6 Miscellaneous Additional Functions
        16.6.1 current
        16.6.2 unparsed-entity-uri
        16.6.3 unparsed-entity-public-id
        16.6.4 generate-id
        16.6.5 system-property
17 Messages
18 Extensibility and Fallback
    18.1 Extension Functions
        18.1.1 Testing Availability of Functions
        18.1.2 Calling Extension Functions
        18.1.3 External Objects
    18.2 Extension Instructions
        18.2.1 Designating an Extension Namespace
        18.2.2 Testing Availability of Instructions
        18.2.3 Fallback
19 Result Trees
    19.1 Creating Result Trees
    19.2 Validation
        19.2.1 Validating Constructed Elements and Attributes
        19.2.2 Validating Document Nodes
20 Serialization
    20.1 Character Maps
    20.2 Disabling Output Escaping
21 Conformance
    21.1 Basic XSLT Processor
    21.2 Schema-Aware XSLT Processor
    21.3 Serialization Feature
    21.4 Backwards Compatibility Feature

Appendices

A References
    A.1 Normative References
    A.2 Other References
B The XSLT Media Type
    B.1 Registration of MIME media type application/xslt+xml
    B.2 Fragment Identifiers
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 Schema for XSLT Stylesheets (Non-Normative)
H Acknowledgements (Non-Normative)
I Checklist of Requirements (Non-Normative)
J Summary of Issues (Non-Normative)
    J.1 Open Issues
    J.2 Decided Issues
    J.3 Closed Issues
K Changes from XSLT 1.0 (Non-Normative)
    K.1 Incompatible Changes
        K.1.1 Backwards Compatibility Behavior
        K.1.2 Incompatibility in the Absence of a Schema
        K.1.3 Compatibility in the Presence of a Schema
        K.1.4 XPath 2.0 Backwards Compatibility
    K.2 New Functionality
        K.2.1 Pervasive changes
        K.2.2 Major Features
        K.2.3 Minor Changes
        K.2.4 Changes since the May 2003 draft


1 Introduction

1.1 What is XSLT?

This specification defines the syntax and semantics of the XSLT 2.0 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 [XML Namespaces 1.0].]

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]), or into another presentation-oriented format such as HTML, XHTML, or SVG. However, XSLT is used for a wide range of XML-to-XML transformation tasks, not exclusively for formatting and presentation applications.

A transformation expressed in XSLT describes rules for transforming one 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, which can be evaluated 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.

[Definition: A stylesheet may consist of several stylesheet modules, contained in different XML documents. For a given transformation, one of these 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 3.10.2 Stylesheet Inclusion and 3.10.3 Stylesheet Import.]

1.2 What's new in XSLT 2.0?

XSLT 1.0 was published in November 1999, and version 2.0 represents a significant increase in the capability of the language. A detailed list of changes is included in K Changes from XSLT 1.0. XSLT 2.0 has been developed in parallel with XPath 2.0 (see [XPath 2.0]), so the changes to XPath must be considered alongside the changes to XSLT.

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 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 ].

Note:

The precise meanings of the terms source tree and result tree, as used in this specification, depend on the context. In the context of the stylesheet as a whole, the source trees are the trees provided as the initial input to the transformation, together with any trees supplied as stylesheet parameters and any trees accessed using the document, doc FO or collection FO functions; while the result trees are the trees created by an explicit xsl:result-document instruction as well as the implicit result tree created in the absence of an xsl:result-document instruction. In the context of an individual instruction in the stylesheet, the term source tree also includes any temporary tree that the instruction is using for input, and the term result tree includes any temporary tree that the instruction is using for output.

In this specification the words must, must not, should, should not, may, required, and recommended are to be interpreted as described in [RFC2119]. Where the word must 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 21 Conformance. Where the word must relates to a stylesheet, then the processor must enforce this constraint on stylesheets.

[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 should be described in the vendor's documentation.]

[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 2.0] or the Data Model specification [Data Model]. Particular attention is drawn to the following:

  • [Definition: The term atomization is defined in Section 2.3.2 AtomizationXP. It is a process that takes as input a sequence of nodes and atomic values, and returns a sequence of atomic values, in which the nodes are replaced by their typed values as defined in [Data Model].] For some nodes (for example, elements with element-only content), atomization generates a dynamic error.

  • [Definition: The term typed value is defined in Section 5.6 typed-value AccessorDM. Every node except an element defined in the schema with 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 5.5 string-value AccessorDM. 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 ContextXP. 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 2.0 and XPath 1.0.]

2.2 Notation

In this document the specification of each XSLT-defined element type 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.

  • 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.

    In all cases where this specification states that the value of an attribute must be one of a limited set of values, 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 XT0010] A static error is signaled 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.

Special rules apply if the construct appears in part of the stylesheet that is processed with forwards-compatible behavior: see 3.9 Forwards-Compatible Processing.

Note:

This working draft includes a non-normative XML Schema for XSLT stylesheet modules (see G 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]. The signatures of these functions are described using the same notation as used in [Functions and Operators]. The names of these functions are all 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 must be supplied when a transformation is initiated.

Implementations may allow a transformation to run as two or more phases, for example parsing, compilation and execution. Such a distinction is outside the scope of this specification, which treats transformation as a single process controlled using a set of stylesheet modules, supplied in the form of XML documents.

The following information is supplied to execute a transformation:

[ERR XT0040] It is a non-recoverable 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.

[ERR XT0050] It is a non-recoverable dynamic error if the stylesheet that is invoked declares a visible stylesheet parameter with required="yes" and no value for this parameter is supplied during the invocation of the stylesheet. A stylesheet parameter is visible if it is not masked by another global variable or parameter with the same name and higher import precedence.

[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 node in the initial mode.]

Parameters passed to the transformation by the client application are matched against stylesheet parameters (see 9.5 Global Variables and Parameters), not against the template parameters declared within the initial template. All template parameters within the initial template to be executed will take their default values.

[ERR XT0060] It is a non-recoverable dynamic error if the initial template defines a template parameter that specifies required="yes".

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 16.1 Multiple Source Documents) or doc FO or collection FO (see [Functions and Operators]), or they can be supplied as stylesheet parameters (see 9.5 Global Variables and Parameters), or as the result of an extension function (see 18.1 Extension Functions).

2.4 Executing a Transformation

[Definition: A stylesheet contains a set of template rules (see 6 Template Rules). A template rule has two parts: a pattern that is matched against nodes, and a sequence constructor that is evaluated to produce a sequence of items. In most cases these items are 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 5.6 Sequence Constructors. If the result is a non-empty sequence, then this sequence is used to construct an implicit result tree, following the rules described in 5.6.1 Constructing Complex Content: the effect is as if the sequence constructor contained in the initial template were contained in an xsl:result-document element with no attributes.

[Definition: The elements appearing within a sequence constructor are referred to as instructions.]

The main categories of instruction elements 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 the source tree.

2.5 The Stylesheet Evaluation Context

During the evaluation of a stylesheet, certain information is maintained about the current state of processing. This information is referred to collectively as the evaluation context. The variables that make up the evaluation context are described in this section.

The evaluation context is structured as a stack. When an instruction is evaluated, it inherits the state of the evaluation context from its calling instruction. An instruction may make modifications to the state of the evaluation context, but on return to its caller, the evaluation context is always in the same state as it was on entry to the instruction. The scope of variables in the evaluation context is dynamic; they are passed implicitly from a calling template to a called template, except where otherwise specified.

The variables making up the evaluation context are not available when a stylesheet function is called from an XPath expression. On entry to a stylesheet function, a new empty evaluation context is established. Some variables in an empty evaluation context are said to be undefined, in which case any reference to this variable causes a dynamic error. Other variables are initialized to a defined value, such as an empty sequence.

For convenience, the evaluation 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.

2.5.1 Maintaining Position: the Focus

[Definition: When a sequence constructor is evaluated, the processor keeps track of which nodes 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), or a node. The context item is initially set to the initial context node 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, 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.

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 16.6.1 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 undefined. The focus is also undefined on initial entry to the stylesheet if no initial context node supplied.

[ERR XT0070] When the focus is undefined, evaluation of any expression that references the context item, context position, or context size results in a non-recoverable dynamic error.

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.

Sometimes the focus is based on a single node.

[Definition: A singleton focus based on a node N has the context item (and therefore the context node) set to N, and the context position and context size both set to 1 (one).]

2.5.2 Additional Context Variables

In addition to the values that make up the focus, an XSLT processor maintains a number of other internal variables that reflect aspects of the evaluation context. These variables are fully described in the sections of the specification that maintain and use these variables. They are:

The following non-normative table summarizes the initial state of each of the variables in the evaluation context, and the instructions which cause the state of the variable to change.

Variable Initial Setting Set by Cleared by
focus singleton focus based on the initial context node if supplied xsl:apply-templates, xsl:for-each, xsl:for-each-group, xsl:analyze-string calls on stylesheet functions
current template the initial template xsl:apply-templates, xsl:apply-imports, xsl:next-match xsl:for-each, xsl:for-each-group, calls on stylesheet functions
current mode the initial mode xsl:apply-templates calls on stylesheet functions
current group empty sequence xsl:for-each-group calls on stylesheet functions
current grouping key empty sequence xsl:for-each-group calls on stylesheet functions
current captured substrings empty sequence xsl:matching-substring xsl:non-matching-substring; calls on stylesheet functions
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

2.6 Parsing and Serialization

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

The stylesheet does not describe how a source tree is constructed. 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 the 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 [DOM2]). 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 XPath 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 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 20 Serialization) which 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, but is not required to do so.

2.7 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 18.1 Extension Functions.

It is also permissible to extend the language by providing new XSLT instructions. These are referred to as extension instructions, and are described in 18.2 Extension Instructions. A stylesheet that uses extension instructions 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 18 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 3.6.1 User-defined Data Elements).

2.8 Stylesheets and 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 SequenceType XP syntax defined in [XPath 2.0].

[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 a stylesheet.]

The conformance rules for XSLT 2.0, defined in 21 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 work unchanged with a schema-aware XSLT processor, unless the type information created as a result of schema processing introduces type errors (for example, an attribute of type xs:integer cannot be used as an argument of the concat FO function), or unless the type information changes the outcome of operations such as comparison and sorting.

There is a standard set of type definitions that are always available as in-scope schema components in every stylesheet. These are defined in 3.12 Built-in Types. The set of built-in types varies between a basic XSLT processor and a schema-aware XSLT processor.

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.

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.

Further, 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 the 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:template match="document-node(element(my:invoice))" priority="2">
. . .
</xsl:template>

<xsl:template match="document-node()" priority="1">
  <xsl:message terminate="yes">Source document is not an invoice</xsl:message>
</xsl:template>

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

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 the data model, as defined in [Data Model]. The implementation may choose one of several strategies for dealing with this situation:

  1. The processor may signal a non-recoverable 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 model 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 input data model 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 xdt:untypedAny and xdt: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 2.9 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 result tree. Validation is either strict or lax, as described in [XML Schema]. 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 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 19.2 Validation.

2.9 Error Handling

[Definition: An error that is 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 result tree.

There is an exception to this rule when the stylesheet specifies forwards-compatible behavior (see 3.9 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.]

[Definition: Some dynamic errors are classed as recoverable errors. When a recoverable error occurs, this specification allows the processor either to signal the error (by reporting the error condition and terminating execution) or to take a defined recovery action and continue processing.] It is implementation-defined whether the error is signaled or the recovery action is taken.

[Definition: If an implementation chooses to recover from a recoverable dynamic error, it must take the optional recovery action defined for that error condition in this specification.]

When the implementation makes the choice between signaling a dynamic error or recovering, it is not restricted in how it makes the choice; for example, it may provide options that can be set by the user. When an implementation chooses to recover from a dynamic error, it may also take other action, such as logging a warning message.

[Definition: A dynamic error that is not recoverable is referred to as a non-recoverable dynamic error. When a non-recoverable dynamic error occurs, 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 result tree 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 9.8 Circular Definitions.

The XPath specification states, in effect, that an XPath processor may evaluate a constant subexpression during the analysis phase, and if any error occurs during that evaluation, it may report this 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; instead, they must be held back until the evaluation phase, 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 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 non-recoverable 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

For example, the following construct contains a type error, because 42 is not allowed as an operand of the xsl:apply-templates instruction. 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:apply-templates select="42"/>
</xsl:if>

On the other hand, in the following example it is not possible to determine statically whether the operand of xsl:apply-templates 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:apply-templates 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 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 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.] As with other aspects of serialization, the handling of serialization errors is implementation-defined: see 20 Serialization.

The error codes used to label error conditions in this specification (and summarized in E Summary of Error Conditions) are provided for ease of reference. Implementations may use these codes when signaling errors, but they are not required to do so. An implementation that uses these codes within an API should treat the codes as unprefixed QNames; additional codes defined by an implementation (or by an application) can then use QNames in an implementation-defined namespace without risk of collision.

3 Stylesheet Structure

[Definition: A stylesheet consists of one or more stylesheet modules, each one forming all or part of a well-formed XML document.]

Note:

A stylesheet module, as defined here, contains XML in its raw textual form. In discussing the semantics of a stylesheet module, this specification frequently makes reference to nodes in the data model (see [Data Model]) that is generated when the XML document containing the stylesheet module is parsed. These references should not be taken as implying that an implementation must always start with stylesheet modules as textual XML documents, nor that it must represent the stylesheet internally as an instance of the data model.

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

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 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 3.11 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

3.1 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 3.6 Stylesheet Element and 3.7 Simplified Stylesheet Modules).

XSLT processors must use the XML namespaces mechanism [XML Namespaces 1.0] 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 18.2 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 however, are regarded as single words and are capitalized exactly as in XML Schema. This sometimes leads to composite function names such as current-dateTimeFO.

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/2003/11/xpath-functions is used for functions in the core function library, defined in [Functions and Operators]. ]

  • [Definition: The XML namespace, defined in [XML Namespaces 1.0] as http://www.w3.org/XML/1998/namespace, is used for attributes such as xml:lang and xml:space].

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

  • [Definition: The XPath datatypes namespace http://www.w3.org/2003/11/xpath-datatypes is used as defined in [Functions and Operators]]. In a stylesheet this namespace may be used to refer to the types xdt:untypedAtomic, xdt:yearMonthDuration, xdt:dayTimeDuration, xdt:anyAtomicType, and to the constructor functions associated with the first three of these types.

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

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 instructions: 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 XT0080] 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 2.0]) 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 result trees produced by the transformation to be different from the result trees that a conformant XSLT 2.0 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.

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 control what happens to a result tree once the transformation is complete. They may thus be used to provide additional parameters to the serializer, or to override the serialization behavior specified in 20 Serialization.

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.

Example: An Extension Attribute for xsl:message

For example, 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 XT0090] 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 will be registered for XSLT stylesheet modules.

The proposed definition of the media type is at B The 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 version, exclude-result-prefixes, extension-element-prefixes, 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:version, xsl:exclude-result-prefixes, xsl:extension-element-prefixes, or xsl:xpath-default-namespace.

It is recommended that 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, and any descendant elements of the element they appear on, together with attributes of those descendant elements. 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:]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 containing element on which the attribute appears.

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.

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 description of the xsl:stylesheet and xsl:transform elements only. This reflects the fact that these attributes are often used on the xsl:stylesheet element, in which case they apply to the entire stylesheet module.

Note that the effect of these attributes does not extend to stylesheet modules referenced by xsl:include or xsl:import declarations.

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

[xsl:]version

see 3.8 Backwards-Compatible Processing and 3.9 Forwards-Compatible Processing

[xsl:]xpath-default-namespace

see 5.2 Unprefixed QNames in Expressions and Patterns

[xsl:]exclude-result-prefixes

see 11.1.3 Namespace Nodes for Literal Result Elements

[xsl:]extension-element-prefixes

see 18.2 Extension Instructions

3.6 Stylesheet Element

<xsl:stylesheet
  id? = id
  extension-element-prefixes? = tokens
  exclude-result-prefixes? = tokens
  version = number
  xpath-default-namespace? = uri
  default-validation? = "strict" | "lax" | "preserve" | "strip">
  <!-- Content: (xsl:import*, other-declarations) -->
</xsl:stylesheet>

<xsl:transform
  id? = id
  extension-element-prefixes? = tokens
  exclude-result-prefixes? = tokens
  version = number
  xpath-default-namespace? = uri
  default-validation? = "strict" | "lax" | "preserve" | "strip">
  <!-- Content: (xsl:import*, 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.

[ERR XT0100] An xsl:stylesheet element must have a version attribute, indicating the version of XSLT that the stylesheet module requires.

[ERR XT0110] The value of the version attribute must be a number (specifically, it must be a DecimalLiteral XP as defined in [XPath 2.0].) For this version of XSLT, the value should normally be 2.0. A value of 1.0 indicates that the stylesheet module was written with the intention that it should be processed using an XSLT 1.0 processor.

If a stylesheet that specifies [xsl:]version="1.0" in the outermost element of the principal stylesheet module (that is, version="1.0" in the case of a standard stylesheet module, or xsl:version="1.0" in the case of a simplified stylesheet module) is submitted to an XSLT 2.0 processor, the processor should output a warning advising the user of possible incompatibilities, unless the user has requested otherwise. The processor must then process the stylesheet using the rules for backwards-compatible behavior. These rules require that if the processor does not support backwards-compatible behavior, it must signal an error and must not execute the transformation.

When the value of the version attribute is greater than 2.0, forwards-compatible behavior is enabled (see 3.9 Forwards-Compatible Processing).

Note:

XSLT 1.0 allowed the [xsl:]version attribute to take any numeric value, and specified that if the value was not equal to 1.0, the stylesheet would be executed in forwards compatible mode. XSLT 2.0 continues to allow the attribute to take any unsigned decimal value. A software product that includes both an XSLT 1.0 processor and an XSLT 2.0 processor (or that can execute as either) may use the [xsl:]version attribute to decide which processor to invoke; such behavior is outside the scope of this specification. When the stylesheet is executed with an XSLT 2.0 processor, the value 1.0 is taken to indicate that the stylesheet module was written with XSLT 1.0 in mind: if this value appears on the outermost element of the principal stylesheet module then an XSLT 2.0 processor will either reject the stylesheet or execute it in backwards compatible mode, as described above. Setting version="2.0" indicates that the stylesheet is to be executed with neither backwards nor forwards compatible behavior enabled. Any other value less than 2.0 enables backwards compatible behavior, while any value greater than 2.0 enables forwards compatible behavior.

When developing a stylesheet that is designed to execute under either XSLT 1.0 or XSLT 2.0, the recommended practice is to create two separate entry modules, one specifying version="1.0", and the other specifying version="2.0"; these entry modules can use xsl:include or xsl:import to incorporate the common code. Subsidiary stylesheet modules should specify version="2.0" if they make use of XSLT 2.0 facilities, and version="1.0" otherwise.

The default-validation attribute defines the default value of the validation attribute of all xsl:element, xsl:attribute, xsl:copy, xsl:copy-of, and xsl:result-document instructions, and of the xsl:validation attribute of all literal result elements. It also determines the validation applied to the implicit result tree created in the absence of an xsl:result-document instruction. This default applies within the stylesheet module: it does not extend to included or imported stylesheet modules. If the attribute is omitted, the default is strip. For details of the effect of this attribute, see 19.2 Validation.

[ERR XT0120] 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 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 3.6.1 User-defined Data Elements)]

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

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

If there are xsl:import elements, these must come before any other elements. Apart from this, the child elements of the xsl:stylesheet element may appear in any order. The ordering of these elements does not affect the results of the transformation unless there are conflicting declarations (for example, two template rules with the same priority that match the same node). In general, it is an error for a stylesheet to contain such conflicting declarations, but in some cases the processor is allowed to recover from the error by choosing the declaration that appears last in the stylesheet.

3.6.1 User-defined Data Elements

[Definition: In addition to declarations, the xsl:stylesheet element may contain 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 XT0130] 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,

[ERR XT0140] A user-defined data element must not precede an xsl:import element within a stylesheet module.

3.7 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="2.0"
      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="2.0"
                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="2.0"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

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

</xsl:stylesheet>

[ERR XT0150] 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 2.0; the value must be a DecimalLiteral XP as defined in [XPath 2.0].

Other literal result elements may also have an xsl:version attribute. When the xsl:version attribute is numerically less than 2.0, backwards-compatible processing behavior is enabled (see 3.8 Backwards-Compatible Processing). When the xsl:version attribute is numerically greater than 2.0, forwards-compatible behavior is enabled (see 3.9 Forwards-Compatible Processing).

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.

3.8 Backwards-Compatible Processing

[Definition: An element enables backwards-compatible behavior for itself, its attributes, its descendants and their attributes if it has an [xsl:]version attribute (see 3.5 Standard Attributes) whose value is less than 2.0.]

An element that has an [xsl:]version attribute whose value is greater than or equal to 2.0 disables backwards-compatible behavior for itself, its attributes, its descendants and their attributes. The compatibility behavior established by an element overrides any compatibility behavior established by an ancestor element.

If an attribute containing an XPath expression is processed with backwards-compatible behavior, then the expression is evaluated with XPath 1.0 compatibility mode set to true. For details of this mode, see Section XP.

Certain XSLT constructs also produce different results when backwards-compatible behavior is enabled. This is described separately for each such construct.

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.

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 2.0 processor are identical to the effects of processing the same stylesheet using an XSLT 1.0 processor. The differences are described (non-normatively) in K.1 Incompatible Changes. 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 2.0 processor are defined by the XPath 2.0 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 2.0 and XPath 2.0 specifications, it is not defined by reference to the XSLT 1.0 and XPath 1.0 specifications.

It is implementation-defined whether a particular XSLT 2.0 implementation supports backwards-compatible behavior.

[ERR XT0160] If an implementation does not support backwards-compatible behavior, then it is a non-recoverable dynamic error if any element is evaluated that enables backwards-compatible behavior.

Note:

To write a stylesheet that works with both XSLT 1.0 and 2.0 processors, while making selective use of XSLT 2.0 facilities, it is necessary to understand both the rules for backwards-compatible behavior in XSLT 2.0, and the rules for forwards-compatible behavior in XSLT 1.0. If the xsl:stylesheet element specifies version="2.0", then an XSLT 1.0 processor will ignore XSLT 2.0 declarations that were not defined in XSLT 1.0, for example xsl:function and xsl:import-schema. If any new XSLT 2.0 instructions are used (for example xsl:analyze-string or xsl:namespace), or if new XPath 2.0 features are used (for example, new functions, or syntax such as conditional expressions, or calls to a function defined using xsl:function), then the stylesheet must provide fallback behavior that relies on XSLT 1.0 and XPath 1.0 facilities only. 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.

3.9 Forwards-Compatible Processing

[Definition: An element enables forwards-compatible behavior for itself, its attributes, its descendants and their attributes if it has an [xsl:]version attribute (see 3.5 Standard Attributes) whose value is greater than 2.0.]

An element that has an [xsl:]version attribute whose value is less than or equal to 2.0 disables forwards-compatible behavior for itself, its attributes, its descendants and their attributes. The compatibility behavior established by an element overrides any compatibility behavior established by an ancestor element.

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.

Within a section of a stylesheet where forwards-compatible behavior is enabled, errors that would normally be static errors are treated instead as dynamic errors. This means that no error is signaled unless the construct containing the error is actually evaluated.

This includes, but is not limited to, the following situations:

  • if an element in the XSLT namespace appears as a child of the xsl:stylesheet element, and XSLT 2.0 does not allow such elements as declarations, then the element must be ignored along with its content;

  • if an element in the XSLT namespace appears in a sequence constructor and XSLT 2.0 does not allow such elements to occur in sequence constructors, then the processor must not signal an error, and if the element is evaluated, the processor must perform fallback for the element as specified in 18.2.3 Fallback;

  • if an element has an attribute that XSLT 2.0 does not allow the element to have, then the attribute must be ignored.

  • if an element has an optional attribute with a value that XSLT 2.0 does not allow the attribute to have, then the attribute must be ignored.

  • if an instruction element has a mandatory attribute with a value that XSLT 2.0 does not allow the attribute to have, then the error must not be signaled unless the instruction is actually evaluated.

  • if an attribute contains an XPath expression that does not match the allowed syntax of an XPath 2.0 expression, the error must not be signaled unless the expression is actually evaluated.

  • if an attribute contains an XPath expression that calls a function that cannot be identified by its name and arity, the error must not be signaled unless the function call is actually evaluated.

Example: Forwards Compatible Behavior

For example, an XSLT 2.0 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:choose>
      <xsl:when test="system-property('xsl:version') >= 17.0">
        <xsl:exciting-new-17.0-feature/>
      </xsl:when>
      <xsl:otherwise>
        <html>
        <head>
          <title>XSLT 17.0 required</title>
        </head>
        <body>
          <p>Sorry, this stylesheet requires XSLT 17.0.</p>
        </body>
        </html>
      </xsl:otherwise>
    </xsl:choose>
  </xsl:template>
</xsl:stylesheet>

Note:

If a stylesheet depends crucially on a declaration introduced by a version of XSLT after 2.0, then the stylesheet can use an xsl:message element with terminate="yes" (see 17 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')) < 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>

3.10 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.

3.10.1 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, it is resolved using the algorithm defined in [RFC2396], relative to the base URI of the xsl:include or xsl:import element as defined in [Data Model].

After resolving against the base URI, the way in which the URI reference is used to locate a stylesheet module is 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 3.7 Simplified Stylesheet Modules.

Implementations may choose to accept URI references containg a fragment identifier defined by reference to the XPointer specification (see [XPointer]). 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 XT0165] 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 conforming to this specification.

3.10.2 Stylesheet Inclusion

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

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 3.10.1 Locating Stylesheet Modules.

[ERR XT0170] 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 XT0180] 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'.

3.10.3 Stylesheet Import

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

A stylesheet module may import another stylesheet module using an xsl:import declaration. Importing a stylesheet module is the same as including it (see 3.10.2 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 3.10.1 Locating Stylesheet Modules.

[ERR XT0190] An xsl:import element must be a top-level element.

[ERR XT0200] The xsl:import element children must precede all other element children of an xsl:stylesheet element, including any xsl:include element children and any user-defined data elements.

Example: Using xsl:import

For example,

<xsl:stylesheet version="2.0"
                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:

         A
         |
     +---+---+
     |       |
     B       C
     |       |
     D       E

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 XT0210] 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.

3.11 Embedded Stylesheet Modules

A standalone stylesheet module is a complete XML document with the xsl:stylesheet element as its document element. However, a stylesheet module may also be embedded in another resource. Two forms of embedding are possible:

  • the XSLT stylesheet may be textually embedded in a non-XML resource, or

  • the xsl:stylesheet element may occur in an XML document other than as the document element.

To facilitate the second form of embedding, the xsl:stylesheet element may have an ID attribute that specifies a unique identifier.

Note:

In order for such an attribute to be used with the XPath id FO function, it must actually be declared in the DTD or schema as being of type ID. The same requirement typically applies if the identifier is to be used as a fragment identifier in a URI reference.

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 relative URI with 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="2.0"
                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 usage is subject to confirmation: see 3.4 XSLT Media Type. In the absence of a registered media type for XSLT stylesheets, some vendors' products have adopted different conventions, notably type="text/xsl".

Note:

Support for the xml-stylesheet processing instruction is not required for conformance with this Recommendation.

3.12 Built-in Types

Every XSLT 2.0 processor includes the following named type definitions in the in-scope schema components:

xs:string
xs:boolean
xs:integer
xs:decimal
xs:double
xs:date
xs:time
xs:dateTime
xs:QName
xs:anyURI
xdt:yearMonthDuration
xdt:dayTimeDuration
xdt:anyAtomicType
xdt:untypedAtomic

These types are defined in [XML Schema] (Part 2) in the case of the names prefixed xs:, and in [XPath 2.0] in the case of those prefixed xdt:.

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 Schemas or the Schema for Datatypes. The Schema for Datatypes, as well as defining built-in types such as xs:integer and xs:double, also defines types that are intended for use only within the Schema for DataTypes, such as xs:derivationControl. A stylesheet that is designed to process XML Schema documents as its input or output may import the Schema for Schemas.

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 18.1 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.

3.13 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 21 Conformance.

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

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 3.12 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 stylesheet, 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; importing components in one stylesheet module makes them available throughout the stylesheet.

The namespace and schema-location attributes are both optional.

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 present, 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.

  • 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 XT0220] 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 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.

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.

4 Data Model

The data model used by XSLT is the XPath 2.0 and XQuery 1.0 data model, 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 the data model as it is used by XSLT:

The rules in 4.2 Stripping Whitespace from the Stylesheet and 4.3 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 tree defined by the data model 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 data model defined in [Data Model] is capable of representing either an XML 1.0 document (conforming to [XML 1.0] and [XML Namespaces 1.0]) or an XML 1.1 document (conforming to [XML 1.1] and [XML Namespaces 1.1]), and it makes no distinction between the two. In principle, therefore, XSLT 2.0 can be used with either of these XML versions; the only differences arise outside the boundary of the transformation proper, either while creating the data model from textual XML (parsing), or while producing textual XML from the data model (serialization).

Construction of the data model is outside the scope of this specification, so XSLT 2.0 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 20 Serialization), though from a conformance point of view it is an optional feature. Although facilities are described for serializing the data model 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 data model 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 2.0 and XPath 2.0, for example the productions Char XML and NCName Names, 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. It is recommended that an XSLT 2.0 processor should implement the 1.1 versions.

At the time of writing there is no published version of [XML Schema] that references the XML 1.1 specifications. This means that data types such as xs:NCName and xs:ID are constrained by the XML 1.0 rules. It is recommended that an XSLT 2.0 processor should implement the rules in later versions of [XML Schema] 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:analyze-string
    xsl:apply-imports
    xsl:apply-templates
    xsl:attribute-set
    xsl:call-template
    xsl:character-map
    xsl:choose
    xsl:next-match
    xsl:stylesheet
    xsl:transform

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

[ERR XT0260] 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.

4.3 Stripping Whitespace from a Source Tree

A source document 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.

The stripping process takes as input a set of element names whose child whitespace text nodes are to be preserved.

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.

Note:

This implies that if an xml:space attribute is specified on a literal result element, it will be included in the result.

Note:

Where multiple transformations are to be applied to the same source document, a useful optimization is to do the whitespace stripping only once. Implementations may therefore allow whitespace stripping to be controlled as a separate operation from the rest of the transformation process.

<!-- 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 NameTests XP; an element name matches an xsl:strip-space or xsl:preserve-space element if it matches one of the NameTests XP. An element matches a NameTest XP if and only if the NameTest XP would be true for the element as an XPath node test. When more than one xsl:strip-space and xsl:preserve-space element matches, the best matching element is determined by the best matching NameTest XP. This is determined in the same way as with template rules:

[ERR XT0270] It is a recoverable dynamic error if this leaves more than one match. The optional recovery action is to select, from the matches that are left, the one that occurs last in declaration order.

Note:

A source document is supplied as input to the XSLT processor in the form of a tree conforming to the data model described in [Data Model]. Nothing in this specification states that this tree must be built by parsing an XML document; nor does it state that the application that constructs the tree is required to treat whitespace in any particular way. The provisions in this section relate only to whitespace text nodes that are present in the tree supplied as input to the processor. In particular, the processor cannot preserve whitespace text nodes unless they were actually present in the supplied tree.

4.4 Attributes Types and DTD Validation

The data model allows attribute nodes to have type annotations derived from schema processing. It is also possible for a limited set of type annotations (on attributes only) to be derived from DTD-based validation of a source document. Because the construction of the data model is outside the scope of XSLT processing, this specification (in common with [Data Model]) neither requires nor prevents this. This section merely points out some of the consequences of the decision.

In general, creating type annotations based on DTD attribute types is likely to create some backwards compatibility problems. For example, an attribute annotated with type xs:NMTOKENS will have a different typed value than if it were annotated as xdt:untypedAtomic. If the value of the colors attribute is red green blue, then the expression @colors = "red" will return true if the type annotation is xs:NMTOKENS, but false if the type annotation is xdt:untypedAtomic.

Special considerations apply to ID attributes, because in XSLT 1.0, attributes defined in a DTD as having type ID were explicitly recognized by the XPath id FO function. An XSLT 2.0 processor wishing to offer the best possible backwards compatibility should therefore recognize ID attributes during DTD processing, and annotate the resulting nodes accordingly, even though it does not recognize other DTD-based types such as NMTOKENS.

The conformance rules for a basic XSLT processor do not allow attribute nodes to be annotated with type xs:ID. For backwards compatibility reasons, however, a processor may implement the id FO function so that it recognizes attributes defined in a DTD as being ID attributes, even though they are not annotated as being of type xs:ID in the data model.

A basic XSLT processor does not allow nodes to be annotated as being of type xs:IDREF or xs:IDREFS, which means that with such a processor, the idref FO function will always return an empty sequence.

4.5 Disable Output Escaping

For backwards compatibility reasons, XSLT 2.0 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 20.1 Character Maps) is 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, xsl:value-of, and xsl:attribute (see 20.2 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 or attribute node.

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 Syntactic Constructs

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 specified as a QName using the syntax for QNameNames as defined in [XML Namespaces 1.0].

[Definition: A QName is always written in the form (NCName ":")? NCName, that is, a local name optionally preceded by a namespace prefix. When two QNames are compared, however, they are considered equal if the corresponding expanded-QNames are the same, as described below.]

Because an atomic value of type xs:QName is sometimes referred to loosely as a QName, this specification also uses the term lexical QName to emphasize that it is referring to a QNameNames in its lexical form rather than its expanded form. This term is used especially when strings containing lexical QNames are manipulated as run-time values.

[Definition: A lexical QName is a string representing a QName in the form (NCName ":")? NCName, that is, a local name optionally preceded by a namespace prefix.]

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

[Definition: An expanded-QName is a pair of values containing a local name and an optional namespace URI. Two expanded-QNames are equal if the namespace URIs are the same (or both absent) and the local names are the same.]

If the 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 (as defined by a namespace declaration of the form xmlns="some.uri") is not used for unprefixed names.

There are two cases where the default namespace from the static context is used when expanding an unprefixed QName:

  1. Where a QName is used to define the name of an element being constructed in the result tree. 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.

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 QNames in Expressions and Patterns.

[ERR XT0280] In the case of a prefixed QName used as 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 QName.

[ERR XT0290] Where the result of evaluating an XPath expression (or an attribute value template) is required to be a lexical QName, then unless otherwise specified it is a non-recoverable dynamic error if the defining element has no namespace node whose name matches the prefix of the lexical QName. This error may be signaled as a static error if the value of the expression can be determined statically.

Note:

In some cases this is defined as a recoverable dynamic error, for example when evaluating the name attribute of xsl:element and xsl:attribute

5.2 Unprefixed 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 of that element. The effect of this is specified in [XPath 2.0]; 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:

  • any unprefixed element name or type name used in a pattern

  • any unprefixed element name used in the elements attribute of the xsl:strip-space or xsl:preserve-space instructions

  • any unprefixed element name or type name used in the as attribute of an XSLT instructions

  • any unprefixed type name used in the type attribute of an XSLT instruction.

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 (as defined by an xmlns="some-uri" declaration) is not used.

The attribute does not affect other names, for example function names, variable names, or names used as arguments to the key or system-property functions.

5.3 Expressions

XSLT uses the expression language defined by XPath 2.0 [XPath 2.0]. 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 the result tree.

[Definition: Within this specification, the term XPath expression, or simply expression, means a string that matches the production ExprXP defined in [XPath 2.0].]

An XPath expression may occur as the value of certain attributes on XSLT-defined elements, and also within curly brackets in attribute value templates.

[ERR XT0300] Except where forwards-compatible behavior is enabled (see 3.9 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, does not match the XPath production ExprXP, 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.

[ERR XT0310] The transformation fails with a non-recoverable dynamic error if any XPath expression is evaluated and raises a dynamic error.

[ERR XT0320] 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.

[Definition: The context within a stylesheet where an XPath expression appears may specify the required type of the expression. The required type indicates the data type of 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 2.0] 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 2.0 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.

XPath defines the concept of an expression contextXP which contains all the information that can affect the result of evaluating an expression. The evaluation context has two parts, the static contextXP, and the dynamic contextXP. The components that make up the expression context are defined in the XPath specification (see Section 2.1 Expression ContextXP). The following paragraphs describe the way in which these components are initialized when an XPath expression is contained within an XSLT stylesheet.

5.3.1 Initializing the Static Context

The static contextXP 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 whose value contains the XPath expression in question.

5.3.2 Initializing the Dynamic Context

The dynamic contextXP of an XPath expression appearing in an XSLT stylesheet is initialized as follows.

  • Where the containing element 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.

    In other cases, the rules are given in the specification of the containing element.

  • The dynamic variablesXP 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 timezoneXP is implementation-defined.

  • The available documentsXP, and the available collectionsXP are implementation-dependent.

    The available documentsXP are defined as part of the XPath 2.0 dynamic context to support the doc FO function, but this variable is also referenced by the similar XSLT document function: see 16.1 Multiple Source Documents. This variable defines a mapping between URIs passed to the doc FO or document function and the document nodes that are returned.

    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.

    Unlike the doc FO function, 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. Therefore, the information supplied in available documentsXP 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.

5.4 Patterns

A template rule identifies the nodes 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 16.3 Keys).

[Definition: A pattern specifies a set of conditions on a node. A node that satisfies the conditions matches the pattern; a node that does not satisfy the conditions does not match the pattern. The syntax for patterns is a subset of the syntax for expressions.] As explained in detail below, a node matches a pattern if the node can be selected by deriving an equivalent expression, and evaluating this expression with respect to some possible context.

Example: Patterns

Here are some examples of patterns:

  • para matches any para element.

  • * matches any 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.

  • 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(element(my:invoice)) matches the document node of a document whose document element matches the element declaration my:invoice.

  • text() matches any text node.

  • node() matches any node other than an attribute node, namespace node, or document node.

  • id("W33") matches the element with unique ID.

  • 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.

[ERR XT0340] Where an attribute is defined to contain a pattern, it is a static error if the pattern does not match the production Pattern. Every pattern is a legal XPath expression, but the converse is not true: 2+2 is an example of a legal XPath expression that is not a pattern. The XPath expressions that can be used as patterns are those that match the grammar for Pattern, given below.

Informally, a Pattern is a set of path expressions separated by | or union, where each step in the path expression is constrained to be an AxisStep XP that uses only the child or attribute axes. Patterns may also use the // operator. Predicates XP in a pattern can contain arbitrary XPath expressions (enclosed between square brackets) in the same way as predicates in a path expression.

Patterns may start with an id FO or key function call, provided that the value to be matched is supplied as either a literal or a reference to a variable or parameter, and the key name (in the case of the key function) is supplied as a string literal. These patterns will never match a node in a tree whose root is not a document node.

If a pattern occurs in part of the stylesheet where backwards compatible behavior is enabled (see 3.8 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.

Patterns
[1]    Pattern    ::=    PathPattern
| Pattern ('|' | 'union') PathPattern
[2]    PathPattern    ::=    RelativePathPattern
| '/' RelativePathPattern?
| '//' RelativePathPattern
| IdKeyPattern (('/' | '//') RelativePathPattern)?
[3]    RelativePathPattern    ::=    PatternStep (('/' | '//') RelativePathPattern)?
[4]    PatternStep    ::=    PatternAxis? NodeTest XP Predicates XP
[5]    PatternAxis    ::=    ('child' '::' | 'attribute' '::' | '@')
[6]    IdKeyPattern    ::=    'id' '(' IdValue ')'
| 'key' '(' StringLiteral XP ',' KeyValue ')'
[7]    IdValue    ::=    StringLiteral XP | VarRef XP
[8]    KeyValue    ::=    Literal XP | VarRef XP

The constructs NodeTest XP, Predicates XP, VarRef XP, Literal XP, and StringLiteral XP are part of the XPath expression language, and are defined in [XPath 2.0].

The meaning of a pattern is defined formally as follows.

First we define the concept of an equivalent expression. In general, the equivalent expression is the XPath expression that takes the same lexical form as the pattern as written. However, if the pattern contains a PathPattern that is a RelativePathPattern, then the first PatternStep PS of this RelativePathPattern is adjusted to allow it to match a parentless element or attribute node, as follows:

  • 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.

  • 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.

  • If PS uses the attribute axis, 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.

The axes child-or-top and attribute-or-top are introduced only for definitional purposes. They cannot be used explicitly in a user-written pattern or expression.

Note:

The purpose of these adjustments 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.

Let the equivalent expression, calculated according to these rules, be EE.

To determine whether a node N matches the pattern, evaluate the expression root(.)//(EE) with a singleton focus based on N. If the result is a sequence of nodes that includes N, then node N matches the pattern; otherwise node N does not match the pattern.

Example: The Semantics of Patterns

For example, 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 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.

Although the semantics of patterns are specified formally in terms of expression evaluation, it is possible to understand pattern matching using a different model. In a pattern, | indicates alternatives; a pattern with one or more | separated alternatives matches if any one of the alternatives matches. A 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.

The way in which the processor evaluates a pattern may affect the detection of dynamic errors. For example, given the pattern chapter[P]/section[Q], where P and Q are arbitrary expressions, an error in evaluating Q might or might not be signaled while matching a section element that has no chapter parent, and an error in evaluating P might or might not be signaled while matching an element that is not a section. In general, it is well defined whether a node matches a pattern, but it is not well defined whether or not dynamic errors will be signaled when evaluating a pattern against a node that does not match the pattern.

One particular optimization is required by this specification: for a PathPattern that starts with / or // or with an IdKeyPattern, the result of testing this pattern against a node in a tree whose root is not a document node must be a non-match, rather than a dynamic error. This rule applies to each to each PathPattern within a Pattern.

Note:

Without the above rule, any attempt to apply templates to a parentless element node would create the risk of a dynamic error if the stylesheet has a template rule specifying match="/".

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.

5.5 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 ({})].

An attribute value template consists 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 StringLiteral XP or within a comment.

[ERR XT0350] It is a static error if an unescaped left curly bracket appears in a fixed part of an attribute value template without a matching right curly bracket.

[ERR XT0360] It is a static error if the string contained between matching curly brackets in an attribute value template does not match the XPath production ExprXP.

[ERR XT0370] It is a static error if an unescaped right curly bracket occurs in a fixed part of an attribute value template.

[Definition: The result of evaluating an attribute value template is referred to as the effective value of the attribute.] 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 by atomizing the result of the expression using the procedure defined in [XPath 2.0], and then converting each of the atomic values in the atomized sequence to a string, adding a single space after each value other than the last. If the atomized sequence is empty, the result is a zero-length string.

Note:

This process can generate dynamic errors, for example if the sequence contains an xs:QName (which cannot be cast to a string), or an element with a complex content type (which cannot be atomized).

If backwards compatible behavior is enabled for the attribute, the rules for converting the value of the expression to a string 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.

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 not designated as attribute value templates. Namespace declarations are not attribute nodes in the data model and are therefore never treated as attribute value templates.

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 cannot be Nested

For example:

<a href="#{id({@ref})/title}">

is not allowed. Instead, use simply:

<a href="#{id(@ref)/title}">

5.6 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 and atomic values. The way that the resulting sequence is used depends on the containing instruction.]

Many XSLT elements (including literal result elements) are defined to take a sequence constructor as their content.

Four kinds of nodes may be encountered in a sequence constructor:

  • Text nodes appearing in the stylesheet (if they have not been removed in the process of whitespace stripping: see 4.2 Stripping Whitespace from the Stylesheet) are copied to create a new parentless text node in the result sequence.

  • Literal result elements are evaluated to create a new parentless element node, having the same expanded-QName as the literal result element, which is added to the result sequence: see 11.1 Literal Result Elements

  • XSLT instructions produce a sequence of zero, one, or more items as their result. These items are added to the result sequence. For most XSLT instructions, these items are nodes, but some instructions (xsl:sequence and xsl:copy-of) can also produce atomic values. 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, or existing nodes.

  • Extension instructions (see 18.2 Extension Instructions) also produce a sequence of items as their result. The items in this sequence are added to the result sequence.

There are several ways the result of a sequence constructor may be used.

  • The sequence may be bound to a variable or returned from a stylesheet function, in which case it becomes available as a value to be manipulated in arbitrary ways by XPath expressions. The sequence is bound to a variable when the sequence constructor appears within one of the elements xsl:variable, xsl:param, or xsl:with-param, when this instruction has an as attribute. The sequence is returned from a stylesheet function when the sequence constructor appears within the xsl:function element.

    Note:

    This will typically expose to the stylesheet elements, attributes, and other nodes that have not yet been attached to a parent node in a result tree. The semantics of XPath expressions when applied to parentless nodes are well-defined; however, such expressions should be used with care. For example, the expression / selects the root node of the tree containing the context node, which will not necessarily be a document node. The expression /E selects an E element child of the root node of the tree: if the root node is itself an E element, this expression will not select it.

    Parentless attribute nodes require particular care because they have no namespace nodes associated with them. This means, for example, that the name FO function will not be able to determine a prefix to use when reporting the name of the attribute. When a parentless attribute node has content containing namespace prefixes (for example, a QName or an XPath expression) then there is no information allowing the prefix to be resolved to a namespace URI. Parentless attributes can be useful in an application (for example, they provide an alternative to the use of attribute sets: see 10.2 Named Attribute Sets) but they need to be handled with care.

  • The sequence may be returned as the result of the containing element. This happens when the instruction containing the sequence constructor is xsl:analyze-string, xsl:apply-imports, xsl:apply-templates, xsl:call-template, xsl:choose, xsl:fallback, xsl:for-each, xsl:for-each-group, xsl:if, xsl:matching-substring, xsl:next-match, xsl:non-matching-substring, xsl:otherwise, xsl:perform-sort, xsl:sequence, or xsl:when

  • The sequence may be used to construct the content of a new element or document node. This happens when the sequence constructor appears as the content of a literal result element, or of one of the instructions xsl:copy, xsl:element, or xsl:message. It also happens when the sequence constructor is contained in one of the elements xsl:variable, xsl:param, or xsl:with-param, when this instruction has no as attribute. For details, see 5.6.1 Constructing Complex Content.

  • The sequence may be used to construct the string value of an attribute node, text node, namespace node, comment node, or processing instruction node. This happens when the sequence constructor is contained in one of the elements xsl:attribute, xsl:value-of, xsl:namespace, xsl:comment, or xsl:processing-instruction. For details, see 5.6.2 Constructing Simple Content.

Note:

The term sequence constructor replaces template as used in XSLT 1.0. The change is made partly for clarity (to avoid confusion with template rules and named templates), but also to reflect a more formal definition of the semantics. Whereas XSLT 1.0 described a template as a sequence of instructions that write to the result tree, XSLT 2.0 describes a sequence constructor as something that can be evaluated to return a sequence of items; what happens to these items depends on the containing instruction.

5.6.1 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:result-document, or a literal result element.

The sequence is processed as follows:

  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. Special considerations apply to two atomic types for which casting to xs:string is not possible:

  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 with a single space (#x20) used as a separator between successive strings. If this process would create a text node whose string value is zero-length, no text node is created and the content is discarded.

  4. Any document node within the result sequence is replaced by a sequence containing each of its children, in document order.

  5. Adjacent text nodes within the result sequence are merged into a single text node.

  6. Invalid namespace and attribute nodes are detected as follows.

    [ERR XT0410] It is a recoverable 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. The optional recovery action is to ignore the offending namespace or attribute node.

    [ERR XT0420] It is a recoverable dynamic error if the result sequence used to construct the content of a document node contains a namespace node or attribute node. The optional recovery action is to ignore the offending namespace or attribute node.

    [ERR XT0430] It is a recoverable 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). The optional recovery action is to discard all conflicting namespace nodes other than the one that appears last in the result sequence.

    [ERR XT0440] It is a recoverable 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). The optional recovery action is to ignore the offending namespace node.

  7. 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 undefined, it is not significant which of the duplicates is retained.

  8. 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.

  9. 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 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 [XMLBASE]) that overrides this.

  10. If the newly constructed node is an element node, then namespace fixup is applied to this node, as described in 5.6.3 Namespace Fixup

Example: A Sequence Constructor for Complex Content

For example, 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.

5.6.2 Constructing Simple Content

The xsl:attribute, xsl:comment, xsl:processing-instruction, xsl:namespace, and xsl:value-of elements 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 in the following way:

  1. The sequence is atomized.

  2. Every value in the atomized sequence is cast to a string. Special considerations apply to atomic values of type xs:QName:

    • [ERR XT0450] A recoverable dynamic error occurs if the sequence contains a value of type xs:QName, because such values cannot be cast to a string. The optional recovery action is to ignore the xs:QNamevalue.

      Note:

      An example showing how to construct QName-valued attributes (specifically, an xsi:type attribute) is given in 11.6 Creating Namespace Nodes. Essentially, the application is responsible for choosing a namespace prefix, and this can then be used firstly to create a namespace node by using the xsl:namespace instruction, and secondly to construct the lexical QName, which is then written directly as the attribute value.

  3. The strings within the resulting sequence are concatenated, with a (possibly zero-length) separator inserted between successive strings. When the select attribute is used the default separator is a single space character (#x20). When the value is constructed using a sequence constructor, the default separator is a zero-length string. 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 the default separator cannot be changed.

  4. The string that results from this concatenation forms the string value of the new attribute, namespace, comment, processing-instruction, or text node.

5.6.3 Namespace Fixup

In a tree supplied to or constructed by an XSLT processor, the following constraints relating to namespace nodes must be satisfied in addition to those specified in [Data Model]:

  • 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.

  • If an element is annotated with the type xs:QName, or a type derived from xs:QName, or if it has an attribute with such a type annotation, then that element must have a namespace node whose string value is the same as the namespace URI of that QName value, and whose name is the same as the prefix used in the lexical representation of the QName (if the lexical representation is unprefixed, the namespace node must be unnamed).

[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 above 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-defined, 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 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, documents loaded using the document, doc FO or collection FO function, documents supplied as the value of a stylesheet parameter, or documents returned by an extension function or extension instruction.

[ERR XT0490] It is a recoverable dynamic error if such a source document does not already satisfy the constraints listed above . This is a recoverable error. The optional recovery action is either to perform namespace fixup, or to produce implementation-dependent results.

In an InfoSet (see [XML Information Set]) created from a document conforming to [XML Namespaces 1.0], 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 [XML Namespaces 1.1]. XSLT 2.0 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.

Note:

This has implications on serialization, defined in [XSLT and XQuery Serialization]. It means that it is possible to create 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, xmlms:foo="") to prevent this inheritance taking place.

6 Template Rules

Template rules define the processing that can be applied to nodes that match a particular pattern.

6.1 Defining Templates

<!-- Category: declaration -->
<xsl:template
  match? = pattern
  name? = qname
  priority? = number
  mode? = tokens
  as? = sequence-type>
  <!-- Content: (xsl:param*, sequence-constructor) -->
</xsl:template>

[Definition: An xsl:template declaration defines a template, which contains a sequence constructor for creating nodes and/or atomic values. A template can serve either as a template rule, invoked by matching nodes 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.]

An xsl:template element must have either a match attribute or a name attribute, or both. If it has a match attribute, then it is a template rule. If it has a name attribute, then it is a named template. An xsl:template element that has no match attribute must have no mode attribute and no priority attribute.

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 5.6 Sequence Constructors). If an as attribute is present, the as attribute defines the required type of the result.

The result of evaluating the sequence constructor is 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.

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 node or nodes 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 node used as the context node.

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 a node 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 node, 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 nodes in the source tree, and produces as output a sequence of items; these will often be nodes to be added to the 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 node in the input sequence is processed by finding a template rule whose pattern matches that node. If there is more than one, 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 node, a built-in template rule is used (see 6.6 Built-in Template Rules). The chosen template rule is evaluated. The rule that matches the Nth node in the sorted sequence is evaluated with that node 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 node in the sorted sequence) are then concatenated, to form a single sequence. They are concatenated retaining the order of the nodes 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 context node to be processed.

Note:

This includes child element nodes, text nodes, comments, and processing instructions. It does not, however, include attributes.

[ERR XT0510] It is a recoverable dynamic error if an xsl:apply-templates instruction with no select attribute is evaluated when the context item is not a node. The optional recovery action is to return the empty sequence.

Note:

If stripping of whitespace text nodes has not been enabled for an element, then all whitespace in the content of the element will be processed as text, and thus whitespace between child elements will count in determining the position of a child element as returned by the position FO function. This typically means that the child elements will be numbered 2, 4, 6... This effect can be prevented by stripping whitespace text nodes as specified in 4.3 Stripping Whitespace from a Source Tree, or by writing <xsl:apply-templates select="*"/> to avoid processing the child text nodes.

A select attribute can be used to process nodes selected by an expression instead of processing all children. The value of the select attribute is an expression. The expression must evaluate to a sequence of nodes (it can contain zero, one, or more nodes).

[ERR XT0520] It is a type error if the sequence returned by the select expression contains an item that is not a node.

Note:

In XSLT 1.0, the select attribute selected a set of nodes, which by default were processed in document order. In XSLT 2.0, it selects a sequence of nodes. In cases that would have been valid in XSLT 1.0, the expression will return a sequence of nodes in document order, so the effect is the same.

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 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 6.7 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"

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 node in a source document to match more than one template rule. When this happens, only one template rule is evaluated for the node. The template rule to be used is determined as follows:

  1. First, all matching template rules that have lower import precedence than the matching template rule or rules with the highest import precedence are eliminated from consideration.

  2. Next, all matching template rules that have lower priority than the matching template rule or rules with the highest priority are eliminated from consideration. The priority of a template rule is specified by the priority attribute on the template rule.

    [ERR XT0530] The value of this must be a decimal number (positive or negative), matching the production IntegerLiteral XP or DecimalLiteral XP with an optional leading minus sign (-).

    [Definition: If no priority attribute is specified on the 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:

    • If the pattern contains multiple alternatives separated by | or union, then the template rule is treated equivalently to a set of template rules, one for each alternative. However, it is not an error if a node matches more than one of the alternatives.

    • If the pattern has the form /, then the priority is −0.5.

    • If the pattern has the form of a QName optionally preceded by a PatternAxis or has the form processing-instruction(StringLiteral XP) or processing-instruction(NCName Names) optionally preceded by a PatternAxis, then the priority is 0.

    • If the pattern has the form of an ElementTest XP or AttributeTest XP, optionally preceded by a PatternAxis, 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. A SchemaContextPath XP may be specified in addition to the element or attribute name; this does not affect the priority. The presence or absence of the keyword nillable 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 (matches by substitution group)
      element(*,T) 0 (matches by type only)
      attribute(*,T) 0 (matches by type only)
      attribute(A,*) 0 (equivalent to @A)
      element(E,T) 0.25 (matches by substitution group and type)
      element(E) 0.25 (matches by substitution group and type)
      attribute(A,T) 0.25 (matches by name and type)
      attribute(A) 0.25 (matches by name and type)
    • If the pattern has the form of a DocumentTest XP, then if it includes no ElementTest XP the priority is −0.5. If if does include an ElementTest XP, then the priority is the same as the priority of that ElementTest XP, computed according to the table above.

    • If the pattern has the form NCName Names:* or *:NCName Names, optionally preceded by a PatternAxis, then the priority is −0.25.

    • If the pattern is any other NodeTest XP, optionally preceded by a PatternAxis, then the priority is −0.5.

    • Otherwise, 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.

[ERR XT0540] It is a recoverable dynamic error if the conflict resolution algorithm for template rules leaves more than one matching template rule. The optional recovery action is to select, from the matching template rules that are left, the one that occurs last in declaration order.

6.5 Modes

[Definition: Modes allow a node in the 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 16.1 Multiple Source Documents) or when processing temporary trees (see 9.4 Temporary Trees)]

Modes are identified by a QName, except for the default mode, which is unnamed.

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. If the attribute is present, then its value must be a space-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:

  • a QName, 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

  • the token #all, to indicate that the template rule is applicable to all modes.

[ERR XT0550] It is a static error if the same token is included more than once in the list 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 either be a QName, which is expanded as described in 5.1 Qualified Names to define the name of a mode, or the token #default, to indicate that the default mode is to be used, or the token #current, to indicate that the current mode is to be used. If the attribute is omitted, the default mode is used.

When searching for a template rule to process each node 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 default mode, unless a different initial mode has been supplied, 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 stylesheet function is called, the current mode becomes the default mode. No other instruction changes the current mode. 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 6.7 Overriding Template Rules).

6.6 Built-in Template Rules

When a node is selected by xsl:apply-templates and there is no template rule in the stylesheet that can be used to process that node, a built-in template rule is evaluated instead.

The built-in template rules apply to all modes.

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.

Example: Using a Built-In Template Rule

For example, suppose the stylesheet contains the following instruction:

<xsl:apply-templates select="title" mode="mm">
  <xsl:with-param name="init" select="10"/>
</xsl:apply-template>

If there is no explicit template rule that matches the title element, then the following implicit rule is used:

<xsl:template match="title" mode="#all">
  <xsl:with-param name="init"/>
  <xsl:apply-templates mode="#current">
    <xsl:with-param name="init" select="$init"/>
  </xsl:apply-templates>
</xsl:template>

The built-in template rule for text and attribute nodes returns a text node containing the string value of the context node, unless the string value is zero-length, in which case it returns an empty sequence. It is effectively:

<xsl:template match="text()|@*" mode="#all">
  <xsl:value-of select="."/>
</xsl:template>

The built-in template rule for processing instructions and comments does nothing (it returns the empty sequence).

<xsl:template match="processing-instruction()|comment()" mode="#all"/>

The built-in template rule for namespace nodes is also to do nothing. There is no pattern that can match a namespace node, so the built-in template rule is always used when xsl:apply-templates selects a namespace node.

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.

6.7 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. Both instructions will invoke the built-in template rule for the node (see 6.6 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 by matching a pattern, the template rule becomes the current template rule for the evaluation of the rule's sequence constructor. When an xsl:for-each or xsl:for-each-group instruction is evaluated, or when a stylesheet function is called (see 10.3 Stylesheet Functions), the current template rule becomes null 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 null.

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, and is always a node.

Both xsl:apply-imports and xsl:next-match search for a template rule that matches the context node, and that is applicable to the current mode (see 6.5 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. If the processor has recovered from the error that occurs when two matching template rules have the same import precedence and priority, then it also considers all matching template rules with the same import precedence and priority that occur before the current template rule in declaration order.

If no matching template rule is found that satisfies these criteria, the built-in template rule for the node kind is used (see 6.6 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 10.1.1 Passing Parameters to Templates). It also passes on any tunnel parameters as described in 10.1.2 Tunnel Parameters.

[ERR XT0560] It is a non-recoverable dynamic error if xsl:apply-imports or xsl:next-match is evaluated when the current template rule is null.

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 processor, but can be used to define fallback behavior when the stylesheet is processed by an XSLT 1.0 processor in forwards-compatible mode.

7 Repetition

<!-- Category: instruction -->
<xsl:for-each
  select = sequence-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, and the expression must evaluate to 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, which is evaluated once for each item in the sorted sequence. The sequence constructor is evaluated with the focus set as follows:

For each item in the input sequence, evaluating the sequence constructor produces a sequence of items (see 5.6 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.

Note:

With XSLT 1.0, the selected nodes were processed in document order. With XSLT 2.0, XPath expressions that would have been valid under XPath 1.0 (such as path expressions and union expressions) will return a sequence of nodes that is already in document order, so backwards compatibility is maintained.

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>

8 Conditional Processing

There are two instructions in XSLT that support conditional processing in a template: 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.

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 valueXP of the expression in the test attribute. The rules for determining the effective boolean value of an expression are given in [XPath 2.0]: 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 5.6 Sequence Constructors), and the resulting node 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 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 valueXP of the expression in its test attribute is true. The rules for determining the effective boolean value of an expression are given in [XPath 2.0]: 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>

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, or a function parameter. A parameter is a variable with the additional property that its value can be set by the caller when the stylesheet, the template, or the function is invoked.]

[Definition: A variable is a binding between a name and a value. The value of a variable is any sequence (of nodes and/or atomic values), as defined in [Data Model].]

9.1 Variables

<!-- Category: declaration -->
<!-- Category: instruction -->
<xsl:variable
  name = qname
  select? = expression
  as? = sequence-type>
  <!-- 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 a QName, 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 SequenceType XP, as defined in [XPath 2.0].

[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 XT0570] 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.

9.2 Parameters

<!-- Category: declaration -->
<xsl:param
  name = qname
  select? = expression
  as? = sequence-type
  required? = "yes" | "no"
  tunnel? = "yes" | "no">
  <!-- Content: sequence-constructor -->
</xsl:param>

The xsl:param element may be used as a child of xsl:stylesheet, to define a parameter to the transformation; or as a child of xsl:template to define a parameter to a template, which may be supplied when the template is invoked using xsl:call-template, xsl:apply-templates, xsl:apply-imports or xsl:next-match; or as a child of xsl:function to define a parameter to a stylesheet function, which may be supplied when the function is called from an XPath expression.

The xsl:param element has a required name attribute, which specifies the name of the parameter. The value of the name attribute is a QName, which is expanded as described in 5.1 Qualified Names.

[ERR XT0580] It is a static error if two parameters of a template or of a stylesheet function have the same name.

Note:

For rules concerning stylesheet parameters, see 9.5 Global Variables and Parameters. Local variables may shadow template parameters and function parameters: see 9.7 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 function, or whether the same foo element node will be used for each invocation. However, it is permissible for the default value to be 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 SequenceType XP, as defined in [XPath 2.0].

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 XT0590] 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. 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 XT0600] 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 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 XT0610] 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 non-recoverable dynamic error if the caller supplies no value for the parameter.

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 the variable or 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="''"/>
    
  • [Definition: 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 (referred to as a temporary tree) is constructed with a document node having as its children the sequence of nodes that results from evaluating the sequence constructor.] Temporary trees are described in more detail in 9.4 Temporary Trees.

  • 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 5.6 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 temporary tree
absent present present Value is obtained by evaluating the sequence constructor, adjusted to the type required by the as attribute

[ERR XT0620] 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 xdt: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 document node containing an empty element as a child (that is, a temporary tree):

<xsl:variable name="doc"><c/></xsl:variable>

The value of the following variable is 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 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()"/>

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 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 Temporary Trees

A temporary tree is constructed by evaluating an xsl:variable, xsl:param, or xsl:with-param element that has non-empty content and that has no as attribute. This element is referred to as the variable-binding element. The value of the variable is a single node, the document node of the temporary tree. This document node is created implicitly, and its content is formed from the result of evaluating the sequence constructor owned by the variable-binding element, as described in 5.6.1 Constructing Complex Content.

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 (see [Data Model]). Thus, the base URI of the document node will be equal to the base URI of the variable-binding element; 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.

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 id FO functions can be used to find nodes within a temporary tree, provided that at the time the function is called, the context item is a node within the temporary tree.

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 6.5 Modes):

<xsl:stylesheet
  version="2.0"
  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 nodes from different trees cannot 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 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.

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 XT0630] It is a static error if a stylesheet contains more than one 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 document node of the document containing the initial context node. 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 node is supplied.

Example: A Stylesheet Parameter

The following example declares a global parameter para-font-size, which it references 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 Local Variables and Parameters

[Definition: As well as being allowed as declaration elements, the xsl:variable element is also allowed in sequence constructors. Such a variable is known as a local variable.]

[Definition:  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. ]

[Definition:  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.]

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.

9.7 Scope of Variables

For any variable-binding element, there is a region 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. The binding is not visible for the xsl:variable or xsl:param element itself.

[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 or xsl:param element shadows another binding established by another local xsl:variable or xsl:param. However, such shadowing is discouraged and implementations may output a warning when it occurs.

Example: Local Variable Shadowing a Local Variable

The following is not an error, but is discouraged, because 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:template name="foo">
  <xsl:variable name="x" select="1"/>
  <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 2.0].

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.

9.8 Circular Definitions

[Definition: 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. If it is impossible to do this for all global variable definitions, then a circularity is said to exist.]

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 XT0640] In general, a circularity in a stylesheet is a non-recoverable 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 16.3 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 = qname>
  <!-- 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 a QName, 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 attribute on an xsl:template element has no effect when the template is invoked by an xsl:apply-templates instruction.

[ERR XT0650] 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 xsl:template in the stylesheet.

[ERR XT0660] It is a static error if a stylesheet contains more than one template with the same name and the same import precedence, unless it also contains a template with the same name and higher import precedence.

The target template for an xsl:call-template instruction is the template whose name attribute matches the name attribute of the xsl:call-template instruction and that has higher import precedence than any other template with this name. The result of evaluating an xsl:call-template instruction is the sequence produced by evaluating the sequence constructor contained in its target template (see 5.6 Sequence Constructors).

10.1.1 Passing Parameters to Templates

<xsl:with-param
  name = qname
  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 a QName, which is expanded as described in 5.1 Qualified Names.

xsl:with-param is allowed within xsl:call-template, xsl:apply-templates, xsl:apply-imports, and xsl:next-match.

[ERR XT0670] It is a static error if a single xsl:call-template, xsl:apply-templates, xsl:apply-imports, or xsl:next-match element contains two or more xsl:with-param elements with matching name attributes.

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 describing the formal parameters of the called template. In this situation, the computed value of the parameter will be validated and/or converted twice, first according to the rules of the as attribute on the xsl:with-param element, and then according to the rules of the as attribute on the xsl:param element.

The focus used for computing the value specified by xsl:with-param element is the same as that used for the xsl:apply-templates, xsl:apply-imports, xsl:next-match, or xsl:call-template element within which it occurs.

[ERR XT0680] In the case of xsl:call-template, it is a static error to pass a parameter named x to a template that does not have a template parameter named x. 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 XT0690] 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 instruction.

[ERR XT0700] In other cases, it is a non-recoverable 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.

Example: A Named Template

This example defines a named template for a numbered-block with an argument 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>

Note:

Arguments to stylesheet functions are supplied as part of an XPath function call: see 10.3 Stylesheet Functions

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 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 6.6 Built-in Template Rules).

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="{$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 = qname
  use-attribute-sets? = qnames>
  <!-- Content: xsl:attribute* -->
</xsl:attribute-set>

[Definition: The xsl:attribute-set element defines a named attribute set: that is, a collection of attribute definitions that can be used repeatedly on different elements in the result tree.]

The required name attribute specifies the name of the attribute set. The value of the name attribute is a QName, which is expanded as described in 5.1 Qualified Names. 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.

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.

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 a QName, 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 a 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.

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 an 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 11.8 Copying Nodes from a Source Tree to a Result Tree.

[ERR XT0710] 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 space-separated sequence of QNames, or if it contains a QName that does not match the name attribute of any xsl:attribute-set declaration in the stylesheet.

[ERR XT0720] 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 XT0730] It is a recoverable dynamic error if the expansion of two or more different xsl:attribute-set declarations with the same name and the same import precedence produce attribute nodes having the same name. The optional recovery action is to include both attribute nodes in the result. When the resulting set of attribute nodes is added to an element node, only the last of the duplicates will take effect.

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.

Attribute sets are used 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.

Example: Using Attribute Sets

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 = qname
  as? = sequence-type
  override? = "yes" | "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 a QName, 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.

[ERR XT0740] A stylesheet function must have a prefixed name, to remove any risk of a clash with a function in the default function namespace. It is a static error if the name has no prefix. The prefix must not refer to a reserved 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 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.

[Definition: The arity of a stylesheet function is the number of xsl:param elements in the function definition.] Optional arguments are not allowed.

[ERR XT0760] 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.

A stylesheet function is included in the in-scope functions of the static context for all XPath expressions used in the stylesheet, unless

  • there is another stylesheet function with the same name and arity, and higher import precedence, or

  • the override attribute has the value no and there is already a function with the same name and arity in the in-scope functions.

The optional override 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 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="yes" ensures interoperable behavior: the same code will execute with all processors. Specifying override="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 to be used in preference to the stylesheet implementation, which is useful when the vendor's implementation is more efficient.

[ERR XT0770] It is a static error for a stylesheet to contain two or more 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.

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. In an XSLT context, the error that occurs when there is no matching function is a dynamic error: this is to allow the stylesheet to execute conditional logic depending on whether or not a function is available, which can be tested using the function-available function.

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.

The optional as attribute indicates the required type of the result of the function. The value of the as attribute is a SequenceType XP, as defined in [XPath 2.0].

[ERR XT0780] If the as attribute is specified, then the result evaluated by the sequence constructor (see 5.6 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.

If a stylesheet function has been defined with a particular expanded-QName, then a call on function-available will return true when called with an argument that is a QName that expands to this same expanded-QName.

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.

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 2.0]. The rules that apply are those for the case where XPath 1.0 compatibility mode is set to false. If the value cannot be converted to the required type, a type exception is signaled. If the as attribute is omitted, no conversion takes place and any value is accepted.

[ERR XT0800] Within the body of a stylesheet function, the focus is initially undefined; this means that any attempt to reference the context item, context position, or context size is a non-recoverable dynamic error.

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.

Example: A Stylesheet Function

The following example creates a 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="2.0"
  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>

11 Creating Nodes and Sequences

This section describes instructions that directly create new nodes, or sequences of nodes and atomic values.

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 18.2 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. 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 5.6 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 5.6.1 Constructing Complex Content

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 permitted values of these attributes and their semantics are described in 19.2 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 5.6.1 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 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 5.6.1 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.

In practice, it makes no difference whether the namespace nodes come before or after the attributes.

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 name 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 xdt: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 xdt: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 xdt:untypedAtomic.

Note:

The xml:base, xml:lang and xml:space 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 these attributes should not be written as attribute value templates: although an XSLT processor will understand this notation, the XML parser will not.

The same is true of the schema-defined attributes xsi:type, xsi:nil, and xsi:schemaLocation. If the stylesheet is processed by a schema processor, these attributes will be recognized and interpreted by the schema processor, but they have no special meaning to the XSLT processor. The attributes are 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 XT0805] 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.

11.1.3 Namespace Nodes for Literal Result Elements

The created element node will also 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 11.1.4 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 18.2 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. It is a static error if there is no namespace bound to the prefix on the element bearing the [xsl:]exclude-result-prefixes attribute.

    The default namespace (as declared by xmlns) may be designated as an excluded namespace by including #default in the list of namespace prefixes.

    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 5.6.3 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 the source tree, specifying the prefix in the [xsl:]exclude-result-prefixes attribute will avoid superfluous namespace declarations in the 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 result tree.

Example: Excluding Namespaces from the Result Tree

For example, consider the following stylesheet:

<xsl:stylesheet xsl: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", although the processor is free to choose a different namespace prefix if it wishes. 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 5.6.3 Namespace Fixup) to introduce a namespace node for this namespace.

11.1.4 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.]

<!-- 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 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 a namespace URI is declared to be an alias for multiple different namespace URIs, then the declaration with the highest import precedence is used.

[ERR XT0810] It is a static error if 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 XT0815] It is a static error if the value #default is specified for either the stylesheet-prefix or the result-prefix attributes of the xsl:namespace-alias element when there is no default namespace.

Note:

See resolution of issue 187. This situation was left unclear in XSLT 1.0.

When a literal result element is processed, its namespace nodes are handled as follows:

  • A namespace node whose string value is a literal namespace URI is not copied to the result tree.

  • A namespace node whose string value is a target namespace URI is copied to the result tree, whether or not the URI identifies an excluded namespace.

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. The processor still has a free choice of prefixes when generating element and attribute names in the result tree, but it will normally use the result-prefix since that prefix will already be declared 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="2.0"
  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="2.0">
    <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="2.0"
  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.

It is not possible to define an alias for the XML namespace http://www.w3.org/XML/1998/namespace because there is a specific provision in [XML Namespaces 1.0] (see erratum NE05) that disallows the use of this namespace URI with any prefix other than xml.

11.2 Creating Element Nodes using xsl:element

<!-- Category: instruction -->
<xsl:element
  name = { qname }
  namespace? = { uri-reference }
  use-attribute-sets? = qnames
  type? = qname
  validation? = "strict" | "lax" | "preserve" | "strip">
  <!-- 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 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 5.6 Sequence Constructors) is used to construct the content of the element, as described in 5.6.1 Constructing Complex Content.

The xsl:element element may have a use-attribute-sets attribute, whose value is a space-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 5.6.1 Constructing Complex Content.

The result of evaluating the xsl:element instruction, except in error cases, is the newly constructed element node.

The name attribute is interpreted as an attribute value template, whose effective value must be a lexical QName.

[ERR XT0820] It is a recoverable dynamic error if the effective value of the name attribute is not a lexical QName. The optional recovery action is to return the sequence of nodes created by evaluating the sequence constructor, excluding any initial attribute and namespace nodes.

[ERR XT0830] In the case of an xsl:element instruction with no namespace attribute, it is a recoverable dynamic error if the effective value of the name attribute is a QName whose prefix is not declared in an in-scope namespace declaration for the xsl:element instruction. The optional recovery action is to ignore the prefix part of the lexical QName, with the effect that the new element will be in the default namespace.

If the namespace attribute is not present then the 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 should be a URI reference. It is not an error if the string is not a syntactically legal URI reference. 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.

Implementations may make use of the prefix of the lexical QName specified in the name attribute when selecting a prefix during the namespace fixup process (see 5.6.3 Namespace Fixup); however, they are not required to do so.

11.2.1 Setting the Type Annotation for a 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 19.2 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.

11.3 Creating Attribute Nodes using xsl:attribute

<!-- Category: instruction -->
<xsl:attribute
  name = { qname }
  namespace? = { uri-reference }
  select? = expression
  separator? = { string }
  type? = qname
  validation? = "strict" | "lax" | "preserve" | "strip">
  <!-- 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 neither is present, the value of the new attribute node will be a zero-length string. The way in which the value is constructed is specified in 5.6.2 Constructing Simple Content.

[ERR XT0840] 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 5.6.2 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 XT0850] It is a recoverable dynamic error if the effective value of the name attribute is not a lexical QName or is the string xmlns. The optional recovery action is to return the empty sequence.

[ERR XT0860] In the case of an xsl:attribute instruction with no namespace attribute, it is a recoverable 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. The optional recovery action is to ignore the prefix part of the QName.

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 should be a URI reference. It is not an error if the string is not a syntactically legal URI reference. 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.

Example: Creating a List-Valued Attribute

The following instruction creates the attribute colors="red green blue":

<xsl:attribute name="colors" select="'red', 'green', 'blue'"/>

Implementations may make use of the prefix of the lexical QName specified in the name attribute when selecting a prefix during the namespace fixup process (see 5.6.3 Namespace Fixup).

Example: Namespaces are not Attributes

It is not an error to write:

<xsl:attribute name="xmlns:xsl" 
   namespace="file://some.namespace">http://www.w3.org/1999/XSL/Transform</xsl:attribute>

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 5.6.1 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 19.2 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.

11.4 Creating Text Nodes

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 4.3 Stripping Whitespace from a Source Tree 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. When the resulting content is added to a result tree, adjacent text nodes in the result tree are merged.

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 20.1 Character Maps) or disable-output-escaping (see 20.2 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 contruct 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 also be empty, in which case the result of evaluating the instruction is an empty sequence.

The result of evaluating an xsl:text instruction is either a single node, the newly constructed text node, or an empty sequence.

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 4.3 Stripping Whitespace from a Source Tree).

For the effect of the deprecated disable-output-escaping attribute, see 20.2 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 compute generated text, for example by extracting text from the source tree or by inserting the value of a variable. The xsl:value-of instruction computes this text using an expression that is specified as the value of the select attribute.

<!-- 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. But if the rules below produce a text node whose string value is the zero-length string, the result of the instruction is an empty sequence.

The string value of the new text node may be defined either by using the select attribute, or by the sequence constructor (see 5.6 Sequence Constructors) that forms the content of the xsl:value-of element. These are mutually exclusive, and one of them must be present. The way in which the value is constructed is specified in 5.6.2 Constructing Simple Content.

[ERR XT0870] 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, or if the select attribute is absent when the content is 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 5.6.2 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 backwards compatible behavior is enabled for the instruction. 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

For example, 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 11.8.2 Deep Copy.

For the effect of the deprecated disable-output-escaping attribute, see 20.2 Disabling Output Escaping

11.5 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 neither is present, 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 5.6.2 Constructing Simple Content.

[ERR XT0880] 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 attribute nodes in the data model, and cannot therefore be constructed using xsl:attribute instructions.

[ERR XT0890] It is a recoverable dynamic error if the effective value of the name attribute is not both an NCName Names and a PITarget XML. The optional recovery action is to return the empty sequence.

Note:

This means that xsl:processing-instruction cannot be used to output an XML declaration. The xsl:output declaration should be used to control this instead (see 20 Serialization).

[ERR XT0900] It is a recoverable dynamic error if the result of evaluating the content of the xsl:processing-instruction contains the string ?>. The optional recovery action is to insert a space after any occurrence of ? that is followed by a >

11.6 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. Since the string value of a namespace node cannot be a zero-length string, one of them must be present. The way in which the value is constructed is specified in 5.6.2 Constructing Simple Content.

[ERR XT0910] 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 5.6.1 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 XT0920] It is a recoverable dynamic error if the effective value of the name attribute is neither a zero-length string nor an NCName Names, or if it is xml or xmlns. The optional recovery action is to return the empty sequence.

[ERR XT0930] It is a recoverable dynamic error if evaluating the select attribute or the contained sequence constructor of an xsl:namespace instruction results in a zero-length string. The optional recovery action is to return the empty sequence.

For details of other error conditions that may arise, see 5.6 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 does, however, constrain the choice of prefixes when namespace fixup is performed.

Namespace prefixes for element and attribute names are effectively established by the namespace fixup process described in 5.6.3 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:

<p:item xmlns:p="p.uri"><xsl:namespace name="p">q.uri</xsl:namespace></p:item>

a possible serialization of the result tree is:

<ns0:item xmlns:ns0="p.uri" xmlns:p="q.uri"/>

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 [XML Namespaces 1.1]). Namespace undeclarations are generated automatically by the serializer if undeclare-namespaces="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.

11.7 Creating Comments

<!-- Category: instruction -->
<xsl:comment
  select? = expression>
  <!-- Content: sequence-constructor -->
</xsl:comment>

The xsl:comment element is evaluated to contruct 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 neither is present, the value of the new comment node will be a zero-length string. The way in which the value is constructed is specified in 5.6.2 Constructing Simple Content.

[ERR XT0940] 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!-->

[ERR XT0950] It is a recoverable dynamic error if the result of evaluating the content of the xsl:comment contains the string -- or ends with -. The optional recovery action is to insert a space after any occurrence of - that is followed by another - or that ends the comment.

11.8 Copying Nodes from a Source Tree to a Result Tree

11.8.1 Shallow Copy

<!-- Category: instruction -->
<xsl:copy
  copy-namespaces? = "yes" | "no"
  use-attribute-sets? = qnames
  type? = qname
  validation? = "strict" | "lax" | "preserve" | "strip">
  <!-- Content: sequence-constructor -->
</xsl:copy>

The xsl:copy instruction provides a way of copying the context item. If the context item is a node, evaluating the xsl:copy instruction constructs a copy of the context 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 context item is an atomic value, the xsl:copy instruction returns this value. The sequence constructor, if present, is not evaluated.

When the context 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. The sequence constructor, if present, is not evaluated.

When the context 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 context node. The content of the new node is formed by evaluating the sequence constructor contained in the xsl:copy instruction. 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 5.6.1 Constructing Complex Content.

Example: Identity Transformation

The identity transformation can be written using xsl:copy as follows:

<xsl:template match="@*|node()">
  <xsl:copy>
    <xsl:apply-templates select="@*|node()"/>
  </xsl:copy>
</xsl:template>

This template rule can be used to copy any node in a tree by applying template rules to its attributes and children. It can be combined with additional template rules that modify selected nodes, for example if all nodes are to be copied except note elements and their contents, this can be achieved by using the identity template rule together with the template rule:

<xsl:template match="note"/>

Note:

The xsl:copy instruction is most useful when copying element nodes. In other cases, the xsl:copy-of instruction is more flexible, because it has a select attribute allowing selection of the nodes or values to be copied.

The xsl:copy instruction has an optional use-attribute-sets attribute, whose value is a space-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 5.6.3 Namespace Fixup.

Note:

Note that 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 5.6.3 Namespace Fixup) when the attribute is added to an element in the result tree, but if namespaces 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 declarations 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 19.2 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. However, if the copied node is subsequently attached as a child to a new element, the final copy of the node inherits its base URI from its parent node, unless this is overridden using an xml:base attribute.

11.8.2 Deep Copy

<!-- Category: instruction -->
<xsl:copy-of
  select = expression
  copy-namespaces? = "yes" | "no"
  type? = qname
  validation? = "strict" | "lax" | "preserve" | "strip" />

The xsl:copy-of instruction can be used to construct a copy of a sequence of nodes and/or atomic values, 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 and atomic values. 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 5.6.3 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.

  • 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 11.8.1 Shallow Copy).

  • If the item is an atomic value, 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 19.2 Validation.

[ERR XT0955] It is a static error to specify copy-namespaces="no" in conjunction with the explicit or implicit value validation="preserve".

Note:

This is because failing to copy the namespace nodes may cause QName values in the content of an element to become invalid.

The base URI of a node is copied. However, if the copied node is subsequently attached as a child to a new element, the final copy of the node inherits its base URI from its parent node, unless this is overridden using an xml:base attribute.

11.9 Constructing Sequences

<!-- Category: instruction -->
<xsl:sequence
  select? = expression
  as? = sequence-type>
  <!-- Content: sequence-constructor -->
</xsl:sequence>

The xsl:sequence instruction may be used within a sequence constructor to construct a sequence of nodes and/or atomic values. This sequence is returned as the result of the instruction. Unlike most other instructions, xsl:sequence can add existing nodes to a sequence, rather than constructing new nodes. When xsl:sequence is used to add atomic values to a sequence, the effect is very similar to the xsl:copy-of instruction.

The items comprising the result sequence may be selected using the select attribute, or constructed using the contained sequence constructor (but not both).

[ERR XT0960] It is a static error if an xsl:sequence instruction with a select attribute has any content other than xsl:fallback instructions.

If the select attribute is omitted and the sequence constructor is empty, the instruction returns an empty sequence.

The as attribute, if present, defines the required type of the result sequence. The computed value of the result sequence will be converted to this type using the function conversion rules.

[ERR XT0970] If the computed value cannot be converted to the required type, a type error occurs.

Note:

The as attribute may be used to restrict the sequence to contain only atomic values, or only nodes, or it may allow a sequence containing both atomic values and nodes.

If no as attribute is specified, the default value is item()*, which permits any value. No conversion then takes place.

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(for $p in //product return
                   if ($p/@price) 
                   then $p/@price 
                   else ($p/@cost * 1.5))"/>

12 Numbering

<!-- Category: instruction -->
<xsl:number
  value? = expression
  select? = expression
  level? = "single" | "multiple" | "any"
  count? = pattern
  from? = pattern
  format? = { string }
  lang? = { nmtoken }
  letter-value? = { "alphabetic" | "traditional" }
  ordinal? = { string }
  grouping-separator? = { char }
  grouping-size? = { number } />

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. But if the formatted number is a zero-length string, the result of the instruction is an empty sequence.

[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 XT0975] 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-number function may be more suitable: see 16.4 Number Formatting.

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 2.0], 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))). The resulting sequence of integers is used as the place marker to be formatted.

If backwards compatible behavior is enabled for the instruction, then all items in the atomized sequence after the first are discarded.

[ERR XT0980] It is a recoverable dynamic error if any undiscarded item in the atomized sequence cannot be converted to an integer, or if the resulting integer is less than 1 (one). The optional recovery action is to convert that item (after atomization, but before conversion to a number) to a string as if by a call to the string FO function and then to insert the resulting string into the formatted result string in its proper position. If the value cannot be converted to a string, the error is treated as an unrecoverable error.

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 XT0990] It is a recoverable dynamic error if the xsl:number instruction is evaluated, with no value or select attribute, when the context item is not a node. The optional recovery action is to return the empty sequence.

[ERR XT1000] 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.

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:

       $A intersect ($F/descendant-or-self::node())

    (this selects $A if it is a descendant-or-self of $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

       $A intersect ($F/descendant-or-self::node())

    (the nodes selected in the first step that are descendant-or-self nodes of 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 that match the count pattern and that precede the selected node in document order, but excluding attribute and namespace nodes)

  • 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 sequence of numbers (the place marker) 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 inserted in the result tree.

Example: Numbing 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:

<xsl:template match="note">
  <fo:block>
     <xsl:number level="any" from="chapter" format="(1) "/>
     <xsl:apply-templates/>
  </fo:block>
</xsl:template>

12.3 Number to String Conversion Attributes

The following attributes are used to control conversion of a sequence of numbers into a string. The numbers are integers greater than 0. 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. 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). If the first token is a non-alphanumeric token, then the constructed string will start with that token; if the last token is non-alphanumeric token, then the constructed string will end with that token. Non-alphanumeric tokens that occur between two format tokens are separator tokens that are used to join numbers in the sequence.

The nth format token will be used to format the nth number in the sequence. If there are more numbers than format tokens, then the last format token will be 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 will be separated from the preceding number by the separator token preceding the format token used to format that number, or, if there are no separator tokens, 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), 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 1 2 ... 10 11 12 ..., and a format token 01 generates the sequence 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 that starts with that token (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 an implementation-defined upper bound on the range of numbers that can be formatted using this format token; indeed, for some numbering sequences there may be an intrinsic limit. For the numbering sequences described above, the upper bound must not be less than 1000 (one thousand). Numbers that exceed the upper bound must be formatted using the format token 1.

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. 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" language="it", if supported, should produce the sequence:

1º 2º 3º 4º ...

The specification format="Ww" ordinal="-o" language="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" language="fr" Un, Deux, Trois, Quatre
German ordinal words format="w" ordinal="-e" language="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 Glassical 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 only 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, xsl:perform-sort, or xsl:sort elements must occur before any other children.

13.1 The xsl:sort Element

<xsl:sort
  select? = expression
  lang? = { nmtoken }
  order? = { "ascending" | "descending" }
  collation? = { uri }
  case-order? = { "upper-first" | "lower-first" }
  data-type? = { "text" | "number" | qname-but-not-ncname }>
  <!-- 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 XT1015] 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).

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, then A will precede B in the sorted sequence if and only if A preceded B in the initial sequence.

Note:

If two items have equal sort key values, 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 data type, 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 data type 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 data type. Any values of type xdt: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 string FO or number FO function as appropriate. If the data-type attribute has any other effective value, then the value must be a lexical QName with a non-empty prefix, and the effect of the attribute is implementation-defined.

[ERR XT1020] 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 evaluated with backwards compatible behavior. With backwards compatible 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) are 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 XT1030] It is a recoverable 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. The optional recovery action is to assign an arbitrary but consistent implementation-dependent ordering to any such pair of values.

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

In general, comparison of two ordinary values is performed according to the rules of the XPath lt operator. However, 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 type and types derived by restriction from xs:string, 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.

[Definition: Facilities in XSLT 2.0 and XPath 2.0 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 implementation-defined.

The one collation URI that must be recognized by every implementation is http://www.w3.org/2003/11/xpath-functions/collation/codepoint, which provides the ability to compare strings based on the Unicode codepoint values of the characters in the string.

For more information about collations, see Section 7.3 Equality and Comparison of StringsFO in [Functions and Operators].

Note:

The reason XSLT does not provide detailed mechanisms for defining collating sequences is that many implementations will re-use collating mechanisms available from the underlying implementation platform (for example, from the operating system or from the run-time library of a chosen programming language). These will inevitably differ from one XSLT implementation to another.

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).

[ERR XT1035] It is a recoverable dynamic error if the collation URI specified to xsl:sort is a collation that is not recognized by the implementation. The optional recovery action is to sort using the collation that would be chosen if the collation attribute were omitted.

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 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 identify 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).

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 5.3.1 Initializing the Static Context.

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.

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 XT1040] 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="xdt:anyAtomicType*">
  <xsl:param name="in" as="xdt: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="element(bib:book)*>
  <xsl:param name="in" as="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

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-values FO 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 Current Group

current-group() as item()*

[Definition: The evaluation context for XPath expressions includes an additional value called the current group, which is a sequence. The current group is the collection of related items that are processed collectively in one iteration of the xsl:for-each-group element.]

While an xsl:for-each-group instruction is being evaluated, the current group will be non-empty. At other times, it will be an empty sequence.

The function current-group returns the current group.

The function takes no arguments.

[ERR XT1060] It is a static error if the current-group function is used within a pattern.

14.2 The Current Grouping Key

current-grouping-key() as xdt:anyAtomicType?

[Definition: The evaluation context for XPath expressions includes an additional value called the current grouping key, which is an atomic value. The current grouping key is a value shared in common by all the items within the current group.]

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. At other times, it will be the empty sequence.

The function current-grouping-key returns the current grouping key.

The function takes no arguments.

[ERR XT1070] It is a static error if the current-grouping-key function is used within a pattern.

14.3 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
  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 node 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. A group is never empty.

[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].

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 XT1080] 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 XT1090] It is an error to specify the collation attribute if neither the group-by attribute nor group-adjacent attribute is specified.

[Definition: If either of the group-by attribute or group-adjacent attributes is present, then grouping keys are calculated for each 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. The resulting sequence is atomized, and each atomic value in the atomized sequence acts as a grouping key for that item in the population.

If the group-by attribute is present, then an item in the population may have multiple grouping keys: that is, the group-by expression evaluates to a sequence. The item is included in as many groups as there are distinct grouping keys (which may be zero). If the group-adjacent attribute is used, then each item in the population must have exactly one grouping key value.

[ERR XT1100] It is a type error if the result of evaluating the group-adjacent attribute is an empty sequence, or a sequence containing more than one item.

Grouping keys are compared using the rules for the eq operator appropriate to their dynamic type. Values of type xdt:untypedAtomic are cast to xs:string before the comparison. Two items that are not comparable using the eq operator are considered to be not equal, that is, they are allocated to different groups. If the values are strings, or untyped atomic values, they are compared using the collation specified in the collation attribute if present, or the default collation otherwise. For the purposes of grouping, the value NaN is considered equal to itself.

[ERR XT1120] When the group-starting-with or group-ending-with attribute is used, it is a type error if the result of evaluating the select expression contains an item that is not a node.

  • 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. For each one of these grouping keys, if there is already a group created to hold items having that grouping key value, J is added 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 assigned to zero, one, or many groups. An item will never be assigned 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 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 assigned 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. In this case, the items in the population must all be nodes.

    The nodes in the population are examined in population order. If a node matches the pattern, or is the first node in the population, then a new group is created and the node becomes its first member. Otherwise, the node is assigned to the same group as its preceding node within the population.

  • If the group-ending-with attribute is present, then its value must be a pattern. In this case, the items in the population must all be nodes.

    The nodes in the population are examined in population order. If a node is the first node in the population, or if the previous node in the population matches the pattern, then a new group is created and the node becomes its first member. Otherwise, the node is assigned to the same group as its preceding node within the population.

[Definition: For each group, the item within the group that is first in population order is known as the initial item of the group.]

[Definition: There is an 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 ordering among groups referred to as processing order.]

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.

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 is the group whose sort key value is being determined, and the current grouping key 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 is the empty sequence.

Example: Sorting Groups in order of their Grouping Key

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())"/>

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 item among the sequence of initial items (one item for each group) arranged in processing order of the groups, the context size is the number of groups, the current group is the group being processed, and the current grouping key 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 is the empty sequence. This has the effect that within the sequence constructor, a call on position() takes successive values 1, 2, ... last().

On completion of the evaluation of the xsl:for-each-group, the current group and current grouping key revert to their previous value.

14.4 Examples of Grouping

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="2.0" 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">
    <tr>
      <td><xsl:value-of select="position()"/></td>
      <td><xsl:value-of select="@country"/></td>
      <td>
        <xsl:value-of select="current-group()/@name" separator=", "/>
      </td>
      <td><xsl:value-of select="sum(current-group()/@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 more flexible solution is to nest one xsl:for-each-group element directly inside another:

<xsl:for-each-group select="cities/city" group-by="@country">
  <xsl:for-each-group select="current-group()" group-by="@name">
    <p><xsl:value-of select="@name"/>, <xsl:value-of select="@country"/>:
        <xsl:value-of select="avg(current-group()/@pop)"/></p>
  </xsl:for-each-group>
</xsl:for-each-group>

The two approaches are not precisely equivalent. If the code were changed to output the value of position() alongside @name then the first approach (a single xsl:for-each-group element with a compound key) would number the groups (1, 2, 3), while the second approach (two nested xsl:for-each-group elements) would number them (1, 2, 1).

 

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 an XML document 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"      >
          <section title="{self::h2}">
            <xsl:for-each select="current-group()[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')]">
    <pageset>
      <xsl:for-each select="current-group()">
        <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">
      <h2><xsl:value-of select="current-grouping-key()"/></h2>
      <xsl:for-each select="current-group()">
        <xsl:value-of select="."/>
      </xsl:for-each>
    </xsl:for-each-group>
</xsl:template>

 

Example: Grouping Alternating Sequences of Elements

In the final 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">
        <xsl:choose>
            <xsl:when test="current-grouping-key()">
                <xsl:copy-of select="current-group()"/>  
            </xsl:when>
            <xsl:otherwise>
                <p>
                    <xsl:copy-of select="current-group()"/>
                </p>
            </xsl:otherwise>  
        </xsl:choose>
    </xsl:for-each-group>
</xsl:template>

15 Regular Expressions

The core function library for XPath 2.0 defines three 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 7.6.1 Regular Expression SyntaxFO), which is itself based on the syntax defined in [XML Schema].

15.1 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).

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 matches FO, replace FO, and tokenize FO. 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 7.6.1.1 FlagsFO).

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}}".

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.

[ERR XT1130] It is a static error if the xsl:analyze-string instruction contains neither an xsl:matching-substring nor an xsl:non-matching-substring element.

The xsl:analyze-string instruction may also have zero or more xsl:fallback child elements. These are ignored by an XSLT 2.0 processor, but allow fallback behavior to be defined when the stylesheet is used with an XSLT 1.0 processor operating in forwards-compatible mode.

This instruction is designed to process all the non-overlapping substrings of the input string that match the regular expression supplied.

[ERR XT1140] It is a non-recoverable 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]. The processor must signal the error. 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 XT1145] It is a non-recoverable dynamic error if the effective value of the flags attribute has a value other than the values defined in [Functions and Operators]. The processor must signal the error. 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 XT1150] It is a non-recoverable dynamic error if the effective value of the regex attribute is a regular expression that matches a zero-length string: or more specifically, if the regular expression $r and flags $f are such that matches("", $r, $f) returns true. The processor must signal the error. 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.

The xsl:analyze-string instruction starts at the beginning of the input string and attempts to find the first substring that matches the regular expression. If there are several matches, the first match is defined to be the one whose starting position comes first in the string. If several alternatives within the regular expression both match at the same 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.

Having found the first match, the instruction proceeds to find the second and subsequent matches by repeating the search, starting at the first character that was not included in the previous match.

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 substring will contain at least one character. This sequence of substrings is processed using the xsl:matching-substring and xsl:non-matching-substring child instructions. 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.

If the input is a zero-length string, the number of substrings will be zero, so neither the xsl:matching-substring nor xsl:non-matching-substring elements will be evaluated.

15.2 Captured Substrings

regex-group($group-number as xs:integer) as xs:string

[Definition: While the xsl:matching-substring instruction is active, a set of current captured substrings is available, corresponding to the parenthized 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.

If the value of the argument is zero, the entire matched string is returned. 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 regular expression does not contain a parenthesized sub-expression with the given number.

  2. The parenthesized sub-expression exists, and did not match any part of the input string.

  3. 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.

15.3 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:non-matching-substring>
    <xsl:value-of select="."/>
  </xsl:non-matching-substring>
  <xsl:matching-substring>
    <br/>
  </xsl: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.

16 Additional Functions

This section describes XSLT-specific additions to the core XPath function library. Some of these additional functions also make use of information specified by declarations in the stylesheet; this section also describes these declarations.

16.1 Multiple Source Documents

document($uri-sequence as item()*) as node()*
document($uri-sequence as item()*, $base-node as node()) as node()*

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 xdt: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 is resolved against a base URI using the rules defined in [RFC2396]

  • 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 xdt: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.

Note:

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.

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 doc FO function defined in [Functions and Operators]. This returns a document node. If an error occurs during evaluation of the doc FO 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 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.

[ERR XT1160] When a URI reference contains a fragment identifier, it is a recoverable 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). The optional recovery action is to ignore the fragment identifier and return the document node. The set of media types recognized by a processor is implementation-defined.

Note:

The recovery action here is different from XSLT 1.0

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.

Note:

The effect of these rules is that unless XML entities or xml:base are used, document("") refers to the document node of the containing stylesheet module (the definitive rules are in [RFC2396]). 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.

16.2 Reading Text Files

unparsed-text($href as xs:string?)  as xs:string
unparsed-text($href as xs:string?, $encoding as xs:string) as xs:string

The unparsed-text function reads an external resource (for example, a file) and returns its contents as a string.

The $href argument must be a string in the form of a URI. The URI must contain no fragment identifier, and must identify a resource that can be read as text. If the URI is a relative URI, then it is resolved relative to the base URI from the static context.

Note:

If a different base URI is appropriate (for example, when resolving a relative URI read from a source document) then the relative URI should be resolved using the resolve-uri FO function before passing it to the unparsed-text function.

The $encoding argument, if present, is the name of an encoding. This encoding is used to translate the contents of the file into a string. The values for this attribute follow the same rules as for the encoding attribute in an XML declaration. The only values which every implementation is obliged to recognize are utf-8 and utf-16.

The encoding of the external resource is determined as follows:

  1. external encoding information is used if available, otherwise

  2. if the media type of the resource is text/xml or application/xml (see [RFC2376]), or if it matches the conventions text/*+xml or application/*+xml (see [RFC3023]), then the encoding is recognized as specified in [XML 1.0], otherwise

  3. the value of the $encoding argument is used if present, otherwise

  4. UTF-8 is assumed.

Note:

The above rules are chosen for consistency with [XInclude]. Files with an XML media type are treated specially because there are use cases for this function where the retrieved text is to be included as unparsed XML within a CDATA section of a containing document, and because processors are likely to be able to reuse the code that performs encoding detection for XML external entities.

[ERR XT1170] It is a recoverable dynamic error if a URI cannot be used to retrieve a resource containing text. The optional recovery action is to treat the URI as if it referenced a resource containing a zero-length string.

[ERR XT1180] It is a recoverable dynamic error if a resource contains characters that are not permitted XML characters. The optional recovery action is to replace each invalid character with the character #xFFFD (Unicode Replacement Character).

Note:

A different character can be substituted in the serialized output by specifying a character map: see 20.1 Character Maps

[ERR XT1190] It is a non-recoverable dynamic error if a resource contains octets that cannot be decoded into permitted XML characters using the specified encoding. This includes the case where the processor does not support the requested encoding.

[ERR XT1200] It is a non-recoverable dynamic error if the second argument of the unparsed-text function is omitted and the processor cannot infer the encoding using external information and the encoding is not UTF-8.

The result is a string containing the text of the resource retrieved using the URI.

Note:

If the text file contains characters such as < and &, these will typically be output as &lt; and &amp; when the string is written to the result tree and serialized as XML or HTML. If these characters actually represent markup (for example, if the text file contains HTML), then the stylesheet can attempt to write them as markup to the output file using the disable-output-escaping attribute of the xsl:value-of instruction (see 20.2 Disabling Output Escaping. Note, however, that implementations are not required to support this feature.

Example: Copying Unparsed HTML Boilerplate

This example attempts to read an HTML file and copy it, as HTML, to the serialized output file:

<xsl:output method="html"/>

<xsl:template match="/">
  <xsl:value-of select="unparsed-text('header.html', 'iso-8859-1')"
                disable-output-escaping="yes"/>
  <xsl:apply-templates/>
  <xsl:value-of select="unparsed-text('footer.html', 'iso-8859-1')"
                disable-output-escaping="yes"/>
</xsl:template>

16.3 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.

16.3.1 The xsl:key Declaration

<!-- Category: declaration -->
<xsl:key
  name = qname
  match = pattern
  use? = expression
  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 a QName, 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.

The value of the key may be specified either using the use attribute or by means of the contained sequence constructor.

[ERR XT1205] 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 the node that matches the pattern as the context node.

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.

[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.]

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 any of 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 that the key specifier in general returns a sequence of values, and any one of these may be used to locate the node.

The optional collation attribute is used only when deciding whether two strings are equal for the purposes of key matching. Specifically, two values $a and $b are considered equal if the result of the function call compare($a, $b, $collation) is zero. If an xsl:key declaration specifies a collation attribute, then every other xsl:key declaration with the same value for its name attribute must either specify the same collation, or specify no collation; this collation is used for all xsl:key declarations with the given name. In the absence of a collation attribute, the default collation is used.

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;

  • a key value that identifies more than one node (the key values for different nodes do not need to be unique).

[Definition: A key is defined as a set of xsl:key declarations in the stylesheet that share the same name.]

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.

[ERR XT1220] It is a static error if there are several xsl:key declarations in the stylesheet with the same key name and different non-defaulted collation attributes. The collation attributes are the same if the URIs consist of the same sequence of Unicode code-points.

16.3.2 The key Function

key($key-name as xs:string, $key-value as xdt:anyAtomicType*) as node*

The key function does for keys what the id FO function does for IDs.

The $key-name argument specifies the name of the key. The value of the argument must be a lexical QName, which is expanded as described in 5.1 Qualified Names.

[ERR XT1260] It is a non-recoverable 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 stylesheet. The processor must signal these errors. 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.

The $key-value argument to the key function is considered as a sequence. The set of requested key values is formed by atomizing the supplied value of the argument, using the standard function calling 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 same document as the context node 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 key declaration when comparing strings. No error is reported if two values are encountered that are not comparable; they are regarded for this 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.

More specifically, the result of the key function is a sequence containing every node N that satisfies the following conditions:

  • N is in the same document as the context node.

  • 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 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.

If the current function is used in either the match pattern or the use expression of the xsl:key declaration, its value is the node N that is being considered for inclusion in the result.

The sequence returned by the key function will be in document order, with duplicates removed.

Example: Using a Key to follow Cross-References

For example, 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.

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>

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 first to change the context node.

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.

[ERR XT1270] It is a non-recoverable dynamic error to call the key function if there is no context node, or if the root of the tree containing the context node is not a document node.

16.4 Number Formatting

format-number($value as xs:double, $picture as xs:string) as xs:string
format-number( $value  as xs:double,
$picture  as xs:string,
$decimal-format-name  as xs:string) as xs:string

The format-number function formats $value as a string using the picture string specified by the $picture argument and the decimal-format named by the $decimal-format-name argument, or the default decimal-format, if there is no $decimal-format-name argument. The value of $decimal-format-name must be a lexical QName, which is expanded as described in 5.1 Qualified Names. The result of the function is the formatted string representation of the supplied number.

[ERR XT1280] It is a recoverable dynamic error if the name specified as the $decimal-format-name argument is not a valid QName, or if its prefix has not been declared in an in-scope namespace declaration, or if the stylesheet does not contain a declaration of a decimal-format with a matching expanded-QName . The optional recovery action is to ignore the $decimal-format-name argument. 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.

16.4.1 Defining a Decimal Format

<!-- Category: declaration -->
<xsl:decimal-format
  name? = qname
  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 />

[Definition: The xsl:decimal-format element declares a decimal-format, which controls the interpretation of a picture string used by the format-number function.] If there is a name attribute, then the element declares a named decimal-format; otherwise, it declares the default decimal-format. The value of the name attribute is a QName, which is expanded as described in 5.1 Qualified Names.

[ERR XT1290] It is a static error to declare either the default decimal-format or a decimal-format with a given name more than once (even with different import precedence), unless it is declared every time with the same value for all attributes (taking into account any default values). If a stylesheet does not contain a declaration of the default 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-number function. An outline of the purpose of each attribute is given below; however, the definitive explanations are given later, as part of the description of this algorithm.

The following attributes control the interpretation of characters in the picture string supplied to the format-number 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.

  • 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.

The following attributes control the interpretation of characters in the picture string supplied to the format-number function. In each case the value must be a single character.

  • 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 XT1300] 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.

16.4.2 Processing the Picture String

[Definition: The formatting of a number is controlled by a picture string. The picture string is a sequence of characters, in which the characters assigned to the variables decimal-separator-sign, grouping-sign, zero-digit-sign, digit-sign and pattern-separator-sign are classified as active characters, and all other characters (including the percent-sign and per-mille-sign) are classified as passive characters.]

The integer part of the sub-picture is defined as the part that appears to the left of the decimal-separator-sign if there is one, or the entire sub-picture otherwise. The fractional part of the sub-picture is defined as the part that appears to the right of the decimal-separator-sign if there is one; it is a zero-length string otherwise.

[ERR XT1310] The picture string must conform to the following rules. It is a recoverable dynamic error if the picture string does not satisfy these rules. The optional recovery action is to ignore those characters in the supplied picture string that make the picture string invalid. If a valid picture string cannot be constructed in this way, the processor may recover by returning the string obtained by applying the string FO function to the supplied number.

Note that in these rules the words "preceded" and "followed" refer to characters anywhere in the string, they are not to be read as "immediately preceded" and "immediately followed".

  • A picture-string consists either of a sub-picture, or of two sub-pictures separated by a pattern-separator-sign. A picture-string must not contain more than one pattern-separator-sign. If the picture-string contains two sub-pictures, the first is used for positive values and the second for negative values.

  • A sub-picture must not contain more than one decimal-separator-sign.

  • A sub-picture must not contain more than one percent-sign or per-mille-sign, and it must not contain one of each.

  • A sub-picture must contain at least one digit-sign or zero-digit-sign.

  • A sub-picture must not contain a passive character that is preceded by an active character and that is followed by another active character.

  • A sub-picture must not contain a grouping-separator-sign adjacent to a decimal-separator-sign.

  • The integer part of a sub-picture must not contain a zero-digit-sign that is followed by a digit-sign. The fractional part of a sub-picture must not contain a digit-sign that is followed by a zero-digit-sign.

The evaluation of the format-number function is described below in two phases, an analysis phase and a formatting phase. The analysis phase takes as its inputs the picture string and the variables derived from the relevant xsl:decimal-format declaration, and produces as its output a number of variables with defined values. The formatting phase takes as its inputs the number to be formatted and the variables produced by the analysis phase, and produces as its output a string containing a formatted representation of the number.

Note:

Numbers will always be formatted with the most significant digit on the left.

16.4.3 Analysing the Picture String

This phase of the algorithm analyses the picture string and the attribute settings of the xsl:decimal-format declaration, and has the effect of setting the values of various variables, which are used in the subsequent formatting phase. These variables are listed below. Each is shown with its initial setting and its data type.

Several variables are associated with each sub-picture. If there are two sub-pictures, then these rules are applied to one sub-picture to obtain the values that apply to positive numbers, and to the other to obtain the values that apply to negative numbers. If there is only one sub-picture, then the values for both cases are derived from this sub-picture.

The variables are as follows:

  • The whole-part-grouping-positions is a sequence of integers representing the positions of grouping separators within the integer part of the sub-picture. For each grouping-separator-sign that appears within the integer part of the sub-picture, this sequence contains an integer that is equal to the total number of digit-sign and zero-digit-sign characters that appear within the integer part of the sub-picture and to the right of the grouping-separator-sign. In addition, if these whole-part-grouping-positions are at regular intervals (that is, if they are all consecutive integer multiples of some value N, including the case where there is only one number in the list), then the sequence contains all integer multiples of N as far as necessary to accommodate the largest possible number.

  • The minimum-whole-part-size is an integer indicating the minimum number of digits that will appear to the left of the decimal-separator-sign. It is normally set to the number of zero-digit-sign characters found in the integer part of the sub-picture. But if the sub-picture contains no zero-digit-sign and no decimal-separator-sign, it is set to one.

  • The overflow-threshold indicates the smallest number that is too large to fit in the space available. If any digit-sign is found in the integer part of the sub-picture, the overflow-threshold is set to infinity. Otherwise, it is set to ten raised to the power of the number of zero-digit-sign characters found in the integer part of the sub-picture.

  • The prefix is set to contain all passive characters in the sub-picture to the left of the leftmost active character. If the picture string contains only one sub-picture, the prefix for the negative sub-picture is set by concatenating the minus-sign character and the prefix for the positive sub-picture (if any), in that order.

  • The fractional-part-grouping-positions is a sequence of integers representing the positions of grouping separators within the fractional part of the sub-picture. For each grouping-separator-sign that appears within the fractional part of the sub-picture, this sequence contains an integer that is equal to the total number of digit-sign and zero-digit-sign characters that appear within the fractional part of the sub-picture and to the left of the grouping-separator-sign.

  • The minimum-fractional-part-size is set to the number of zero-digit-sign characters found in the fractional part of the sub-picture.

  • The maximum-fractional-part-size is set to the total number of digit-sign and zero-digit-sign characters found in the fractional part of the sub-picture.

  • The suffix is set to contain all passive characters to the right of the rightmost active character in the fractional part of the sub-picture.

Note:

If there is only one sub-picture, then all variables for positive numbers and negative numbers will be the same, except for prefix: the prefix for negative numbers will be preceded by the minus-sign character.

16.4.4 Formatting the Number

This section describes the second phase of processing of the format-number function. This phase takes as input a number to be formatted (referred to as the input number), and the variables set up by analysing the xsl:decimal-format declaration and the picture string, as described above. The result of this phase is a string, which forms the return value of the format-number function.

The algorithm for this second stage of processing is as follows:

  1. If the input number is NaN (not a number), the result is the concatenation of the prefix, the specified NaN-symbol, and the suffix, where the prefix and suffix are taken from the sub-picture that applies to positive numbers.

  2. In the rules below, the positive sub-picture and its associated variables are used if the input number is positive, and the negative sub-picture and its associated variables are used otherwise. Negative zero is taken as negative, positive zero as positive.

  3. If the input number is positive or negative infinity, the result is the concatenation of the appropriate prefix, the infinity-symbol, and the appropriate suffix.

  4. If the sub-picture contains a percent-sign, the number is multiplied by 100. If the sub-picture contains a per-mille-sign, the number is multiplied by 1000. The resulting number is referred to below as the adjusted number.

  5. [ERR XT1320] It is a recoverable dynamic error if the absolute value of the adjusted number is numerically greater than or equal to the overflow-threshold. The optional recovery action is to format the number as if each zero-digit-sign character in the integer part of the sub-picture were a digit-sign.

  6. The adjusted number is rounded so that it uses no more than maximum-fractional-part-size digits in its fractional part. The rounded number is defined as the result of calling the function round-half-to-evenFO with the adjusted number as the first argument, and the maximum-fractional-part-size as the second argument.

  7. The absolute value of the rounded number is converted to a string in decimal notation, with no insignificant leading or trailing zeroes, using the characters implied by the choice of zero-digit-sign to represent the ten decimal digits, and the decimal-separator-sign to separate the integer part and the fractional part. (The value zero will at this stage be represented by a decimal-separator-sign on its own.)

  8. If the number of digits to the left of the decimal-separator-sign is less than minimum-whole-part-size, leading zero-digit-sign characters are added to pad out to that size.

  9. If the number of digits to the right of the decimal-separator-sign is less than minimum-fractional-part-size, trailing zero-digit-sign characters are added to pad out to that size.

  10. For each integer N in the whole-part-grouping-positions list, a grouping-separator-sign character is inserted into the string immediately after that digit that appears in the integer part of the number and has N digits between it and the decimal-separator-sign, if there is such a digit.

  11. For each integer N in the fractional-part-grouping-positions list, a grouping-separator-sign character is inserted into the string immediately before that digit that appears in the fractional part of the number and has N digits between it and the decimal-separator-sign, if there is such a digit.

  12. If there is no decimal-separator-sign in the sub-picture, the decimal-separator-sign character is removed from the string (it will be the rightmost character in the string).

  13. The result of the function is the concatenation of the appropriate prefix, the string conversion of the number as obtained above, and the appropriate suffix.

16.5 Formatting Dates and Times

Three functions are provided to represent dates and times as a string, using the conventions of a selected calendar, language, and country. Each has two variants.

format-dateTime( $value  as xs:dateTime?,
$picture  as xs:string,
$language  as xs:string?,
$calendar  as xs:string?,
$country  as xs:string?) as xs:string?
format-dateTime($value as xs:dateTime?, $picture as xs:string) as xs:string?
format-date( $value  as xs:date?,
$picture  as xs:string,
$language  as xs:string?,
$calendar  as xs:string?,
$country  as xs:string?) as xs:string?
format-date($value as xs:date?, $picture as xs:string) as xs:string?
format-time( $value  as xs:time?,
$picture  as xs:string,
$language  as xs:string?,
$calendar  as xs:string?,
$country  as xs:string?) as xs:string?
format-time($value as xs:time?, $picture as xs:string) as xs:string?

The format-dateTime, format-date, and format-time functions format $value as a string using the picture string specified by the $picture argument, the calendar specified by the $calendar argument, the language specified by the $language argument, and the country specified by the $country argument. The result of the function is the formatted string representation of the supplied dateTime, date, or time value.

[Definition: The three functions format-date, format-time, and format-dateTime are referred to collectively as the date formatting functions.]

If $value is the empty sequence, the empty sequence is returned.

Calling the two-argument form of each of the three functions is equivalent to calling the five-argument form with each of the last three arguments set to an empty sequence.

For details of the language, calendar, and country arguments, see 16.5.2 The language, calendar, and country arguments.

In general, the use of an invalid picture, language, calendar, or country argument is classified as a recoverable dynamic error, with the optional recovery action being to output the value of the date, time, or dateTime in a fallback representation. Use of an option in any of these arguments that is valid but not supported by the implementation is not an error, and in these cases the implementation is required to output the value in a fallback representation.

16.5.1 The Picture String

The picture consists of a sequence of variable markers and literal substrings. A substring enclosed in square brackets is interpreted as a variable marker; substrings not enclosed in square brackets are taken as literal substrings. The literal substrings are optional and if present are rendered unchanged, including any whitespace. If an opening or closing square bracket is required within a literal sub-string, it must be doubled. The variable markers are replaced in the result by strings representing aspects of the date and/or time to be formatted. These are described in detail below.

A variable marker consists of a component specifier followed optionally by one or two presentation modifiers and/or optionally by a width modifier. Whitespace within a variable marker is ignored.

The component specifier indicates the component of the date or time that is required, and takes the following values:

Specifier Meaning Default Presentation Modifier
Y year 1
M month in year 1
D day in month 1
d day in year 1
F day of week n
W week in year 1
w week in month 1
H hour in day (24 hours) 1
h hour in half-day (12 hours) 1
P am/pm marker n
m minute in hour 1
s second in minute 1
f fractional seconds 1
Z timezone as a time offset from UTC, or if an alphabetic modifier is present the conventional name of a timezone (such as PST) 1
z timezone as a time offset using GMT, for example GMT+1 1
C calendar: the name or abbreviation of a calendar name n
E era: the name of a baseline for the numbering of years, for example the reign of a monarch n

[ERR XT1350] It is a recoverable dynamic error if a component specifier within the picture refers to components that are not available in the given $value. The optional recovery action is to ignore the offending component specifiers.

The first presentation modifier indicates the style in which the value of a component is to be represented. Its value may be either:

  • any format token permitted in the format string of the xsl:number instruction (see 12 Numbering), indicating that the value of the component is to be output numerically using the specified number format (for example, 1, 01, i, I, w, W, or Ww) or

  • the format token n, N, or Nn, indicating that the value of the component is to be output by name, in lower-case, upper-case, or title-case respectively. Components that can be output by name include (but are not limited to) months, days of the week, timezones, and eras.

If the implementation does not support the use of the requested format token, it must use the default presentation modifier for that component.

If the first presentation modifier is present, then it may optionally be followed by a second presentation modifier as follows:

Modifier Meaning
t traditional numbering. This has the same meaning as letter-value="traditional" in xsl:number.
o ordinal form of a number, for example 8th or . The actual representation of the ordinal form of a number may depend not only on the language, but also on the grammatical context (for example, in some languages it must agree in gender).

Note:

Although the formatting rules are expressed in terms of the rules for format tokens in xsl:number, the formats actually used may be specialized to the numbering of date components where appropriate. For example, in Italian, it is conventional to use an ordinal number (primo) for the first day of the month, and cardinal numbers (due, tre, quattro ...) for the remaining days. A processor may therefore use this convention to number days of the month, ignoring the presence or absence of the ordinal presentation modifier.

Whether or not a presentation modifier is included, a width modifier may be supplied. This indicates the number of characters or digits to be included in the representation of the value.

The width modifier, if present, is introduced by a comma. It takes the form:

   ,  min-width ("-" max-width)?

where min-width is either an unsigned integer indicating the minimum number of characters to be output, or * indicating that there is no explicit minimum, and max-width is either an unsigned integer indicating the maximum number of characters to be output, or * indicating that there is no explicit maximum; if max-width is omitted then * is assumed. Both integers, if present, must be greater than zero.

A format token containing leading zeroes, such as 001, sets the minimum and maximum width to the number of digits appearing in the format token; if a width modifier is also present, then the width modifier takes precedence.

If the minumum and maximum width are unspecified, then the output uses as many characters as are required to represent the value of the component without truncation and without padding: this is referred to below as the full representation of the value.

If the full representation of the value exceeds the specified maximum width, then the processor should attempt to use an alternative shorter representation that fits within the maximum width. Where the presentation modifier is N, n, or Nn, this is done by abbreviating the name, using either conventional abbreviations if available, or crude right-truncation if not. For example, setting max-width to 4 indicates that four-letter abbreviations should be used, though it would be acceptable to use a three-letter abbreviation if this is in conventional use. (For example, "Tuesday" might be abbreviated to "Tues", and "Friday" to "Fri".) In the case of the year component, setting max-width requests omission of high-order digits from the year, for example, if max-width is set to 2 then the year 2003 will be output as 03. If no mechanism is available for fitting the value within the specified maximum width (for example, when roman numerals are used), then the value should be output in its full representation.

If the full representation of the value is shorter than the specified minimum width, then the processor should pad the value to the specified width. For decimal representations of numbers, this should be done by prepending zero digits from the appropriate set of digit characters, or appending zero digits in the case of the fractional seconds component. In other cases, it should be done by appending spaces.

16.5.2 The language, calendar, and country arguments

The set of languages, calendars, and countries that are supported in the date formatting functions is implementation-defined. When any of these arguments is omitted or is an empty sequence, an implementation-defined default value is used.

If the fallback representation uses a different calendar from that requested, the output string must be prefixed with [Calendar: X] where X identifies the calendar actually used. The string Calendar should be localized using the requested language if available. If the fallback representation uses a different language from that requested, the output string should be prefixed with [Language: Y] where Y identifies the language actually used. The string Language may be localized in an implementation-dependent way. If a particular component of the value cannot be output in the requested format, it should be output in the default format for that component.

The language argument specifies the language to be used for the result string of the function. The value of the argument must be either the empty sequence or a value that would be valid for the xml:lang attribute (see [XML]). Note that this permits the identification of sublanguages based on country codes (from [ISO 3166-1]) as well as identification of dialects and of regions within a country.

If the language argument is omitted or is set to an empty sequence, or if it is set to an invalid value or a value that the implementation does not recognize, then the processor uses implementation-defined language. If an explicit language was requested and the request is not honored,

The language is used to select the appropriate language-dependent forms of:

names (for example, of months)
numbers expressed as words or as ordinals (twenty, 20th, twentieth)
hour convention (0-23 vs 1-24, 0-11 vs 1-12)
first day of week, first week of year

Where appropriate this choice may also take into account the value of the country argument, though this should not be used to override the language or any sublanguage that is specified as part of the language argument.

The choice of the names and abbreviations used in any given language is implementation-defined. For example, one implementation might abbreviate July as Jul while another uses Jly. In German, one implementation might represent Saturday as Samstag while another uses Sonnabend. Implementations may provide mechanisms allowing users to control such choices.

Where ordinal numbers are used, the selection of the correct representation of the ordinal (for example, the linguistic gender) may depend on the component being formatted and on its textual context in the picture string.

The calendar attribute specifies that the dateTime, date, or time supplied in the $value argument must be converted to a value in the specified calendar and then converted to a string using the conventions of that calendar.

A calendar value must be a valid QName. If the QName does not have a prefix, then it identifies a calendar with the designator specified below. If the QName has a prefix, then the QName is expanded into an expanded-QName as described in 5.1 Qualified Names; the expanded-QName identifies the calendar; the behavior in this case is implementation-defined.

If the calendar attribute is omitted an implementation-defined value is used.

Note:

The calendars listed below were known to be in use during the last hundred years. Many other calendars have been used in the past.

This specification does not define any of these calendars, nor the way that they map to the value space of the xs:date data type in [XML Schema]. There may be ambiguities when dates are recorded using different calendars. For example, the start of a new day is not simultaneous in different calendars, and may also vary geographically (for example, based on the time of sunrise or sunset). Translation of dates is therefore more reliable when the time of day is also known, and when the geographic location is known. When translating dates between one calendar and another, the processor may take account of the values of the country and/or language arguments, with the country argument taking precedence.

Information about some of these calendars, and algorithms for converting between them, may be found in [Calendrical Calculations].

Designator Calendar
AD Anno Domini (Christian Era)
AH Anno Hegirae (Muhammedan Era)
AME Mauludi Era (solar years since Mohammed's birth)
AM Anno Mundi (Jewish Calendar)
AP Anno Persici
AS Aji Saka Era (Java)
BE Buddhist Era
CB Cooch Behar Era
CE Common Era
CL Chinese Lunar Era
CS Chula Sakarat Era
EE Ethiopian Era
FE Fasli Era
ISO ISO 8601 calendar
JE Japanese Calendar
KE Khalsa Era (Sikh calendar)
KY Kali Yuga
ME Malabar Era
MS Monarchic Solar Era
NS Nepal Samwat Era
OS Old Style (Julian Calendar)
RS Rattanakosin (Bangkok) Era
SE Saka Era
SH Mohammedan Solar Era (Iran)
SS Saka Samvat
TE Tripurabda Era
VE Vikrama Era
VS Vikrama Samvat Era

At least one of the above calendars must be supported. It is implementation-defined which calendars are supported.

The ISO 8601 calendar ([ISO 8601]), which is included in the above list and designated ISO, is essentially the same as the Gregorian calendar designated AD, but it prescribes the use of particular numbering conventions as defined in ISO 8601, rather than allowing these to be localized on a per-language basis. Specifically, in the ISO calendar the days of the week are numbered from 1 (Monday) to 7 (Sunday), and week 1 in any calendar year is the week (from Monday to Sunday) that includes the first Thursday of that year. The numeric values of the components year, month, day, hour, minute, and second are the same in this calendar as the values used in the lexical representation of the date and time as defined in [XML Schema]. The ISO calendar is intended primarily for applications that need to produce dates and times in formats to be read by other software, rather than by human users.

Note:

The value space of the date and time data types, as defined in XML Schema, is based on absolute points in time. The lexical space of these data types defines a representation of these absolute points in time using the proleptic Gregorian calendar, that is, the modern Western calendar extrapolated into the past and the future; but the value space is calendar-neutral. The date formatting functions produce a representation of this absolute point in time, but denoted in a possibly different calendar. So, for example, the date whose lexical representation in XML Schema is 1502-01-11 (the day on which Pope Gregory XIII was born) might be formatted using the Old Style (Julian) calendar as 1 January 1502. This reflects the fact that there was at that time a ten-day difference between the two calendars. It would be incorrect, and would produce incorrect results, to represent this date in an element or attribute of type xs:date as 1502-01-01, even though this might reflect the way the date was recorded in contemporary documents.

The intended use of the country argument is to identify the place where an event represented by the dateTime, date, or time supplied in the $value argument took place or will take place. If the value is supplied, and is not the empty sequence, then it should be a country code defined in [ISO 3166-1]. Implementations may also allow the use of codes representing subdivisions of a country from ISO 3166-2, or codes representing formerly used names of countries from ISO 3166-3. This argument is not intended to identify the location of the user for whom the date or time is being formatted; that should be done by means of the language attribute. This information may be used to provide additional information when converting dates between calendars or when deciding how individual components of the date and time are to be formatted. For example, different countries using the Old Style (Julian) calendar started the new year on different days, and some countries used variants of the calendar that were out of sychronization as a result of differences in calculating leap years. The geographical area identified by an ISO 3166-1 country code is defined by the present-day boundaries of that country, not by the boundaries as they existed historically.

16.5.3 Examples of date and time formatting

Example: Gregorian Calendar

The following examples show a selection of dates and times and the way they might be formatted. These examples assume the use of the Gregorian calendar as the default calendar.

Required Output Expression
2002-12-31 format-date($d, "[Y0001]-[M01]-[D01]")
12-31-2002 format-date($d, "[M]-[D]-[Y]")
31-12-2002 format-date($d, "[D]-[M]-[Y]")
31 XII 2002 format-date($d, "[D1] [MI] [Y]")
31st December, 2002 format-date($d, "[D1o] [MNn], [Y]", "en", (), ())
31 DEC 2002 format-date($d, "[D01] [MN,*-3] [Y0001]", "en", (), ())
December 31, 2002 format-date($d, "[MNn] [D], [Y]", "en", (), ())
31 Dezember, 2002 format-date($d, "[D] [MNn], [Y]", "de", (), ())
Tisdag 31 December 2002 format-date($d, "[FNn] [D] [MNn] [Y]", "sv", (), ())
[2002-12-31] format-date($d, "[[[Y0001]-[M01]-[D01]]]")
Two Thousand and Three format-date($d, "[YWw]", "en", (), ())
einunddreißigste Dezember format-date($d, "[Dwo] [MNn]", "de", (), ())
3:58 PM format-time($t, "[h]:[m01] [PN]", "en", (), ())
3:58:45 pm format-time($t, "[h]:[m01]:[s01] [Pn]", "en", (), ())
3:58:45 PM PDT format-time($t, "[h]:[m01]:[s01] [PN] [ZN,*-3]", "en", (), ())
3:58:45 o'clock PM PDT format-time($t, "[h]:[m01]:[s01] o'clock [PN] [ZN,*-3]", "en")
15:58 format-time($t,"[H01]:[m01]")
15:58:45.762 format-time($t,"[H01]:[m01]:[s01].[f001]")
15:58:45 GMT+02:00 format-time($t,"[H01]:[m01]:[s01] [z]", "en", (), ())
15.58 Uhr GMT+02:00 format-time($t,"[H01]:[m01] Uhr [z]", "de", (), ())

 

Example: Non-Gregorian Calendars

The following examples use calendars other than the Gregorian calendar.

These examples use non-Latin characters which might not display correctly in all browsers, depending on the system configuration.

Description Request Result
Islamic format-date($d, "[D&#x0661;] [Mn] [Y&#x0661;]", "Islamic", "ar", "AH", ()) ٢٦ ﺸﻭّﺍﻝ ١٤٢٣
Jewish (with Western numbering) format-date($d, "[D] [Mn] [Y]", "he", "AM", ()) ‏26 טבת 5763
Jewish (with traditional numbering) format-date($d, "[D&#x05D0;t] [Mn] [Y&#x05D0;t]", "he", "AM", ()) כ״ו טבת תשס״ג
Julian (Old Style) format-date($d, "[D] [MNn] [Y]", "en", "OS", ()) 18 December 2002
Thai format-date($d, "[D&#x0E51;] [Mn] [Y&#x0E51;]", "th", "BE", ()) ๓๑ ธันวาคม ๒๕๔๕

16.6 Miscellaneous Additional Functions

16.6.1 current

current() as item()

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.

Example: Using the current Function

For example,

<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.

If the current function is used within a pattern, its value is the node that is being matched against the pattern.

[ERR XT1360] If the current function is evaluated within an expression that is evaluated when the context item is undefined, a non-recoverable dynamic error occurs.

16.6.2 unparsed-entity-uri

unparsed-entity-uri($entity-name as xs:string) as xs:string

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 string if there is no such entity. This function maps to the dm:unparsed-entity-system-id accessor defined in [Data Model].

[ERR XT1370] It is a non-recoverable dynamic error if the unparsed-entity-uri is called when there is no context node, or when the root of the tree containing the context node is not a document node.

16.6.3 unparsed-entity-public-id

unparsed-entity-public-id($entity-name as xs:string) as xs:string

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].

[ERR XT1380] It is a non-recoverable dynamic error if the unparsed-entity-public-id is called when there is no context node, or when the root of the tree containing the context node is not a document node.

16.6.4 generate-id

generate-id() as xs:string
generate-id($node as node()?) as xs:string

The generate-id function returns a string that uniquely identifies a given node. The unique identifier must consist of ASCII alphanumeric characters and must start with an alphabetic character. Thus, the string is syntactically an XML name. An implementation is free to generate an identifier in any convenient way provided that it always generates the same identifier for the same node and that different identifiers are always generated from different nodes. An implementation is under no obligation to generate the same identifiers each time a document is transformed. There is no guarantee that a generated unique identifier will be distinct from any unique IDs specified in the source document. If the argument is the empty sequence, the result is the zero-length string. If the argument is omitted, it defaults to the context node.

16.6.5 system-property

system-property($property-name as xs:string) as xs:string

The $property-name argument must evaluate to a lexical QName. The lexical QName is expanded as described in 5.1 Qualified Names.

[ERR XT1390] It is a non-recoverable 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. The processor must signal these errors. 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.

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 "2.0". The value will always be a string in the lexical space of the decimal data type defined in XML Schema (see [XML Schema]) 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 backwards compatibility feature, or "no" otherwise.

Some of these properties relate to the conformance levels and features offered by the processor: these options are described in 21 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.

Note:

An implementation must not return the value 2.0 as the value of the xsl:version system property unless it is conformant to XSLT 2.0.

It is recognized that vendors who are enhancing XSLT 1.0 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 2.0, 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 2.0, and to provide the element-available and function-available functions to allow users to test which features have been fully implemented.

Implementations must not define additional system properties in the XSLT namespace.

17 Messages

<!-- Category: instruction -->
<xsl:message
  select? = expression
  terminate? = { "yes" | "no" }>
  <!-- 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 5.6.1 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 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 terminate processing after sending the message. 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.

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>

18 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 the XPath specification, an additional function defined in this XSLT specification, 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.

18.1 Extension Functions

If the function name used in a FunctionCall XP within an XPath expression is not an NCName Names (that is, if it contains a colon), and if the stylesheet contains no stylesheet function with a matching expanded-QName, then it is treated as a call to an extension function. The QName used as the function name is expanded using the namespace declarations in scope at the point in the stylesheet where the expression appears.

18.1.1 Testing Availability of Functions

The function-available function can be used with the xsl:choose and xsl:if instructions to explicitly control how a stylesheet behaves if a particular extension function is not available.

function-available($function-name as xs:string) as xs:boolean

A function name is said to be available if it matches the name of a core function defined in XPath, or the name of an additional function defined in this XSLT specification, or the name of a stylesheet function, or if the processor is able to locate an implementation of an extension function with a matching name.

The function-available function returns true if the function name supplied as its $function-name argument is available; otherwise it returns false.

The value of the $function-name argument must be a string containing a lexical QName. The lexical QName is expanded into an expanded-QName using the namespace declarations in scope for the expression. If the lexical QName is unprefixed, then the standard function namespace is used in the expanded QName. The function-available function returns true if and only if the expanded-QName is the name of a function in the function library. If the expanded-QName has a non-null namespace URI, then it refers to a stylesheet function or extension function; otherwise, it refers to a function defined by XPath or XSLT.

[ERR XT1400] It is a recoverable dynamic error if the argument does not evaluate to a string that is a valid QName, or if there is no namespace declaration in scope for the prefix of the QName. The optional recovery action is to return the value false. 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.

Note:

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 number of arguments expected, nor their types.

[ERR XT1410] It is a non-recoverable dynamic error if a FunctionCall XP within an XPath expression is evaluated, when the function in question is not available. An implementation must not signal a static error merely because an expression contains a call to an extension function for which no implementation is available.

18.1.2 Calling Extension Functions

If the function name used in a FunctionCall XP within an XPath expression identifies an extension function, then to evaluate the FunctionCall XP, the processor will first evaluate each of the arguments in the FunctionCall XP. If the processor has information about the data types expected by the extension function, then it may perform any necessary type conversions between the XPath data types 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 data types of the implementation language and those of XPath. The details of such type conversions are outside the scope of this specification.

[ERR XT1420] It is a non-recoverable 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:

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.

18.1.3 External Objects

An implementation may allow an extension function to return an object that does not have any natural representation in the XPath data model, either as an atomic value or as a node. 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 data type, or they might be mapped to existing data types such as integer, string, or anyURI.

18.2 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 3.6.1 User-defined Data Elements) are not extension elements as defined here, and nothing in this section applies to them.

18.2.1 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 attributes is a whitespace-separated list of namespace prefixes. The namespace bound to each of the prefixes is designated as an extension namespace.

[ERR XT1430] It is a static error if there is no namespace bound to the prefix on the element bearing the [xsl:]extension-element-prefixes attribute. The default namespace (as declared by xmlns) may be designated as an extension namespace by including #default in the list of namespace prefixes. 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.

18.2.2 Testing Availability of Instructions

The element-available function can be used with the xsl:choose and xsl:if instructions to explicitly control how a stylesheet behaves if a particular extension instruction is not available.

element-available($element-name as xs:string) as xs:boolean

The value of the $element-name argument must be a string containing a QName. The QName is expanded into an expanded-QName using the namespace declarations in scope for the expression. If there is a default namespace in scope, then it is used to expand an unprefixed QName. The element-available function returns true if and only if the expanded-QName is the name of an instruction. If the expanded-QName has a namespace URI equal to the XSLT namespace URI, then it refers to an element defined by XSLT. Otherwise, it refers to an extension instruction. If the expanded-QName has a null namespace URI, the element-available function will return false.

[ERR XT1440] It is a recoverable dynamic error if the argument does not evaluate to a string that is a valid QName, or if there is no namespace declaration in scope for the prefix of the QName. The optional recovery action is to return the value false. 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.

If the processor does not have an implementation of a particular extension instruction available, then the element-available function must return false for the name of the element. When such an extension instruction is evaluated, then the processor must perform fallback for the element as specified in 18.2.3 Fallback. An implementation must not signal an error merely because the stylesheet contains an extension instruction for which no implementation is available.

If the processor has an implementation of a particular extension instruction available, then the element-available function must return true for the name of the element.

18.2.3 Fallback

<!-- Category: instruction -->
<xsl:fallback>
  <!-- Content: sequence-constructor -->
</xsl:fallback>

[ERR XT1450] When a processor performs fallback for an instruction element, 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 non-recoverable dynamic error if it has no xsl:fallback children.

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 2.0, 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.

19 Result Trees

The output of a transformation is a set of zero or more result trees.

A result tree may be created explicitly, by evaluating an xsl:result-document instruction. A result tree is also created implicitly if the result of evaluating the initial template is a non-empty sequence. This implicit result tree is created as if the sequence constructor contained in the initial template were contained in an xsl:result-document instruction with no attributes.

The way in which a result tree is delivered to an application is implementation-defined.

A result tree has a URI. If the implementation provides an API to access result trees, then it must allow a final result tree to be identified by means of this URI.

Note:

The URI of the result tree is not the same thing as the URI of its serialized representation on disk, if any. For example, a server (or browser client) might store the result trees only in memory, or in an internal disk cache. As long as it 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 result tree contains links to another result tree produced during the same transformation, in the form of a relative URI. 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.

Note:

The URI of a result tree is unrelated to the base URI of its document node.

Serialization of final result trees is described further in 20 Serialization

19.1 Creating Result Trees

<!-- Category: instruction -->
<xsl:result-document
  format? = qname
  href? = { uri-reference }
  validation? = "strict" | "lax" | "preserve" | "strip"
  type? = qname>
  <!-- Content: sequence-constructor -->
</xsl:result-document>

The xsl:result-document instruction is used to create a 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 5.6.1 Constructing Complex Content. The tree rooted at this document node forms the 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 value of the format attribute, if specified, must be a QName. The QName is expanded using the namespace declarations in scope for the xsl:result-document element. The 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 result tree (see 20 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 XT1460] It is a static error if the value of the format attribute is not a valid QName, or if it does not match the expanded-QName of an output definition in the stylesheet.

The href attribute is optional. The default value is the zero-length string. The effective value of the attribute must be a URI, 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 legal relative URI must be accepted. Note that the zero-length string is a legal relative URI.

If the effective value is a relative URI, then it is resolved relative to the base output URI.

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 result tree will carry. The permitted values and their semantics are described in 19.2.2 Validating Document Nodes.

A processor may allow a result tree to be serialized. Serialization is described in 20 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 result trees. An implementation that does not support the serialization of result trees may ignore the format attribute. Such an implementation must provide the application with some means of access to the (un-serialized) result tree, optionally using its URI to identify it.

Implementations may provide additional mechanisms, outside the scope of this specification, for defining the way in which 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="2.0"
        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].

[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:attribute, xsl:comment, xsl:processing-instruction, xsl:namespace, xsl:value-of, xsl:function, xsl:key, xsl:sort, and xsl:message always evaluate the instructions in their contained sequence constructor in temporary output state.

[ERR XT1480] It is a non-recoverable dynamic error to evaluate the xsl:result-document instruction in temporary output state.

[ERR XT1490] It is a non-recoverable dynamic error for a transformation to generate two or more 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 the initial result tree is created implicitly.

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 XT1500] It is a recoverable dynamic error for a stylesheet to write to an external resource and read from the same resource during a single transformation, whether or not the same URI is used to access the resource in both cases. The optional recovery action is implementation-dependent: implementations are not obliged to detect the error condition.

19.2 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, and xsl:result-document instructions, or the xsl:type and xsl:validation attributes of a literal result element.

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 default-validation attribute of the containing xsl:stylesheet element; if this is not specified, the effect is the same as specifying validation="strip".

[ERR XT1505] 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, 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 19.2.1 Validating Constructed Elements and Attributes, while those for document nodes are given in 19.2.2 Validating Document Nodes.

19.2.1 Validating Constructed Elements and Attributes

The [xsl:]validation attribute defines the action to be taken. It determines the type annotation not only 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 xdt:untypedAny.

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 xdt:untypedAny if it is an element, or xdt: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 discarded. 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 xdt:untypedAny in the case of elements, or xdt: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 xdt:untypedAny, 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 xdt:untypedAtomic.

    • In the case of xsl:copy-of, all the nodes that are copied will retain their type annotations unchanged. This option is permitted only if all namespace nodes are retained.

    • 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 xdt:untypedAny (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, an 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). 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 the element is not considered valid, the transformation fails. 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.

    • In the case of an attribute, an 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. 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 permitted by [XML Schema] (see Part 1, section 4.3.2, How schema documents are located on the Web). The components in the schema constructed from the synthetic schema document (see 3.13 Importing Schema Components) will always be available for validating constructed nodes; if additional schema components are needed, they may for example be located implicitly from knowledge of the namespace in which the elements and attributes appear, or they may be located 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 xdt:untypedAny in the case of an element, and xdt: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 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 xdt:untypedAny in the case of an element, and xdt:untypedAtomic in the case of an attribute.

[ERR XT1510] 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. The processor must signal the error. As with other type errors, the error may be signaled statically if it can be detected statically.

[ERR XT1515] 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. The processor must signal the error. 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.

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 data type).

  • If the element or attribute is not considered valid, the transformation fails.

[ERR XT1520] It is a static error if the value of the type attribute of an xsl:element, xsl:attribute, xsl:copy, xsl:copy-of, 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 XT1530] It is a static error if the value of the type attribute of an xsl:attribute instruction refers to a complex type definition.

[ERR XT1540] 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.

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" is not 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 2.0 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 XPath 2.0 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]. 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 XPath data model by the mapping described in [Data Model] (Section 3.3.1 Mapping PSVI Additions to TypesDM). This process creates nodes with simple or complex type annotations based on the types established during schema validation.

19.2.2 Validating Document Nodes

It is possible to apply validation to a document node. The circumstances under which this happens are as follows:

  • A result tree is constructed implicitly in the absence of the xsl:result-document instruction, and the default-validation attribute of the xsl:stylesheet element in the principal stylesheet module requests validation.

  • A result tree is constructed using an xsl:result-document instruction, and the validation or type attribute is specified explicitly or implicitly.

  • The xsl:copy instruction is used when the context item is a document node, and the validation or type attribute is specified explicitly or implicitly.

  • One or more of the items selected by the xsl:copy-of instruction is a document node, and the validation or type attribute is specified explicitly or implicitly.

Validation is never applied to temporary trees, nor to document nodes created using xsl:message, even if the default-validation attribute of the containing xsl:stylesheet element requests validation. (This is equivalent to using validation="preserve": nodes within temporary trees retain their type annotation.)

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 xdt:untypedAny, while attributes have their type annotation set to xdt: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 XT1550] 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 19.2.1 Validating Constructed Elements and Attributes.

    Note:

    The type attribute on 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 2.0 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 XPath 2.0 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 XT1555] It is a type error if, when validating a document node, document-level constraints are not satisfied. These constraints include identity constraints (xs:unique, xs:key, and xs:keyref) and ID/IDREF constraints.

20 Serialization

A processor may output a result tree as a sequence of octets, although it is not required to be able to do so (see 21 Conformance). Stylesheet authors can use the xsl:output declaration to specify how they wish result trees to be serialized. If a processor serializes the result tree, it should do so as specified by these elements; however, it is not required to do so.

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 and xsl:character-map declarations.

<!-- Category: declaration -->
<xsl:output
  name? = qname
  method? = "xml" | "html" | "xhtml" | "text" | qname-but-not-ncname
  cdata-section-elements? = qnames
  doctype-public? = string
  doctype-system? = string
  encoding? = string
  escape-uri-attributes? = "yes" | "no"
  include-content-type? = "yes" | "no"
  indent? = "yes" | "no"
  media-type? = string
  normalize-unicode? = "yes" | "no"
  omit-xml-declaration? = "yes" | "no"
  standalone? = "yes" | "no"
  undeclare-namespaces? = "yes" | "no"
  use-character-maps? = qnames
  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 in a stylesheet 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.]

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 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 the cdata-section-elements attribute, 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 (space separated) of the 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.

[ERR XT1560] 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.

The values of attributes are defaulted after the xsl:output elements have been merged; different output methods may have different default values for an attribute.

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 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 result trees are both created (implicitly or explicitly) using relative URIs in the href attribute of the xsl:result-document instruction, then these relative URIs 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 result tree.

[ERR XT1570] The value must be a valid QName. If the QName does not have a prefix, then it identifies a method specified in [XSLT and XQuery Serialization] and must be one of xml, html, xhtml, or text. If the QName has a prefix, then the 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 is chosen as follows. If the document node of the 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 there are no xsl:output elements or if none of the xsl:output elements specifies a value for the method attribute.

The other attributes on xsl:output provide parameters for the output method. The following attributes are allowed:

20.1 Character Maps

[Definition: A character map allows a specific character appearing in a text or attribute node in the 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 = qname
  use-character-maps? = qnames>
  <!-- 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.

[ERR XT1580] 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 XT1590] It is a static error if a name in the use-character-maps attribute does not match the name attribute of any xsl:character-map in the stylesheet.

[ERR XT1600] 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 20.2 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 char="«" string="&lt;%"/>   
  <xsl:output-character char="»" string="%&gt;"/>
  <xsl:output-character char="§" 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 because the serialization specification requires 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>

20.2 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 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 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-output property set.

Example: Disable Output Escaping

For example,

<xsl:text disable-output-escaping="yes">&lt;</xsl:text>

should generate the single character <.

[ERR XT1610] It is a recoverable dynamic error for output escaping to be disabled for an xsl:value-of or xsl:text instruction that is used to generate something other than a text node in the result tree. Thus, it is an error to disable output escaping for an xsl:value-of or xsl:text element that is used to generate the string value of a comment, processing instruction or attribute node. The optional recovery action is to ignore disable-output-escaping attribute.

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:

&lt;title&gt;&lt;![CDATA[This is not ]]&gt;&lt;hr/&gt;&lt;![CDATA[ good coding practice]]&gt;&lt;/title&gt;

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 it does not perform any output escaping.

A processor will only be able to disable output escaping if it controls how the result tree is output. This might not always be the case. For example, the result tree might be used as the source tree for another XSLT transformation instead of being output. It is implementation-defined whether (and under what circumstances) disabling output escaping is supported.

[ERR XT1620] It is a recoverable dynamic error if an xsl:value-of or xsl:text instruction specifies that output escaping is to be disabled and the implementation does not support this. The optional recovery action is to ignore the disable-output-escaping attribute.

[ERR XT1630] It is a recoverable dynamic error if an xsl:value-of or xsl:text instruction specifies that output escaping is to be disabled when when writing to a result tree that is not being serialized. The optional recovery action is to ignore the disable-output-escaping attribute.

In particular, it is implementation-defined what happens when output escaping is disabled for a text node that is written to a temporary tree rather than a final result tree. The implementation may retain the information that output escaping was disabled, and use it when the relevant node is subsequently copied to a final result tree, but it is not required to do so. The fact that output escaping was disabled is not represented explicitly in the data model, and must not affect the result of any expressions that access the temporary tree.

[ERR XT1640] It is a recoverable dynamic error if output escaping is disabled for a character that is not representable in the encoding that the processor is using for output. The optional recovery action is to ignore the disable-output-escaping attribute.

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:

The facility to define character maps for use during serialization, as described in 20.1 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.

21 Conformance

A processor that claims conformance with this specification must claim conformance either as a basic XSLT processor or as a schema-aware XSLT processor. The rules for these two conformance levels are defined in the following sections.

A processor that claims conformance at either of these two levels may additionally claim conformance with either or both of the following optional features: the serialization feature, defined in 21.3 Serialization Feature, and the backwards compatibility feature, defined in 21.4 Backwards Compatibility Feature.

Note:

There is no conformance level or feature defined in this specification that requires implementation of the static typing features described in [XPath 2.0]. 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 2.0 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 one or more trees supplied as instances of the data model defined in [Data Model]. It is not required that the processor supports any particular method of constructing input data models, but conformance can only be tested if it provides a mechanism that enables data model instances representing the stylesheet and primary source document data model to be constructed and supplied as input to the processor.

The output of the XSLT processor consists of one or more trees. It is not required that the processor supports any particular method of accessing a result tree, but if it does not support the serialization module, 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 3.9 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, the action depends on whether the error is classified as a recoverable error. If a non-recoverable error occurs, 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.

21.1 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 certain explicitly-identified constructs related to schema processing.] These constructs are listed below.

The mandatory requirements of this specification are taken to include the mandatory requirements of XPath 2.0, as described in [XPath 2.0]. 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.

A basic XSLT processor must enforce the following restrictions. It must signal a static or dynamic error when the restriction is violated, as described below.

[ERR XT1650] A basic XSLT processor must signal a static error if the stylesheet includes an xsl:import-schema declaration.

Note:

Note that 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 3.12 Built-in Types.

[ERR XT1660] A basic XSLT processor must signal a static error if the stylesheet includes an [xsl:]type attribute, or an [xsl:]validation or default-validation attribute with a value other than strip.

A basic XSLT processor constrains the data model as follows:

  • Atomic values must belong to one of the following atomic types:

    xs:string
    xs:boolean
    xs:decimal
    xs:integer
    xs:double
    xs:date
    xs:time
    xs:dateTime
    xs:QName
    xs:anyURI
    xdt:untypedAtomic
    xdt:dayTimeDuration
    xdt:yearMonthDuration

    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 static context, which defines the full set of type names recognized by an XSLT processor and also by the XPath processor, includes the types listed, plus xs:anyType, xs:anySimpleType, xdt:untypedAny, and xdt:anyAtomicType.

    The set of constructor functions available are limited to those that construct values of the above types.

  • Element nodes must be annotated with the type annotation xdt:untypedAny, and attribute nodes with the type annotation xdt:untypedAtomic.

    Note:

    See however 4.4 Attributes Types and DTD Validation, which makes special provision for attributes defined in a DTD as being ID attributes.

[ERR XT1665] A basic XSLT processor must raise a non-recoverable dynamic error if the input to the processor includes a node with a type annotation other than xdt:untypedAny or xdt:untypedAtomic, or an atomic value of a type other than those which a basic XSLT processor supports.

Note:

Although this is expressed in terms of a requirement to detect invalid input, an alternative approach is for a basic XSLT 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 node, trees passed as stylesheet parameters, trees accessed using the document, doc FO, and collection FO functions, and trees returned by extension functions and extension instructions.

21.2 Schema-Aware XSLT Processor

[Definition: A schema-aware XSLT processor is an XSLT processor that implements all the mandatory requirements of this specification, including those features that a basic XSLT processor signals as an error. The mandatory requirements of this specification are taken to include the mandatory requirements of XPath 2.0, as described in [XPath 2.0]. 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.]

21.3 Serialization Feature

[Definition: A processor that claims conformance with the serialization feature must support the conversion of a result tree to a sequence of octets following the rules defined in 20 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, xsl:value-of, or xsl:attribute.

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; these declarations should be ignored.

21.4 Backwards Compatibility Feature

[Definition: A processor that claims conformance with the backwards compatibility feature must support the processing of stylesheet instructions and XPath expressions with backwards compatible behavior, as defined in 3.8 Backwards-Compatible Processing.]

[ERR XT1670] A processor that does not claim conformance with the backwards compatibility feature must raise a non-recoverable dynamic error if an instruction is evaluated containing an [xsl:]version attribute that invokes backwards compatible behavior.

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 or XSLT 2.0. 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 backwards 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.

A References

A.1 Normative References

Data Model
World Wide Web Consortium. XQuery 1.0 and XPath 2.0 Data Model W3C Working Draft. See http://www.w3.org/TR/xpath-datamodel/
Functions and Operators
World Wide Web Consortium. XQuery 1.0 and XPath 2.0 Functions and Operators. W3C Working Draft. See http://www.w3.org/TR/xpath-functions/
XML Information Set
World Wide Web Consortium. XML Information Set. W3C Recommendation. See http://www.w3.org/TR/xml-infoset/
ISO 3166-1
ISO (International Organization for Standardization) Codes for the representation of names of countries and their subdivisions - Part 1: Country codes ISO 3166-1:1997.
ISO 8601
ISO (International Organization for Standardization) Data elements and interchange formats - Information interchange - Representation of dates and times. ISO 8601:2000(E), Second edition, 2000-12-15.
XSLT and XQuery Serialization
World Wide Web Consortium. XSLT 2.0 and XQuery 1.0 Data Model Serialization. W3C Recommendation. See http://www.w3.org/TR/xslt-xquery-serialization/
XML 1.0
World Wide Web Consortium. Extensible Markup Language (XML) 1.0 (Second Edition) W3C Recommendation. See http://www.w3.org/TR/2000/REC-xml-20001006
XML 1.1
World Wide Web Consortium. Extensible Markup Language (XML) 1.1 W3C Candidate Recommendation. See http://www.w3.org/TR/xml11/
XMLBASE
World Wide Web Consortium. XML Base. W3C Recommendation. See http://www.w3.org/TR/xmlbase/
XML Namespaces 1.0
World Wide Web Consortium. Namespaces in XML. W3C Recommendation. See http://www.w3.org/TR/REC-xml-names/
XML Namespaces 1.1
World Wide Web Consortium. Namespaces in XML. W3C Recommendation. See http://www.w3.org/TR/xml-names11/
XML Schema
World Wide Web Consortium. XML Schema Part 1: Structures and and XML Schema Part 2: Data Types. W3C Recommendation. See http://www.w3.org/TR/xmlschema-1/ and http://www.w3.org/TR/xmlschema-2/
XPath 2.0
World Wide Web Consortium. XML Path Language Version 2.0 W3C Working Draft. See http://www.w3.org/TR/xpath20/

A.2 Other References

Calendrical Calculations
Edward M. Reingold and Nachum Dershowitz. Calendrical Calculations Millennium edition (2nd Edition). Cambridge University Press, ISBN 0 521 77752 6
DOM2
World Wide Web Consortium. Document Object Model (DOM) Level 2 Core Specification. W3C Recommendation. See 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.
RFC2376
E. Whitehead, M. Murata. XML Media Types. IETF RFC 2376. See http://www.ietf.org/rfc/rfc2376.txt.
RFC2396
T. Berners-Lee, R. Fielding, and L. Masinter. Uniform Resource Identifiers (URI): Generic Syntax. IETF RFC 2396. See http://www.ietf.org/rfc/rfc2396.txt.
RFC3023
M. Murata, S. St.Laurent, and D. Cohn. XML Media Types. IETF RFC 3023. See http://www.ietf.org/rfc/rfc3023.txt.
UNICODE TR10
Unicode Consortium. Unicode Technical Standard #10. Unicode Collation Algorithm. Unicode Technical Report. See http://www.unicode.org/unicode/reports/tr10/.
XInclude
World Wide Web Consortium. XML Inclusions (XInclude) W3C Recommendation. See http://www.w3.org/TR/xinclude/
XML Stylesheet
World Wide Web Consortium. Associating Style Sheets with XML documents. W3C Recommendation. See http://www.w3.org/TR/xml-stylesheet/
XPointer
World Wide Web Consortium. XPointer Framework. W3C Recommendation, 25 March 2003. See http://www.w3.org/TR/xptr-framework/
XSL
World Wide Web Consortium. Extensible Stylesheet Language (XSL). W3C Recommendation. See http://www.w3.org/TR/xsl/
XSLT 1.0
World Wide Web Consortium. XSL Transformations (XSLT) Version 1.0 W3C Recommendation. See http://www.w3.org/TR/xslt
XSLT 2.0 Requirements
World Wide Web Consortium. XSLT Requirements Version 2.0 W3C Working Draft. See http://www.w3.org/TR/xslt20req

B The XSLT Media Type

This appendix registers a new MIME media type, "application/xslt+xml".

B.1 Registration of MIME media type application/xslt+xml

MIME media type name:

application

MIME subtype name:

xslt+xml

Required parameters:

None.

Optional parameters:
charset

This parameter has identical semantics to the charset parameter of the application/xml media type as specified in [RFC3023].

Encoding considerations:

By virtue of XSLT content being XML, it has the same considerations when sent as "application/xslt+xml" as does XML. See RFC 3023, section 3.2.

Security considerations:

Several XSLT instructions may cause arbitrary URIs to be dereferenced. In this case, the security issues of RFC1738, section 6, should be considered.

In addition, because of the extensibility features for XSLT, it is possible that "application/xslt+xml" may describe content that has security implications beyond those described here. However, if the processor follows only the normative semantics of this specification, this content will be ignored. Only in the case where the processor recognizes and processes the additional content, or where further processing of that content is dispatched to other processors, would security issues potentially arise. And in that case, they would fall outside the domain of this registration document.

Interoperability considerations:

This specification describes processing semantics that dictate behavior that must be followed when dealing with, among other things, unrecognized elements.

Because XSLT is extensible, conformant "application/xslt+xml" processors can expect that content received is well-formed XML, but it cannot be guaranteed that the content is valid XSLT or that the processor will recognize all of the elements and attributes in the document.

Published specification:

This media type registration is for XSLT stylesheet modules as described by this specification.

Applications which use this media type:

Some authors have already started to write XSLT 2.0 documents. However that content is currently most often described using the unregistered media type "text/xslt".

There is no experimental, vendor specific, or personal tree predecessor to "application/xslt+xml", reflecting the fact that no applications currently recognize it. This new type is being registered in order to allow for the expected deployment of XSLT 2.0 on the World Wide Web, as a first class XML application.

Additional information:
Magic number(s):

There is no single initial octet sequence that is always present in XSLT documents.

File extension(s):

XSLT documents are most often identified with the extensions ".xsl" or ".xslt".

Macintosh File Type Code(s):

TEXT

Person & email address to contact for further information:

Norman Walsh, <Norman.Walsh@Sun.COM>.

Intended usage:

COMMON

Author/Change controller:

The XSLT specification is a work product of the World Wide Web Consortium's XSL Working Group. The W3C has change control over these specifications.

B.2 Fragment Identifiers

For documents labeled as "application/xslt+xml", the fragment identifier notation is exactly that for "application/xml", as specified in RFC 3023.

C Glossary (Non-Normative)

alias

A stylesheet can use the xsl