XSL Transformations (XSLT)
Version 1.0

W3C Recommendation 16 November 1999
incorporating errata through 2 November 2005

This version (with errata):: http://skew.org/xml/specs/xslt (unofficial)
This version (without errata):: http://www.w3.org/TR/1999/REC-xslt-19991116
(available in XML or HTML)
Latest version:: http://www.w3.org/TR/xslt
Previous versions:: http://www.w3.org/TR/1999/PR-xslt-19991008
http://www.w3.org/1999/08/WD-xslt-19990813
http://www.w3.org/1999/07/WD-xslt-19990709
http://www.w3.org/TR/1999/WD-xslt-19990421
http://www.w3.org/TR/1998/WD-xsl-19981216
http://www.w3.org/TR/1998/WD-xsl-19980818
Editor:: James Clark <jjc@jclark.com>

Abstract

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

XSLT is designed for use as part of XSL, which is a stylesheet language for XML. In addition to XSLT, XSL includes an XML vocabulary for specifying formatting. XSL specifies the styling of an XML document by using XSLT to describe how the document is transformed into another XML document that uses the formatting vocabulary.

XSLT is also designed to be used independently of XSL. However, XSLT is not intended as a completely general-purpose XML transformation language. Rather it is designed primarily for the kinds of transformations that are needed when XSLT is used as part of XSL.

Status of this document

This document has been reviewed by W3C Members and other interested parties and has been endorsed by the Director as a W3C Recommendation. It is a stable document and may be used as reference material or cited as a normative reference from other documents. W3C's role in making the Recommendation is to draw attention to the specification and to promote its widespread deployment. This enhances the functionality and interoperability of the Web.

The list of known errors in this specification is available at http://www.w3.org/1999/11/REC-xslt-19991116-errata.

Comments on this specification may be sent to xsl-editors@w3.org; archives of the comments are available. 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.

A list of current W3C Recommendations and other technical documents can be found at http://www.w3.org/TR.

This specification has been produced as part of the W3C Style activity.

1 Introduction
2 Stylesheet Structure
    2.1 XSLT Namespace
    2.2 Stylesheet Element
    2.3 Literal Result Element as Stylesheet
    2.4 Qualified Names
    2.5 Forwards-Compatible Processing
    2.6 Combining Stylesheets
        2.6.1 Stylesheet Inclusion
        2.6.2 Stylesheet Import
    2.7 Embedding Stylesheets
3 Data Model
    3.1 Root Node Children
    3.2 Base URI
    3.3 Unparsed Entities
    3.4 Whitespace Stripping
4 Expressions
5 Template Rules
    5.1 Processing Model
    5.2 Patterns
    5.3 Defining Template Rules
    5.4 Applying Template Rules
    5.5 Conflict Resolution for Template Rules
    5.6 Overriding Template Rules
    5.7 Modes
    5.8 Built-in Template Rules
6 Named Templates
7 Creating the Result Tree
    7.1 Creating Elements and Attributes
        7.1.1 Literal Result Elements
        7.1.2 Creating Elements with xsl:element
        7.1.3 Creating Attributes with xsl:attribute
        7.1.4 Named Attribute Sets
    7.2 Creating Text
    7.3 Creating Processing Instructions
    7.4 Creating Comments
    7.5 Copying
    7.6 Computing Generated Text
        7.6.1 Generating Text with xsl:value-of
        7.6.2 Attribute Value Templates
    7.7 Numbering
        7.7.1 Number to String Conversion Attributes
8 Repetition
9 Conditional Processing
    9.1 Conditional Processing with xsl:if
    9.2 Conditional Processing with xsl:choose
10 Sorting
11 Variables and Parameters
    11.1 Result Tree Fragments
    11.2 Values of Variables and Parameters
    11.3 Using Values of Variables and Parameters with xsl:copy-of
    11.4 Top-level Variables and Parameters
    11.5 Variables and Parameters within Templates
    11.6 Passing Parameters to Templates
12 Additional Functions
    12.1 Multiple Source Documents
    12.2 Keys
    12.3 Number Formatting
    12.4 Miscellaneous Additional Functions
13 Messages
14 Extensions
    14.1 Extension Elements
    14.2 Extension Functions
15 Fallback
16 Output
    16.1 XML Output Method
    16.2 HTML Output Method
    16.3 Text Output Method
    16.4 Disabling Output Escaping
17 Conformance
18 Notation

Appendices

A References
    A.1 Normative References
    A.2 Other References
B Element Syntax Summary
C DTD Fragment for XSLT Stylesheets (Non-Normative)
D Examples (Non-Normative)
    D.1 Document Example
    D.2 Data Example
E Acknowledgements (Non-Normative)
F Changes from Proposed Recommendation (Non-Normative)
G Features under Consideration for Future Versions of XSLT (Non-Normative)

1 Introduction

This specification defines the syntax and semantics of the XSLT language. A transformation in the XSLT language is expressed as a well-formed XML document [XML] conforming to the Namespaces in XML Recommendation [XML Names] or [XML Names 1.1], which may include both elements that are defined by XSLT and elements that are not defined by XSLT. For convenience, XML 1.0 and XML Names 1.0 references are usually used. Thus, URI references are also used though IRI may also be supported. In some cases, the XML 1.0 and XML 1.1 definitions may be exactly the same. XSLT-defined elements are distinguished by belonging to a specific XML namespace (see [2.1 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.

A transformation expressed in XSLT describes rules for transforming a source tree into a result tree. The transformation is achieved by associating patterns with templates. A pattern is matched against elements in the source tree. A template is instantiated to create part of the result tree. The result tree is separate from the source tree. The structure of the result tree can be completely different from the structure of the source tree. In constructing the result tree, elements from the source tree can be filtered and reordered, and arbitrary structure can be added.

A transformation expressed in XSLT is called a stylesheet. This is because, in the case when XSLT is transforming into the XSL formatting vocabulary, the transformation functions as a stylesheet.

This document does not specify how an XSLT stylesheet is associated with an XML document. It is recommended that XSL processors support the mechanism described in [XML Stylesheet]. When this or any other mechanism yields a sequence of more than one XSLT stylesheet to be applied simultaneously to a XML document, then the effect should be the same as applying a single stylesheet that imports each member of the sequence in order (see [2.6.2 Stylesheet Import]).

A stylesheet contains a set of template rules. A template rule has two parts: a pattern which is matched against nodes in the source tree and a template which can be instantiated to form part of the result tree. This allows a stylesheet to be applicable to a wide class of documents that have similar source tree structures.

A template is instantiated for a particular source element to create part of the result tree. A template can contain elements that specify literal result element structure. A template can also contain elements from the XSLT namespace that are instructions for creating result tree fragments. When a template is instantiated, each instruction is executed and replaced by the result tree fragment that it creates. Instructions can select and process descendant source elements. Processing a descendant element creates a result tree fragment by finding the applicable template rule and instantiating its template. Note that elements are only processed when they have been selected by the execution of an instruction. The result tree is constructed by finding the template rule for the root node and instantiating its template.

In the process of finding the applicable template rule, more than one template rule may have a pattern that matches a given element. However, only one template rule will be applied. The method for deciding which template rule to apply is described in [5.5 Conflict Resolution for Template Rules].

A single template by itself has considerable power: it can create structures of arbitrary complexity; it can pull string values out of arbitrary locations in the source tree; it can generate structures that are repeated according to the occurrence of elements in the source tree. For simple transformations where the structure of the result tree is independent of the structure of the source tree, a stylesheet can often consist of only a single template, which functions as a template for the complete result tree. Transformations on XML documents that represent data are often of this kind (see [D.2 Data Example]). XSLT allows a simplified syntax for such stylesheets (see [2.3 Literal Result Element as Stylesheet]).

When a template is instantiated, it is always instantiated with respect to a current node and a current node list. The current node is always a member of the current node list. Many operations in XSLT are relative to the current node. Only a few instructions change the current node list or the current node (see [5 Template Rules] and [8 Repetition]); during the instantiation of one of these instructions, the current node list changes to a new list of nodes and each member of this new list becomes the current node in turn; after the instantiation of the instruction is complete, the current node and current node list revert to what they were before the instruction was instantiated.

XSLT makes use of the expression language defined by [XPath] for selecting elements for processing, for conditional processing and for generating text.

XSLT provides two "hooks" for extending the language, one hook for extending the set of instruction elements used in templates and one hook for extending the set of functions used in XPath expressions. These hooks are both based on XML namespaces. This version of XSLT does not define a mechanism for implementing the hooks. See [14 Extensions].

NOTE: The XSL WG intends to define such a mechanism in a future version of this specification or in a separate specification.

The element syntax summary notation used to describe the syntax of XSLT-defined elements is described in [18 Notation].

The MIME media types text/xml and application/xml [RFC2376] should be used for XSLT stylesheets. It is possible that a media type will be registered specifically for XSLT stylesheets; if and when it is, that media type may also be used.

2 Stylesheet Structure

2.1 XSLT Namespace

The XSLT namespace has the URI http://www.w3.org/1999/XSL/Transform.

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 [2.2 Stylesheet Element] and [2.3 Literal Result Element as Stylesheet]).

XSLT processors must use the XML namespaces mechanism [XML Names] 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 [B Element Syntax Summary]. Vendors 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 element mechanism specified in [14.1 Extension Elements].

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.

An element from the XSLT namespace may have any attribute not from the XSLT namespace, provided that the expanded-name of the attribute has a non-null namespace URI. The presence of such attributes must not change the behavior of XSLT elements and functions defined in this document. Thus, an XSLT processor is always free to ignore such attributes, and must ignore such attributes without giving an error if it does not recognize the namespace URI. Such attributes can provide, for example, unique identifiers, optimization hints, or documentation.

It is an error for an element from the XSLT namespace to have attributes with expanded-names that have null namespace URIs (i.e. attributes with unprefixed names) other than attributes defined for the element in this document.

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.

2.2 Stylesheet Element

<xsl:stylesheet id = id extension-element-prefixes = tokens exclude-result-prefixes = tokens version = number>  </xsl:stylesheet>

<xsl:transform id = id extension-element-prefixes = tokens exclude-result-prefixes = tokens version = number>  </xsl:transform>

A stylesheet is represented by an xsl:stylesheet element in an XML document. xsl:transform is allowed as a synonym for xsl:stylesheet.

An xsl:stylesheet element must have a version attribute, indicating the version of XSLT that the stylesheet requires. For this version of XSLT, the value should be 1.0. When the value is not equal to 1.0, forwards-compatible processing mode is enabled (see [2.5 Forwards-Compatible Processing]).

The xsl:stylesheet element may contain the following types of elements:

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

An element occurring as a child of an xsl:stylesheet element is called a top-level element.

This example shows the structure of a stylesheet. Ellipses (...) indicate where attribute values or content have been omitted. Although this example shows one of each type of allowed element, stylesheets may contain zero or more of each of these elements.

<xsl:stylesheet version="1.0"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:import href="..."/>

  <xsl:include href="..."/>

  <xsl:strip-space elements="..."/>
  
  <xsl:preserve-space elements="..."/>

  <xsl:output method="..."/>

  <xsl:key name="..." match="..." use="..."/>

  <xsl:decimal-format name="..."/>

  <xsl:namespace-alias stylesheet-prefix="..." result-prefix="..."/>

  <xsl:attribute-set name="...">
    ...
  </xsl:attribute-set>

  <xsl:variable name="...">...</xsl:variable>

  <xsl:param name="...">...</xsl:param>

  <xsl:template match="...">
    ...
  </xsl:template>

  <xsl:template name="...">
    ...
  </xsl:template>

</xsl:stylesheet>

The order in which the children of the xsl:stylesheet element occur is not significant except for xsl:import elements and for error recovery. Users are free to order the elements as they prefer, and stylesheet creation tools need not provide control over the order in which the elements occur.

In addition, the xsl:stylesheet element may contain any element not from the XSLT namespace, provided that the expanded-name of the element has a non-null namespace URI. The presence of such top-level elements must not change the behavior of XSLT elements and functions defined in this document; for example, it would not be permitted for such a top-level element to specify that xsl:apply-templates was to use different rules to resolve conflicts. Thus, an XSLT processor is always free to ignore such top-level elements, and must ignore a top-level element without giving an error if it does not recognize the namespace URI. Such elements can provide, for example,

information used by extension elements or extension functions (see [14 Extensions]),
information about what to do with the result tree,
information about how to obtain the source tree,
metadata about the stylesheet,
structured documentation for the stylesheet.

2.3 Literal Result Element as Stylesheet

A simplified syntax is allowed for stylesheets that consist of only a single template for the root node. The stylesheet may consist of just a literal result element (see [7.1.1 Literal Result Elements]). Such a stylesheet is equivalent to a stylesheet with an xsl:stylesheet element containing a template rule containing the literal result element; the template rule has a match pattern of /. For example

<html xsl:version="1.0"
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
      xmlns="http://www.w3.org/TR/xhtml1/strict">
  <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="1.0"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                xmlns="http://www.w3.org/TR/xhtml1/strict">
<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>

A literal result element that is the document element of a stylesheet must have an xsl:version attribute, which indicates the version of XSLT that the stylesheet requires. For this version of XSLT, the value should be 1.0; the value must be a Number. Other literal result elements may also have an xsl:version attribute. When the xsl:version attribute is not equal to 1.0, forwards-compatible processing mode is enabled (see [2.5 Forwards-Compatible Processing]).

The allowed content of a literal result element when used as a stylesheet is no different from when it occurs within a stylesheet. Thus, a literal result element used as a stylesheet cannot contain top-level elements.

In some situations, the only way that a system can recognize that an XML document needs to be processed by an XSLT processor as an XSLT stylesheet is by examining the XML document itself. Using the simplified syntax makes this harder.

NOTE: For example, another XML language (AXL) might also use an axl:version on the document element to indicate that an XML document was an AXL document that required processing by an AXL processor; if a document had both an axl:version attribute and an xsl:version attribute, it would be unclear whether the document should be processed by an XSLT processor or an AXL processor.

Therefore, the simplified syntax should not be used for XSLT stylesheets that may be used in such a situation. This situation can, for example, arise when an XSLT stylesheet is transmitted as a message with a MIME media type of text/xml or application/xml to a recipient that will use the MIME media type to determine how the message is processed.

2.4 Qualified Names

The name of an internal XSLT object, specifically a named template (see [6 Named Templates]), a mode (see [5.7 Modes]), an attribute set (see [7.1.4 Named Attribute Sets]), a key (see [12.2 Keys]), a decimal-format (see [12.3 Number Formatting]), a variable or a parameter (see [11 Variables and Parameters]) is specified as a QName. If it has a prefix, then the prefix is expanded into a URI reference using the namespace declarations in effect on the attribute in which the name occurs. The expanded-name 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 is not used for unprefixed names.

2.5 Forwards-Compatible Processing

An element enables forwards-compatible mode for itself, its attributes, its descendants and their attributes if either it is an xsl:stylesheet element whose version attribute is not equal to 1.0, or it is a literal result element that has an xsl:version attribute whose value is not equal to 1.0. A literal result element that has an xsl:version attribute whose value is equal to 1.0 disables forwards-compatible mode for itself, its attributes, its descendants and their attributes.

If an element is processed in forwards-compatible mode, then:

if it is a top-level element and XSLT 1.0 does not allow such elements as top-level elements, then the element must be ignored along with its content;
if it is an element in a template and XSLT 1.0 does not allow such elements to occur in templates, then if the element is not instantiated, an error must not be signaled, and if the element is instantiated, the XSLT must perform fallback for the element as specified in [15 Fallback];
if the element has an attribute that XSLT 1.0 does not allow the element to have or if the element has an optional attribute with a value that the XSLT 1.0 does not allow the attribute to have, then the attribute must be ignored.

Thus, any XSLT 1.0 processor must be able to 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="1.1"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:template match="/">
    <xsl:choose>
      <xsl:when test="system-property('xsl:version') >= 1.1">
        <xsl:exciting-new-1.1-feature/>
      </xsl:when>
      <xsl:otherwise>
        <html>
        <head>
          <title>XSLT 1.1 required</title>
        </head>
        <body>
          <p>Sorry, this stylesheet requires XSLT 1.1.</p>
        </body>
        </html>
      </xsl:otherwise>
    </xsl:choose>
  </xsl:template>
</xsl:stylesheet>

NOTE: If a stylesheet depends crucially on a top-level element introduced by a version of XSLT after 1.0, then the stylesheet can use an xsl:message element with terminate="yes" (see [13 Messages]) to ensure that XSLT processors implementing earlier versions of XSLT will not silently ignore the top-level element. For example,
<xsl:stylesheet version="1.5"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

  <xsl:important-new-1.1-declaration/>

  <xsl:template match="/">
    <xsl:choose>
      <xsl:when test="system-property('xsl:version') &lt; 1.1">
        <xsl:message terminate="yes">
          <xsl:text>Sorry, this stylesheet requires XSLT 1.1.</xsl:text>
        </xsl:message>
      </xsl:when>
      <xsl:otherwise>
        ...
      </xsl:otherwise>
    </xsl:choose>
  </xsl:template>
  ...
</xsl:stylesheet>

If an expression occurs in an attribute that is processed in forwards-compatible mode, then an XSLT processor must recover from errors in the expression as follows:

if the expression does not match the syntax allowed by the XPath grammar, then an error must not be signaled unless the expression is actually evaluated;
if the expression calls a function with an unprefixed name that is not part of the XSLT library, then an error must not be signaled unless the function is actually called;
if the expression calls a function with a number of arguments that XSLT does not allow or with arguments of types that XSLT does not allow, then an error must not be signaled unless the function is actually called.

2.6 Combining Stylesheets

XSLT provides two mechanisms to combine stylesheets:

an inclusion mechanism that allows stylesheets to be combined without changing the semantics of the stylesheets being combined, and
an import mechanism that allows stylesheets to override each other.

2.6.1 Stylesheet Inclusion

 <xsl:include href = uri-reference />

An XSLT stylesheet may include another XSLT stylesheet using an xsl:include element. The xsl:include element has an href attribute whose value is a URI reference identifying the stylesheet to be included. A relative URI is resolved relative to the base URI of the xsl:include element (see [3.2 Base URI]).

The xsl:include element is only allowed as a top-level element.

The inclusion works at the XML tree level. The resource located by the href attribute value is parsed as an XML document, and the children of the xsl:stylesheet element in this document replace the xsl:include element in the including document. The fact that template rules or definitions are included does not affect the way they are processed.

The included stylesheet may use the simplified syntax described in [2.3 Literal Result Element as Stylesheet]. The included stylesheet is treated the same as the equivalent xsl:stylesheet element.

It is an error if a stylesheet directly or indirectly includes itself.

NOTE: Including a stylesheet multiple times 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'.

2.6.2 Stylesheet Import

<xsl:import href = uri-reference />

An XSLT stylesheet may import another XSLT stylesheet using an xsl:import element. Importing a stylesheet is the same as including it (see [2.6.1 Stylesheet Inclusion]) except that definitions and template rules in the importing stylesheet take precedence over template rules and definitions in the imported stylesheet; this is described in more detail below. The xsl:import element has an href attribute whose value is a URI reference identifying the stylesheet to be imported. A relative URI is resolved relative to the base URI of the xsl:import element (see [3.2 Base URI]).

The xsl:import element is only allowed as a top-level element. The xsl:import element children must precede all other element children of an xsl:stylesheet element, including any xsl:include element children. When xsl:include is used to include a stylesheet, any xsl:import elements in the included document are moved up in the including document to after any existing xsl:import elements in the including document.

For example,

<xsl:stylesheet version="1.0"
                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>

The xsl:stylesheet elements encountered during processing of a stylesheet that contains xsl:import elements are treated as forming an import tree. In the import tree, each xsl:stylesheet element has one import child for each xsl:import element that it contains. Any xsl:include elements are resolved before constructing the import tree. An xsl:stylesheet element in the import tree is defined to have lower import precedence than another xsl:stylesheet element in the import tree if it would be visited before that xsl:stylesheet element in a post-order traversal of the import tree (i.e. a traversal of the import tree in which an xsl:stylesheet element is visited after its import children). Each definition and template rule has import precedence determined by the xsl:stylesheet element that contains it.

For example, suppose

stylesheet A imports stylesheets B and C in that order;
stylesheet B imports stylesheet D;
stylesheet C imports stylesheet E.

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

NOTE: Since xsl:import elements are required to occur before any definitions or template rules, an implementation that processes imported stylesheets at the point at which it encounters the xsl:import element will encounter definitions and template rules in increasing order of import precedence.

In general, a definition or template rule with higher import precedence takes precedence over a definition or template rule with lower import precedence. This is defined in detail for each kind of definition and for template rules.

It is an error if a stylesheet directly or indirectly imports itself. Apart from this, the case where a stylesheet with a particular URI is imported in multiple places is not treated specially. The import tree will have a separate xsl:stylesheet for each place that it is imported.

NOTE: If xsl:apply-imports is used (see [5.6 Overriding Template Rules]), the behavior may be different from the behavior if the stylesheet had been imported only at the place with the highest import precedence.

2.7 Embedding Stylesheets

Normally an XSLT stylesheet is a complete XML document with the xsl:stylesheet element as the document element. However, an XSLT stylesheet 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 is allowed to have an ID attribute that specifies a unique identifier.

NOTE: In order for such an attribute to be used with the XPath id function, it must actually be declared in the DTD as being an ID.

The following example shows how the xml-stylesheet processing instruction [XML Stylesheet] can be used to allow a 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="text/xml" href="#style1"?>
<!DOCTYPE doc SYSTEM "doc.dtd">
<doc>
<head>
<xsl:stylesheet id="style1"
                version="1.0"
                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 that is embedded in the document to which it is to be applied or that may be included or imported into a stylesheet that is so embedded typically needs to contain a template rule that specifies that xsl:stylesheet elements are to be ignored.

3 Data Model

The data model used by XSLT is the same as that used by XPath with the additions described in this section. XSLT operates on source, result and stylesheet documents using the same data model. Any two XML documents that have the same tree will be treated the same by XSLT.

Processing instructions and comments in the stylesheet are ignored: the stylesheet is treated as if neither processing instruction nodes nor comment nodes were included in the tree that represents the stylesheet.

3.1 Root Node Children

The normal restrictions on the children of the root node are relaxed for the result tree. The result tree may have any sequence of nodes as children that would be possible for an element node. In particular, it may have text node children, and any number of element node children. When written out using the XML output method (see [16 Output]), it is possible that a result tree will not be a well-formed XML document; however, it will always be a well-formed external general parsed entity.

When the source tree is created by parsing a well-formed XML document, the root node of the source tree will automatically satisfy the normal restrictions of having no text node children and exactly one element child. When the source tree is created in some other way, for example by using the DOM, the usual restrictions are relaxed for the source tree as for the result tree.

3.2 Base URI

Every node also has an associated URI called its base URI, which is used for resolving attribute values that represent relative URIs into absolute URIs. If an element or processing instruction occurs in an external entity, the base URI of that element or processing instruction is the URI of the external entity; otherwise, the base URI is the base URI of the document. The base URI of the document node is the URI of the document entity. The base URI for a text node, a comment node, an attribute node or a namespace node is the base URI of the parent of the node.

3.3 Unparsed Entities

The root node has a mapping that gives the URI for each unparsed entity declared in the document's DTD. The URI is generated from the system identifier and public identifier specified in the entity declaration. The XSLT processor may use the public identifier to generate a URI for the entity instead of the URI specified in the system identifier. If the XSLT processor does not use the public identifier to generate the URI, it must use the system identifier; if the system identifier is a relative URI, it must be resolved into an absolute URI using the URI of the resource containing the entity declaration as the base URI [RFC2396].

3.4 Whitespace Stripping

After the tree for a source document or stylesheet document has been constructed, but before it is otherwise processed by XSLT, some text nodes are stripped. A text node is never stripped unless it contains only whitespace characters. Stripping the text node removes the text node from the tree. The stripping process takes as input a set of element names for which whitespace must be preserved. The stripping process is applied to both stylesheets and source documents, but the set of whitespace-preserving element names is determined differently for stylesheets and for source documents.

A text node is preserved if any of the following apply:

The element name of the parent of the text node is in the set of whitespace-preserving element names.
The text node contains at least one non-whitespace character. As in XML, a whitespace character is #x20, #x9, #xD or #xA.
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 text node is stripped.

The xml:space attributes are not stripped 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.

For stylesheets, the set of whitespace-preserving element names consists of just xsl:text.

 <xsl:strip-space elements = tokens />

 <xsl:preserve-space elements = tokens />

For source documents, the set of whitespace-preserving element names is specified by xsl:strip-space and xsl:preserve-space top-level elements. Whether an element name is included in the set of whitespace-preserving names is determined by the best match amongst xsl:strip-space or xsl:preserve-space elements: 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; an element name matches an xsl:strip-space or xsl:preserve-space element if it matches one of the NameTests. An element matches a NameTest if and only if the NameTest 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. This is determined in the same way as with template rules:

First, any match with lower import precedence than another match is ignored.
Next, any match that has a lower default priority than the default priority of another match is ignored.

It is an error if this leaves more than one match. An XSLT processor may signal the error; if it does not signal the error, it must recover by choosing, from amongst the matches that are left, the one that occurs last in the stylesheet.

3.5

The data model is capable of representing either an XML 1.0 document (conforming to [XML] and [XML Names]) or an XML 1.1 document (conforming to [XML 1.1] and [XML Names 1.1]), and it makes no distinction between the two. In principle, therefore, XSLT 1.0 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 1.0 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 defines capability to output XML 1.0 or XML 1.1 documents (16 Output). There is again no formal requirement on an XSLT processor to support either or both of these XML versions.

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.

4 Expressions

XSLT uses the expression language defined by XPath [XPath]. 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.

An expression must match the XPath production Expr.

Expressions occur as the value of certain attributes on XSLT-defined elements and within curly braces in attribute value templates.

In XSLT, an outermost expression (i.e. an expression that is not part of another expression) gets its context as follows:

the context node comes from the current node
the context position comes from the position of the current node in the current node list; the first position is 1
the context size comes from the size of the current node list
the variable bindings are the bindings in scope on the element which has the attribute in which the expression occurs (see [11 Variables and Parameters])
the set of namespace declarations are those in scope on the element which has the attribute in which the expression occurs; this includes the implicit declaration of the prefix xml required by the the XML Namespaces Recommendation [XML Names]; the default namespace (as declared by xmlns) is not part of this set
the function library consists of the core function library together with the additional functions defined in [12 Additional Functions] and extension functions as described in [14 Extensions]; it is an error for an expression to include a call to any other function

5 Template Rules

5.1 Processing Model

A list of source nodes is processed to create a result tree fragment. The result tree is constructed by processing a list containing just the root node. A list of source nodes is processed by appending the result tree structure created by processing each of the members of the list in order. A node is processed by finding all the template rules with patterns that match the node, and choosing the best amongst them; the chosen rule's template is then instantiated with the node as the current node and with the list of source nodes as the current node list. A template typically contains instructions that select an additional list of source nodes for processing. The process of matching, instantiation and selection is continued recursively until no new source nodes are selected for processing.

Implementations are free to process the source document in any way that produces the same result as if it were processed using this processing model.

5.2 Patterns

Template rules identify the nodes to which they apply by using a pattern. As well as being used in template rules, patterns are used for numbering (see [7.7 Numbering]) and for declaring keys (see [12.2 Keys]). 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. In particular, location paths that meet certain restrictions can be used as patterns. An expression that is also a pattern always evaluates to an object of type node-set. A node matches a pattern if the node is a member of the result of evaluating the pattern as an expression with respect to some possible context; the possible contexts are those whose context node is the node being matched or one of its ancestors.

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/item matches any item element with an olist parent
appendix//para matches any para element with an appendix ancestor element
/ matches the root node
text() matches any text node
processing-instruction() matches any processing instruction
node() matches any node other than an attribute node and the root node
id("W11") matches the element with unique ID W11
para[1] matches any para element that is the first para child element of its parent
*[position()=1 and self::para] matches any para element that is the first child element of its parent
para[last()=1] matches any para element that is the only para child element of its parent
items/item[position()>1] matches any item element that has an items parent and that is not the first item child of its parent
item[position() mod 2 = 1] would be true for any item element that is an odd-numbered item 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

A pattern must match the grammar for Pattern. A Pattern is a set of location path patterns separated by |. A location path pattern is a location path whose steps all use only the child or attribute axes. Although patterns must not use the descendant-or-self axis, patterns may use the // operator as well as the / operator. Location path patterns can also start with an id or key function call with a literal argument. Predicates in a pattern can use arbitrary expressions just like predicates in a location path.

Patterns

[1]	Pattern	::=	LocationPathPattern
			\| Pattern '\|' LocationPathPattern
[2]	LocationPathPattern	::=	'/' RelativePathPattern?
			\| IdKeyPattern (('/' \| '//') RelativePathPattern)?
			\| '//'? RelativePathPattern
[3]	IdKeyPattern	::=	'id' '(' Literal ')'
			\| 'key' '(' Literal ',' Literal ')'
[4]	RelativePathPattern	::=	StepPattern
			\| RelativePathPattern '/' StepPattern
			\| RelativePathPattern '//' StepPattern
[5]	StepPattern	::=	ChildOrAttributeAxisSpecifier NodeTest Predicate*
[6]	ChildOrAttributeAxisSpecifier	::=	AbbreviatedAxisSpecifier
			\| ('child' \| 'attribute') '::'

A pattern is defined to match a node if and only if there is possible context such that when the pattern is evaluated as an expression with that context, the node is a member of the resulting node-set. When a node is being matched, the possible contexts have a context node that is the node being matched or any ancestor of that node, and a context node list containing just the context node.

For example, p matches any p element, because for any p if the expression p is evaluated with the parent of the p element as context the resulting node-set will contain that p element as one of its members.

NOTE: This matches even a p element that is the document element, since the document root is the parent of the document element.

Although the semantics of patterns are specified indirectly in terms of expression evaluation, it is easy to understand the meaning of a pattern directly without thinking in terms of expression evaluation. In a pattern, | indicates alternatives; a pattern with one or more | separated alternatives matches if any one of the alternative matches. A pattern that consists of a sequence of StepPatterns separated by / or // is matched from right to left. The pattern only matches if the rightmost StepPattern matches and a suitable element matches the rest of the pattern; if the separator is / then only the parent is a suitable element; if the separator is //, then any ancestor is a suitable element. A StepPattern that uses the child axis matches if the NodeTest is true for the node and the node is not an attribute node. A StepPattern that uses the attribute axis matches if the NodeTest is true for the node and the node is an attribute node. When [] is present, then the first PredicateExpr in a StepPattern is evaluated with the node being matched as the context node and the siblings of the context node that match the NodeTest as the context node list, unless the node being matched is an attribute node, in which case the context node list is all the attributes that have the same parent as the attribute being matched and that match the NameTest.

For example

appendix//ulist/item[position()=1]

matches a node if and only if all of the following are true:

the NodeTest item is true for the node and the node is not an attribute; in other words the node is an item element
evaluating the PredicateExpr position()=1 with the node as context node and the siblings of the node that are item elements as the context node list yields true
the node has a parent that matches appendix//ulist; this will be true if the parent is a ulist element that has an appendix ancestor element.

5.3 Defining Template Rules

 <xsl:template match = pattern name = qname priority = number mode = qname>  </xsl:template>

A template rule is specified with the xsl:template element. The match attribute is a Pattern that identifies the source node or nodes to which the rule applies. The match attribute is required unless the xsl:template element has a name attribute (see [6 Named Templates]). It is an error for the value of the match attribute to contain a VariableReference. The content of the xsl:template element is the template that is instantiated when the template rule is applied.

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:inline-sequence formatting object with a font-weight property of bold.

<xsl:template match="emph">
  <fo:inline-sequence font-weight="bold">
    <xsl:apply-templates/>
  </fo:inline-sequence>
</xsl:template>

NOTE: Examples in this document use the fo: prefix for the namespace http://www.w3.org/1999/XSL/Format, which is the namespace of the formatting objects defined in [XSL].

As described next, the xsl:apply-templates element recursively processes the children of the source element.

5.4 Applying Template Rules

 <xsl:apply-templates select = node-set-expression mode = qname>  </xsl:apply-templates>

This example creates a block for a chapter element and then processes its immediate children.

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

In the absence of a select attribute, the xsl:apply-templates instruction processes all of the children of the current node, including text nodes. However, text nodes that have been stripped as specified in [3.4 Whitespace Stripping] will not be processed. If stripping of whitespace 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 function.

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 node-set. The selected set of nodes is processed in document order, unless a sorting specification is present (see [10 Sorting]). The following example processes all of the author children of the author-group:

<xsl:template match="author-group">
  <fo:inline-sequence>
    <xsl:apply-templates select="author"/>
  </fo:inline-sequence>
</xsl:template>

The following example processes all of the given-names of the authors that are children of author-group:

<xsl:template match="author-group">
  <fo:inline-sequence>
    <xsl:apply-templates select="author/given-name"/>
  </fo:inline-sequence>
</xsl:template>

This example processes all of the heading descendant elements of the book element.

<xsl:template match="book">
  <fo:block>
    <xsl:apply-templates select=".//heading"/>
  </fo:block>
</xsl:template>

It is also possible to process elements that are not descendants of the current 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>

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>

NOTE: 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.

NOTE: Typically, xsl:apply-templates is used to process only nodes that are descendants of the current 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 current 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.

5.5 Conflict Resolution for Template Rules

It is possible for a source node to match more than one template rule. The template rule to be used is determined as follows:

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.
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. The value of this must be a real number (positive or negative), matching the production Number with an optional leading minus sign (-). The default priority is computed as follows:
- If the pattern contains multiple alternatives separated by |, then it is treated equivalently to a set of template rules, one for each alternative.
- If the pattern has the form of a QName preceded by a ChildOrAttributeAxisSpecifier or has the form processing-instruction(Literal) preceded by a ChildOrAttributeAxisSpecifier, then the priority is 0.
- If the pattern has the form NCName:* preceded by a ChildOrAttributeAxisSpecifier, then the priority is -0.25.
- Otherwise, if the pattern consists of just a NodeTest preceded by a ChildOrAttributeAxisSpecifier, then the priority is -0.5.
- Otherwise, the priority is 0.5.
Thus, the most common kind of pattern (a pattern that tests for a node with a particular type and a particular expanded-name) has priority 0. The next less specific kind of pattern (a pattern that tests for a node with a particular type and an expanded-name with a particular namespace URI) has priority -0.25. Patterns less specific than this (patterns that just tests for nodes with particular types) have priority -0.5. Patterns more specific than the most common kind of pattern have priority 0.5.

It is an error if this leaves more than one matching template rule. An XSLT processor may signal the error; if it does not signal the error, it must recover by choosing, from amongst the matching template rules that are left, the one that occurs last in the stylesheet.

5.6 Overriding Template Rules

 <xsl:apply-imports />

A template rule that is being used to override a template rule in an imported stylesheet (see [5.5 Conflict Resolution for Template Rules]) can use the xsl:apply-imports element to invoke the overridden template rule.

At any point in the processing of a stylesheet, there is a current template rule. Whenever a template rule is chosen by matching a pattern, the template rule becomes the current template rule for the instantiation of the rule's template. When an xsl:for-each element is instantiated, the current template rule becomes null for the instantiation of the content of the xsl:for-each element.

xsl:apply-imports processes the current node using only template rules that were imported into the stylesheet element containing the current template rule; the node is processed in the current template rule's mode. It is an error if xsl:apply-imports is instantiated when the current template rule is null.

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>

5.7 Modes

Modes allow an element to be processed multiple times, each time producing a different result.

Both xsl:template and xsl:apply-templates have an optional mode attribute. The value of the mode attribute is a QName, which is expanded as described in [2.4 Qualified Names]. If xsl:template does not have a match attribute, it must not have a mode attribute. If an xsl:apply-templates element has a mode attribute, then it applies only to those template rules from xsl:template elements that have a mode attribute with the same value; if an xsl:apply-templates element does not have a mode attribute, then it applies only to those template rules from xsl:template elements that do not have a mode attribute.

5.8 Built-in Template Rules

There is a built-in template rule to allow recursive processing to continue in the absence of a successful pattern match by an explicit template rule in the stylesheet. This template rule applies to both element nodes and the root node. The following shows the equivalent of the built-in template rule:

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

There is also a built-in template rule for each mode, which allows recursive processing to continue in the same mode in the absence of a successful pattern match by an explicit template rule in the stylesheet. This template rule applies to both element nodes and the root node. The following shows the equivalent of the built-in template rule for mode m.

<xsl:template match="*|/" mode="m">
  <xsl:apply-templates mode="m"/>
</xsl:template>

There is also a built-in template rule for text and attribute nodes that copies text through:

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

The built-in template rule for processing instructions and comments is to do nothing.

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

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 the only template rule that is applied for namespace nodes.

The built-in template rules are treated as if they were imported implicitly before the stylesheet and so have lower import precedence than all other template rules. Thus, the author can override a built-in template rule by including an explicit template rule.

6 Named Templates

 <xsl:call-template name = qname>  </xsl:call-template>

Templates can be invoked by name. An xsl:template element with a name attribute specifies a named template. The value of the name attribute is a QName, which is expanded as described in [2.4 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 element invokes a template by name; it has a required name attribute that identifies the template to be invoked. Unlike xsl:apply-templates, xsl:call-template does not change the current node or the current node list.

The match, mode and priority attributes on an xsl:template element do not affect whether the template is invoked by an xsl:call-template element. Similarly, the name attribute on an xsl:template element does not affect whether the template is invoked by an xsl:apply-templates element.

It is an error if a stylesheet contains more than one template with the same name and same import precedence.

7 Creating the Result Tree

This section describes instructions that directly create nodes in the result tree.

7.1 Creating Elements and Attributes

7.1.1 Literal Result Elements

In a template, an element in the stylesheet that does not belong to the XSLT namespace and that is not an extension element (see [14.1 Extension Elements]) is instantiated to create an element node with the same expanded-name. The content of the element is a template, which is instantiated to give the content of the created element node. The created element node will have the attribute nodes that were present on the element node in the stylesheet tree, other than attributes with names in the XSLT namespace.

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 the XSLT namespace URI (http://www.w3.org/1999/XSL/Transform), a namespace URI declared as an extension namespace (see [14.1 Extension Elements]), or a namespace URI designated as an excluded namespace. A namespace URI is designated as an excluded namespace by using an exclude-result-prefixes attribute on an xsl:stylesheet element or an xsl:exclude-result-prefixes attribute on a literal result element. The value of both these attributes is a whitespace-separated list of namespace prefixes. The namespace bound to each of the prefixes is designated as an excluded namespace. It is an error if there is no namespace bound to the prefix on the element bearing the exclude-result-prefixes or 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 designation of a namespace as an excluded namespace is effective within the subtree of the stylesheet rooted at the element bearing the exclude-result-prefixes or xsl:exclude-result-prefixes attribute; a subtree rooted at an xsl:stylesheet element does not include any stylesheets imported or included by children of that xsl:stylesheet element.

NOTE: When a stylesheet uses a namespace declaration only for the purposes of addressing the source tree, specifying the prefix in the exclude-result-prefixes attribute will avoid superfluous namespace declarations in the result tree.

The value of an attribute of a literal result element is interpreted as an attribute value template: it can contain expressions contained in curly braces ({}).

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. This applies to:

the namespace URI in the expanded-name of a literal result element in the stylesheet
the namespace URI in the expanded-name of an attribute specified on a literal result element in the stylesheet
the string-value of a namespace node on a literal result element in the stylesheet

 <xsl:namespace-alias stylesheet-prefix = prefix | "#default" result-prefix = prefix | "#default" />

A stylesheet can use the xsl:namespace-alias element to declare that one namespace URI is an alias for another namespace URI. When a literal namespace URI has been declared to be an alias for another namespace URI, then the namespace URI in the result tree will be the namespace URI that the literal namespace URI is an alias for, instead of the literal namespace URI itself. The xsl:namespace-alias element declares that the namespace URI bound to the prefix specified by the stylesheet-prefix attribute is an alias for the namespace URI bound to the prefix specified by the result-prefix attribute. 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. It is an error if there is more than one such declaration. An XSLT processor may signal the error; if it does not signal the error, it must recover by choosing, from amongst the declarations with the highest import precedence, the one that occurs last in the stylesheet.

When literal result elements are being used to create element, attribute, or namespace nodes that use the XSLT namespace URI, the stylesheet must use an alias. For example, the stylesheet

<xsl:stylesheet
  version="1.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:fo="http://www.w3.org/1999/XSL/Format"
  xmlns:axsl="http://www.w3.org/1999/XSL/TransformAlias">

<xsl:namespace-alias stylesheet-prefix="axsl" result-prefix="xsl"/>

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

NOTE: It may be necessary also to use aliases for namespaces other than the XSLT namespace URI. For example, 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.

7.1.2 Creating Elements with `xsl:element`

 <xsl:element name = { qname } namespace = { uri-reference } use-attribute-sets = qnames>  </xsl:element>

The xsl:element element allows an element to be created with a computed name. The expanded-name of the element to be created is specified by a required name attribute and an optional namespace attribute. The content of the xsl:element element is a template for the attributes and children of the created element.

The name attribute is interpreted as an attribute value template. It is an error if the string that results from instantiating the attribute value template is not a QName. An XSLT processor may signal the error; if it does not signal the error, then it must recover by making the result of instantiating the xsl:element element be the sequence of nodes created by instantiating the content of the xsl:element element, excluding any initial attribute nodes. If the namespace attribute is not present then the QName is expanded into an expanded-name using the namespace declarations in effect for the xsl:element element, including any default namespace declaration.

If the namespace attribute is present, then it also is interpreted as an attribute value template. The string that results from instantiating the attribute value template should be a URI reference. It is not an error if the string is not a syntactically legal URI reference. If the string is empty, then the expanded-name of the element has a null namespace URI. Otherwise, the string is used as the namespace URI of the expanded-name of the element to be created. The local part of the QName specified by the name attribute is used as the local part of the expanded-name of the element to be created.

XSLT processors may make use of the prefix of the QName specified in the name attribute when selecting the prefix used for outputting the created element as XML; however, they are not required to do so.

7.1.3 Creating Attributes with `xsl:attribute`

 <xsl:attribute name = { qname } namespace = { uri-reference }>  </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. The expanded-name of the attribute to be created is specified by a required name attribute and an optional namespace attribute. Instantiating an xsl:attribute element adds an attribute node to the containing result element node. The content of the xsl:attribute element is a template for the value of the created attribute.

The name attribute is interpreted as an attribute value template. It is an error if the string that results from instantiating the attribute value template is not a QName or is the string xmlns. An XSLT processor may signal the error; if it does not signal the error, it must recover by not adding the attribute to the result tree. If the namespace attribute is not present, then the QName is expanded into an expanded-name 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 also is interpreted as an attribute value template. The string that results from instantiating it should be a URI reference. It is not an error if the string is not a syntactically legal URI reference. If the string is empty, then the expanded-name of the attribute has a null namespace URI. Otherwise, the string is used as the namespace URI of the expanded-name of the attribute to be created. The local part of the QName specified by the name attribute is used as the local part of the expanded-name of the attribute to be created.

XSLT processors may make use of the prefix of the QName specified in the name attribute when selecting the prefix used for outputting the created attribute as XML; however, they are not required to do so and, if the prefix is xmlns, they must not do so. Thus, although it is not an error to do:

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

it will not result in a namespace declaration being output.

Adding an attribute to an element replaces any existing attribute of that element with the same expanded-name.

The following are all errors:

Adding an attribute to an element after children have been added to it; implementations may either signal the error or ignore the attribute.
Adding an attribute to a node that is not an element; implementations may either signal the error or ignore the attribute.
Creating nodes other than text nodes during the instantiation of the content of the xsl:attribute element; implementations may either signal the error or ignore the offending nodes together with their content.

NOTE: When an xsl:attribute contains a text node with a newline, then the XML output must contain a character reference. For example,
<xsl:attribute name="a">x
y</xsl:attribute>
will result in the output
a="x&#xA;y"
(or with any equivalent character reference). The XML output cannot be
a="x
y"
This is because XML 1.0 requires newline characters in attribute values to be normalized into spaces but requires character references to newline characters not to be normalized. The attribute values in the data model represent the attribute value after normalization. If a newline occurring in an attribute value in the tree were output as a newline character rather than as character reference, then the attribute value in the tree created by reparsing the XML would contain a space not a newline, which would mean that the tree had not been output correctly.

7.1.4 Named Attribute Sets

 <xsl:attribute-set name = qname use-attribute-sets = qnames>  </xsl:attribute-set>

The xsl:attribute-set element defines a named set of attributes. The name attribute specifies the name of the attribute set. The value of the name attribute is a QName, which is expanded as described in [2.4 Qualified Names]. The content of the xsl:attribute-set element consists of zero or more xsl:attribute elements that specify the attributes in the set.

Attribute sets are used by specifying a use-attribute-sets attribute on xsl:element, xsl:copy (see [7.5 Copying]) or xsl:attribute-set elements. The value of the use-attribute-sets attribute is a whitespace-separated list of names of attribute sets. Each name is specified as a QName, which is expanded as described in [2.4 Qualified Names]. Specifying a use-attribute-sets attribute is equivalent to adding xsl:attribute elements for each of the attributes in each of the named attribute sets to the beginning of the content of the element with the use-attribute-sets attribute, in the same order in which the names of the attribute sets are specified in the use-attribute-sets attribute. It is an error if use of use-attribute-sets attributes on xsl:attribute-set elements causes an attribute set to directly or indirectly use itself.

Attribute sets can also be used by specifying an xsl:use-attribute-sets attribute on a literal result element. The value of the xsl:use-attribute-sets attribute is a whitespace-separated list of names of attribute sets. The xsl:use-attribute-sets attribute has the same effect as the use-attribute-sets attribute on xsl:element with the additional rule that attributes specified on the literal result element itself are treated as if they were specified by xsl:attribute elements before any actual xsl:attribute elements but after any xsl:attribute elements implied by the xsl:use-attribute-sets attribute. Thus, for a literal result element, attributes from attribute sets named in an xsl:use-attribute-sets attribute will be added first, in the order listed in the attribute; next, attributes specified on the literal result element will be added; finally, any attributes specified by xsl:attribute elements will be added. Since adding an attribute to an element replaces any existing attribute of that element with the same name, this means that attributes specified in attribute sets can be overridden by attributes specified on the literal result element itself.

The template within each xsl:attribute element in an xsl:attribute-set element is instantiated each time the attribute set is used; it is instantiated using the same current node and current node list as is used for instantiating the element bearing the use-attribute-sets or xsl:use-attribute-sets attribute. However, it is the position in the stylesheet of the xsl:attribute element rather than of the element bearing the use-attribute-sets or xsl:use-attribute-sets attribute that determines which variable bindings are visible (see [11 Variables and Parameters]); thus, only variables and parameters declared by top-level xsl:variable and xsl:param elements are visible.

The following example creates a named attribute set title-style and uses it in a template rule.

<xsl:template match="chapter/heading">
  <fo:block quadding="start" 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>

Multiple definitions of an attribute set with the same expanded-name are merged. An attribute from a definition that has higher import precedence takes precedence over an attribute from a definition that has lower import precedence. It is an error if there are two attribute sets that have the same expanded-name and equal import precedence and that both contain the same attribute, unless there is a definition of the attribute set with higher import precedence that also contains the attribute. An XSLT processor may signal the error; if it does not signal the error, it must recover by choosing from amongst the definitions that specify the attribute that have the highest import precedence the one that was specified last in the stylesheet. Where the attributes in an attribute set were specified is relevant only in merging the attributes into the attribute set; it makes no difference when the attribute set is used. For each attribute set name occurring in a use-attribute-sets attribute on an xsl:attribute-set element, all definitions of an attribute set with that name must be merged before the use-attribute-sets attribute is replaced by the equivalent sequence of xsl:attribute child elements. Any use-attribute-sets attribute on an xsl:attribute-set element must be replaced by the equivalent sequence of xsl:attribute child elements before that xsl:attribute-set element is merged with other xsl:attribute-set elements with the same expanded-name. When xsl:attribute-set elements with the same expanded-name are merged, any xsl:attribute child elements added to replace a use-attribute-sets attribute are treated exactly as if they had originally been specified in the stylesheet as child elements.

7.2 Creating Text

A template can also contain text nodes. Each text node in a template remaining after whitespace has been stripped as specified in [3.4 Whitespace Stripping] will create a text node with the same string-value in the result tree. Adjacent text nodes in the result tree are automatically merged.

Note that text is processed at the tree level. Thus, markup of < 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 < (or an equivalent character reference) when the result tree is externalized as an XML document (unless output escaping is disabled as described in [16.4 Disabling Output Escaping]).

 <xsl:text disable-output-escaping = "yes" | "no">  </xsl:text>

Literal data characters may also be wrapped in an xsl:text element. This wrapping may change what whitespace characters are stripped (see [3.4 Whitespace Stripping]) but does not affect how the characters are handled by the XSLT processor thereafter.

NOTE: The xml:lang and xml:space attributes are not treated specially by XSLT. In particular,

it is the responsibility of the stylesheet author explicitly to generate any xml:lang or xml:space attributes that are needed in the result;

specifying an xml:lang or xml:space attribute on an element in the XSLT namespace will not cause any xml:lang or xml:space attributes to appear in the result.

7.3 Creating Processing Instructions

 <xsl:processing-instruction name = { ncname }>  </xsl:processing-instruction>

The xsl:processing-instruction element is instantiated to create a processing instruction node. The content of the xsl:processing-instruction element is a template for the string-value of the 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.

For example, this

<xsl:processing-instruction name="xml-stylesheet">href="book.css" type="text/css"</xsl:processing-instruction>

would create the processing instruction

<?xml-stylesheet href="book.css" type="text/css"?>

It is an error if the string that results from instantiating the name attribute is not both an NCName and a PITarget. An XSLT processor may signal the error; if it does not signal the error, it must recover by not adding the processing instruction to the result tree.

NOTE: This means that xsl:processing-instruction cannot be used to output an XML declaration. The xsl:output element should be used instead (see [16 Output]).

It is an error if instantiating the content of xsl:processing-instruction creates nodes other than text nodes. An XSLT processor may signal the error; if it does not signal the error, it must recover by ignoring the offending nodes together with their content.

It is an error if the result of instantiating the content of the xsl:processing-instruction contains the string ?>. An XSLT processor may signal the error; if it does not signal the error, it must recover by inserting a space after any occurrence of ? that is followed by a >.

7.4 Creating Comments

 <xsl:comment>  </xsl:comment>

The xsl:comment element is instantiated to create a comment node in the result tree. The content of the xsl:comment element is a template for the string-value of the 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!-->

It is an error if instantiating the content of xsl:comment creates nodes other than text nodes. An XSLT processor may signal the error; if it does not signal the error, it must recover by ignoring the offending nodes together with their content.

It is an error if the result of instantiating the content of the xsl:comment contains the string -- or ends with -. An XSLT processor may signal the error; if it does not signal the error, it must recover by inserting a space after any occurrence of - that is followed by another - or that ends the comment.

7.5 Copying

 <xsl:copy use-attribute-sets = qnames>  </xsl:copy>

The xsl:copy element provides an easy way of copying the current node. Instantiating the xsl:copy element creates a copy of the current node. The namespace nodes of the current node are automatically copied as well, but the attributes and children of the node are not automatically copied. The content of the xsl:copy element is a template for the attributes and children of the created node; the content is instantiated only for nodes of types that can have attributes or children (i.e. root nodes and element nodes).

The xsl:copy element may have a use-attribute-sets attribute (see [7.1.4 Named Attribute Sets]). This is used only when copying element nodes.

The root node is treated specially because the root node of the result tree is created implicitly. When the current node is the root node, xsl:copy will not create a root node, but will just use the content template.

For example, 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>

When the current node is an attribute, then if it would be an error to use xsl:attribute to create an attribute with the same name as the current node, then it is also an error to use xsl:copy (see [7.1.3 Creating Attributes with xsl:attribute]).

When the current node is a namespace node, then copying it adds a namespace node to the containing node in the result tree. It is an error if this containing node is not an element; implementations may either signal the error or ignore the namespace node. It is an error to add a namespace node to an element after children have been added to it or after attributes have been added to it; implementations may either signal an error or ignore the namespace node. It is an error to add a namespace node to an element if the element already has a namespace node with the same name, unless both namespace nodes have the same string-value, in which case the duplicate is ignored. It is an error to add a namespace node to an element if the namespace node has a null name and the element has a null namespace URI.

The following example shows how xml:lang attributes can be easily copied through from source to result. If a stylesheet defines the following named template:

<xsl:template name="apply-templates-copy-lang">
 <xsl:for-each select="@xml:lang">
   <xsl:copy/>
 </xsl:for-each>
 <xsl:apply-templates/>
</xsl:template>

then it can simply do

<xsl:call-template name="apply-templates-copy-lang"/>

instead of

<xsl:apply-templates/>

when it wants to copy the xml:lang attribute.

7.6 Computing Generated Text

Within a template, the xsl:value-of element 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 element does this with an expression that is specified as the value of the select attribute. Expressions can also be used inside attribute values of literal result elements by enclosing the expression in curly braces ({}).

7.6.1 Generating Text with `xsl:value-of`

 <xsl:value-of select = string-expression disable-output-escaping = "yes" | "no" />

The xsl:value-of element is instantiated to create a text node in the result tree. The required select attribute is an expression; this expression is evaluated and the resulting object is converted to a string as if by a call to the string function. The string specifies the string-value of the created text node. If the string is empty, no text node will be created. The created text node will be merged with any adjacent text nodes.

The xsl:copy-of element can be used to copy a node-set over to the result tree without converting it to a string. See [11.3 Using Values of Variables and Parameters with xsl:copy-of].

For example, the following creates an HTML paragraph from a person element with given-name and family-name attributes. The paragraph will contain the value of the given-name attribute of the current node followed by a space and the value of the family-name attribute of the current node.

<xsl:template match="person">
  <p>
   <xsl:value-of select="@given-name"/>
   <xsl:text> </xsl:text>
   <xsl:value-of select="@family-name"/>
  </p>
</xsl:template>

For another example, the following creates an HTML paragraph from a person element with given-name and family-name children elements. The paragraph will contain the string-value of the first given-name child element of the current node followed by a space and the string-value of the first family-name child element of the current node.

<xsl:template match="person">
  <p>
   <xsl:value-of select="given-name"/>
   <xsl:text> </xsl:text>
   <xsl:value-of select="family-name"/>
  </p>
</xsl:template>

The following precedes each procedure element with a paragraph containing the security level of the procedure. It assumes that the security level that applies to a procedure is determined by a security attribute on the procedure element or on an ancestor element of the procedure. It also assumes that if more than one such element has a security attribute then the security level is determined by the element that is closest to the procedure.

<xsl:template match="procedure">
  <fo:block>
    <xsl:value-of select="ancestor-or-self::*[@security][1]/@security"/>
  </fo:block>
  <xsl:apply-templates/>
</xsl:template>

7.6.2 Attribute Value Templates

In an attribute value that is interpreted 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 braces ({}). The attribute value template is instantiated by replacing the expression together with surrounding curly braces by the result of evaluating the expression and converting the resulting object to a string as if by a call to the string function. Curly braces are not recognized in an attribute value in an XSLT stylesheet unless the attribute is specifically stated to be one that is interpreted as an attribute value template; in an element syntax summary, the value of such attributes is surrounded by curly braces.

NOTE: Not all attributes are interpreted as attribute value templates. Attributes whose value is an expression or pattern, attributes of top-level elements and attributes that refer to named XSLT objects are not interpreted as attribute value templates. In addition, xmlns attributes are not interpreted as attribute value templates; it would not be conformant with the XML Namespaces Recommendation to do this.

The following example creates an img result element from a photograph element in the source; the value of the src attribute of the img element is computed from the value of the image-dir variable and the string-value of the href child of the photograph element; the value of the width attribute of the img element is computed from the value of the width attribute of the size child of the photograph element:

<xsl:variable name="image-dir">/images</xsl:variable>

<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"/>

When an attribute value template is instantiated, a double left or right curly brace outside an expression will be replaced by a single curly brace. It is an error if a right curly brace occurs in an attribute value template outside an expression without being followed by a second right curly brace. A right curly brace inside a Literal in an expression is not recognized as terminating the expression.

Curly braces are not recognized recursively inside expressions. For example:

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

is not allowed. Instead, use simply:

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

7.7 Numbering

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

The xsl:number element is used to insert a formatted number into the result tree. The number to be inserted may be specified by an expression. The value attribute contains an expression. The expression is evaluated and the resulting object is converted to a number as if by a call to the number function. It is an error if the number is NaN, infinite or less than 0.5; an XSLT processor may signal the error; if it does not signal the error, it must recover by converting the number to a string as if by a call to the string function and inserting the resulting string into the result tree. Otherwise, the number is rounded to an integer and then converted to a string using the attributes specified in [7.7.1 Number to String Conversion Attributes]; in this context, the value of each of these attributes is interpreted as an attribute value template. After conversion, the resulting string is inserted in the result tree. For example, 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>

If no value attribute is specified, then the xsl:number element inserts a number based on the position of the current node in the source tree. The following attributes control how the current node is to be numbered:

The level attribute specifies what levels of the source tree should be considered; it has the values single, multiple or any. The default is single.
The count attribute is a pattern that specifies what nodes should 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 type as the current node and, if the current node has an expanded-name, with the same expanded-name as the current node.
The from attribute is a pattern that specifies where counting starts.

In addition, the attributes specified in [7.7.1 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 list of positive integers using the level, count and from attributes:

When level="single", it goes up to the first node in the ancestor-or-self axis that matches the count pattern, and constructs a list of length one containing one plus the number of preceding siblings of that ancestor that match the count pattern. If there is no such ancestor, it constructs an empty list. If the from attribute is specified, then the only ancestors that are searched are those that are descendants of the nearest ancestor that matches the from pattern. Preceding siblings has the same meaning here as with the preceding-sibling axis.
When level="multiple", it constructs a list of all ancestors of the current node in document order followed by the element itself; it then selects from the list those nodes that match the count pattern; it then maps each node in the list to one plus the number of preceding siblings of that node that match the count pattern. If the from attribute is specified, then the only ancestors that are searched are those that are descendants of the nearest ancestor that matches the from pattern. Preceding siblings has the same meaning here as with the preceding-sibling axis.
When level="any", it constructs a list of length one containing the number of nodes that match the count pattern and belong to the set containing the current node and all nodes at any level of the document that are before the current node in document order, excluding any namespace and attribute nodes (in other words the union of the members of the preceding and ancestor-or-self axes). If there are no matching nodes, it constructs an empty list. If the from attribute is specified, then only nodes after the first node before the current node that match the from pattern are considered.

The list of numbers is then converted into a string using the attributes specified in [7.7.1 Number to String Conversion Attributes]; in this context, the value of each of these attributes is interpreted as an attribute value template. After conversion, the resulting string is inserted in the result tree.

The following would 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>

The following two rules would 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.

<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>

The following 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>

The following example would number H4 elements in HTML with a three-part label:

<xsl:template match="H4">
 <fo:block>
   <xsl:number level="any" from="H1" count="H2"/>
   <xsl:text>.</xsl:text>
   <xsl:number level="any" from="H2" count="H3"/>
   <xsl:text>.</xsl:text>
   <xsl:number level="any" from="H3" count="H4"/>
   <xsl:text> </xsl:text>
   <xsl:apply-templates/>
 </fo:block>
</xsl:template>

7.7.1 Number to String Conversion Attributes

The following attributes are used to control conversion of a list 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) specify the format to be used for each number in the list. 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 list. The nth format token will be used to format the nth number in the list. 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. The format token specifies the string to be used to represent the number 1. 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 . (a period character).

Format tokens are a superset of the allowed values for the type attribute for the OL element in HTML 4.0 and 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. 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 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 ....
Any other format token indicates a numbering sequence that starts with that token. If an implementation does not support a numbering sequence that starts with that token, it must use a format token of 1.

When numbering with an alphabetic sequence, the lang attribute specifies which language's alphabet is to be used; it has the same range of values as xml:lang [XML]; if no lang value is specified, the language should be determined from the system environment. Implementers should document for which languages they support numbering.

NOTE: Implementers should not make any assumptions about how numbering works in particular languages and should properly research the languages that they wish to support. The numbering conventions of many languages are very different from English.

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: It is possible for two conforming XSLT processors not to convert a number to exactly the same string. Some XSLT processors may not support some languages. Furthermore, there may be variations possible in the way conversions are performed for any particular language that are not specifiable by the attributes on xsl:number. Future versions of XSLT may provide additional attributes to provide control over these variations. Implementations may also use implementation-specific namespaced attributes on xsl:number for this.

The grouping-separator attribute gives the separator used as a grouping (e.g. 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. If only one of the grouping-separator and grouping-size attributes is specified, then it is ignored.

Here are some examples of conversion specifications:

format="ア" specifies Katakana numbering
format="イ" specifies Katakana numbering in the "iroha" order
format="๑" specifies numbering with Thai digits
format="א" letter-value="traditional" specifies "traditional" Hebrew numbering
format="ა" letter-value="traditional" specifies Georgian numbering
format="α" letter-value="traditional" specifies "classical" Greek numbering
format="а" letter-value="traditional" specifies Old Slavic numbering

8 Repetition

 <xsl:for-each select = node-set-expression>  </xsl:for-each>

When the result has a known regular structure, it is useful to be able to specify directly the template for selected nodes. The xsl:for-each instruction contains a template, which is instantiated for each node selected by the expression specified by the select attribute. The select attribute is required. The expression must evaluate to a node-set. The template is instantiated with the selected node as the current node, and with a list of all of the selected nodes as the current node list. The nodes are processed in document order, unless a sorting specification is present (see [10 Sorting]).

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>

9 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.

9.1 Conditional Processing with `xsl:if`

 <xsl:if test = boolean-expression>  </xsl:if>

The xsl:if element has a test attribute, which specifies an expression. The content is a template. The expression is evaluated and the resulting object is converted to a boolean as if by a call to the boolean function. If the result is true, then the content template is instantiated; otherwise, nothing is created. 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>

9.2 Conditional Processing with `xsl:choose`

 <xsl:choose>  </xsl:choose>

<xsl:when test = boolean-expression>  </xsl:when>

<xsl:otherwise>  </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 template. When an xsl:choose element is processed, each of the xsl:when elements is tested in turn, by evaluating the expression and converting the resulting object to a boolean as if by a call to the boolean function. The content of the first, and only the first, xsl:when element whose test is true is instantiated. If no xsl:when is true, the content of the xsl:otherwise element is instantiated. If no xsl:when element is true, and no xsl:otherwise element is present, nothing is created.

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>

10 Sorting

<xsl:sort select = string-expression lang = { nmtoken } data-type = { "text" | "number" | qname-but-not-ncname } order = { "ascending" | "descending" } case-order = { "upper-first" | "lower-first" } />

Sorting is specified by adding xsl:sort elements as children of an xsl:apply-templates or xsl:for-each element. The first xsl:sort child specifies the primary sort key, the second xsl:sort child specifies the secondary sort key and so on. When an xsl:apply-templates or xsl:for-each element has one or more xsl:sort children, then instead of processing the selected nodes in document order, it sorts the nodes according to the specified sort keys and then processes them in sorted order. When used in xsl:for-each, xsl:sort elements must occur first. When a template is instantiated by xsl:apply-templates and xsl:for-each, the current node list consists of the complete list of nodes being processed in sorted order.

xsl:sort has a select attribute whose value is an expression. For each node to be processed, the expression is evaluated with that node as the current node and with the complete list of nodes being processed in document order as the current node list. The resulting object is converted to a string as if by a call to the string function; this string is used as the sort key for that node. The default value of the select attribute is ., which will cause the string-value of the current node to be used as the sort key.

This string serves as a sort key for the node. The following optional attributes on xsl:sort control how the list of sort keys are sorted; the values of all of these attributes are interpreted as attribute value templates.

order specifies whether the strings should be sorted in ascending or descending order; ascending specifies ascending order; descending specifies descending order; the default is ascending
lang specifies the language of the sort keys; it has the same range of values as xml:lang [XML]; if no lang value is specified, the language should be determined from the system environment
data-type specifies the data type of the strings; the following values are allowed:
- text specifies that the sort keys should be sorted lexicographically in the culturally correct manner for the language specified by lang
- number specifies that the sort keys should be converted to numbers and then sorted according to the numeric value; the sort key is converted to a number as if by a call to the number function; the lang attribute is ignored; in ascending order a NaN precedes all other numeric values and in descending order it follows them.
- a QName with a prefix is expanded into an expanded-name as described in [2.4 Qualified Names]; the expanded-name identifies the data-type; the behavior in this case is not specified by this document
The default value is text.

NOTE: The XSL Working Group plans that future versions of XSLT will leverage XML Schemas to define further values for this attribute.
case-order has the value upper-first or lower-first; this applies when data-type="text", and specifies that in ascending order upper-case letters should sort before lower-case letters or vice-versa respectively. For example, if lang="en", then A a B b are sorted in ascending order with case-order="upper-first" and a A b B are sorted with case-order="lower-first". In descending order, the effect is reversed. For example, if lang="en", then b B a A are sorted in descending order with case-order="upper-first". The default value is language dependent.

NOTE: It is possible for two conforming XSLT processors not to sort exactly the same. Some XSLT processors may not support some languages. Furthermore, there may be variations possible in the sorting of any particular language that are not specified by the attributes on xsl:sort, for example, whether Hiragana or Katakana is sorted first in Japanese. Future versions of XSLT may provide additional attributes to provide control over these variations. Implementations may also use implementation-specific namespaced attributes on xsl:sort for this.

NOTE: It is recommended that implementers consult [UNICODE TR10] for information on internationalized sorting.

The sort must be stable: in the sorted list of nodes, any sub list that has sort keys that all compare equal must be in document 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>

11 Variables and Parameters

  <xsl:variable name = qname select = expression>  </xsl:variable>

 <xsl:param name = qname select = expression>  </xsl:param>

A variable is a name that may be bound to a value. The value to which a variable is bound (the value of the variable) can be an object of any of the types that can be returned by expressions. There are two elements that can be used to bind variables: xsl:variable and xsl:param. The difference is that the value specified on the xsl:param variable is only a default value for the binding; when the template or stylesheet within which the xsl:param element occurs is invoked, parameters may be passed that are used in place of the default values.

Both xsl:variable and xsl:param have 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 [2.4 Qualified Names].

For any use of these variable-binding elements, there is a region of the stylesheet tree within which the binding is visible. The set of variable bindings in scope for an expression consists of those bindings that are visible at the point in the stylesheet where the expression occurs.

11.1 Result Tree Fragments

Variables introduce an additional data-type into the expression language. This additional data type is called result tree fragment. A variable may be bound to a result tree fragment instead of one of the four basic XPath data-types (string, number, boolean, node-set). A result tree fragment represents a fragment of the result tree. A result tree fragment is treated equivalently to a node-set that contains just a single root node. However, the operations permitted on a result tree fragment are a subset of those permitted on a node-set. An operation is permitted on a result tree fragment only if that operation would be permitted on a string (the operation on the string may involve first converting the string to a number or boolean). In particular, it is not permitted to use the /, //, and [] operators on result tree fragments. When a permitted operation is performed on a result tree fragment, it is performed exactly as it would be on the equivalent node-set.

When a result tree fragment is copied into the result tree (see [11.3 Using Values of Variables and Parameters with xsl:copy-of]), then all the nodes that are children of the root node in the equivalent node-set are added in sequence to the result tree.

Expressions can only return values of type result tree fragment by referencing variables of type result tree fragment or calling extension functions that return a result tree fragment or getting a system property whose value is a result tree fragment.

11.2 Values of Variables and Parameters

A variable-binding element can specify the value of the variable in three alternative ways.

If the variable-binding element has a select attribute, then the value of the attribute must be an expression and the value of the variable is the object that results from evaluating the expression. In this case, the content must be empty.
If the variable-binding element does not have a select attribute and has non-empty content (i.e. the variable-binding element has one or more child nodes), then the content of the variable-binding element specifies the value. The content of the variable-binding element is a template, which is instantiated to give the value of the variable. The value is a result tree fragment equivalent to a node-set containing just a single root node having as children the sequence of nodes produced by instantiating the template. The base URI of the nodes in the result tree fragment is the base URI of the variable-binding element.

It is an error if a member of the sequence of nodes created by instantiating the template is an attribute node or a namespace node, since a root node cannot have an attribute node or a namespace node as a child. An XSLT processor may signal the error; if it does not signal the error, it must recover by not adding the attribute node or namespace node.
If the variable-binding element has empty content and does not have a select attribute, then the value of the variable is an empty string. Thus
```
<xsl:variable name="x"/>
```
is equivalent to
```
<xsl:variable name="x" select="''"/>
```

NOTE: 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="item[$n]"/>
This will output the value of the first item element, because the variable n will be bound to a result tree fragment, not a number. Instead, do either
<xsl:variable name="n" select="2"/>
...
<xsl:value-of select="item[$n]"/>
or
<xsl:variable name="n">2</xsl:variable>
...
<xsl:value-of select="item[position()=$n]"/>

NOTE: One convenient way to specify the empty node-set as the default value of a parameter is:
<xsl:param name="x" select="/.."/>

11.3 Using Values of Variables and Parameters with `xsl:copy-of`

 <xsl:copy-of select = expression />

The xsl:copy-of element can be used to insert a result tree fragment into the result tree, without first converting it to a string as xsl:value-of does (see [7.6.1 Generating Text with xsl:value-of]). The required select attribute contains an expression. When the result of evaluating the expression is a result tree fragment, the complete fragment is copied into the result tree. When the result is a node-set, all the nodes in the set are copied in document order into the result tree; copying an element node copies the attribute nodes, namespace nodes and children of the element node as well as the element node itself; a root node is copied by copying its children. For copying an attribute or namespace node, the same rules apply as with xsl:copy (see [7.5 Copying]). When the result is neither a node-set nor a result tree fragment, the result is converted to a string and then inserted into the result tree, as with xsl:value-of.

11.4 Top-level Variables and Parameters

Both xsl:variable and xsl:param are allowed as top-level elements. A top-level variable-binding element declares a global variable that is visible everywhere (except where it is shadowed by another binding). A top-level xsl:param element declares a parameter to the stylesheet; XSLT does not define the mechanism by which parameters are passed to the stylesheet. If a stylesheet contains more than one binding for a variable of a particular name, then the binding with the highest import precedence is used. It is an error if a stylesheet contains more than one binding of a top-level variable with the same name and same import precedence. At the top-level, the expression or template specifying the variable value is evaluated with the same context as that used to process the root node of the source document: the current node is the root node of the source document and the current node list is a list containing just the root node of the source document. If the template or expression 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. It is an error if it is impossible to do this for all global variable definitions; in other words, it is an error if the definitions are circular.

This example declares a global variable para-font-size, which it references in an attribute value template.

<xsl:variable name="para-font-size">12pt</xsl:variable>

<xsl:template match="para">
 <fo:block font-size="{$para-font-size}">
   <xsl:apply-templates/>
 </fo:block>
</xsl:template>

11.5 Variables and Parameters within Templates

As well as being allowed at the top-level, both xsl:variable and xsl:param are also allowed in templates. xsl:variable is allowed anywhere within a template that an instruction is allowed. In this case, the binding is visible for the descendants of all following siblings that are not xsl:fallback instructions. Note that the binding is not visible for the xsl:variable element itself. xsl:param is allowed as a child at the beginning of an xsl:template element. In this context, the binding is visible for the descendants of all following siblings that are not xsl:fallback instructions. Note that the binding is not visible for the xsl:param element itself.

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 an error if a binding established by an xsl:variable or xsl:param element within a template shadows another binding established by an xsl:variable or xsl:param element also within the template. It is not an error if a binding established by an xsl:variable or xsl:param element in a template shadows another binding established by an xsl:variable or xsl:param top-level element. In this case, the top-level binding will not be visible in the region of the stylesheet where it is shadowed by the other binding. Thus, the following is an error:

<xsl:template name="foo">
<xsl:param name="x" select="1"/>
<xsl:variable name="x" select="2"/>
</xsl:template>

However, the following is allowed:

<xsl:param name="x" select="1"/>
<xsl:template name="foo">
<xsl:variable name="x" select="2"/>
</xsl:template>

NOTE: The nearest equivalent in Java to an xsl:variable element in a template is a final local variable declaration with an initializer. For example,
<xsl:variable name="x" select="'value'"/>
has similar semantics to
final Object x = "value";
XSLT does not provide an equivalent to the Java assignment operator
x = "value";
because this 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.

11.6 Passing Parameters to Templates

<xsl:with-param name = qname select = expression>  </xsl:with-param>

Parameters are passed to templates using the xsl:with-param element. The required name attribute specifies the name of the 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 [2.4 Qualified Names]. xsl:with-param is allowed within both xsl:call-template and xsl:apply-templates. It is an error if a single xsl:call-template or xsl:apply-templates element contains more than one xsl:with-param element with the same name. The value of the parameter is specified in the same way as for xsl:variable and xsl:param. The current node and current node list used for computing the value specified by xsl:with-param element is the same as that used for the xsl:apply-templates or xsl:call-template element within which it occurs. It is not an error to pass a parameter x to a template that does not have an xsl:param element for x; the parameter is simply ignored.

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>

12 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 top-level elements in the stylesheet; this section also describes these elements.

12.1 Multiple Source Documents

Function: node-set document(object, node-set?)

The document function allows access to XML documents other than the main source document.

When the document function has exactly one argument and the argument is a node-set, then the result is the union, for each node in the argument node-set, of the result of calling the document function with the first argument being the string-value of the node, and the second argument being a node-set with the node as its only member. When the document function has two arguments and the first argument is a node-set, then the result is the union, for each node in the argument node-set, of the result of calling the document function with the first argument being the string-value of the node, and with the second argument being the second argument passed to the document function.

When the first argument to the document function is not a node-set, the first argument is converted to a string as if by a call to the string function. This string is treated as a URI reference; the resource identified by the URI is retrieved. The data resulting from the retrieval action is parsed as an XML document and a tree is constructed in accordance with the data model (see [3 Data Model]). If there is an error retrieving the resource, then the XSLT processor may signal an error; if it does not signal an error, it must recover by returning an empty node-set. One possible kind of retrieval error is that the XSLT processor does not support the URI scheme used by the URI. An XSLT processor is not required to support any particular URI schemes. The documentation for an XSLT processor should specify which URI schemes the XSLT processor supports.

If the URI reference does not contain a fragment identifier, then a node-set containing just the root node of the document is returned. If the URI reference does contain a fragment identifier, the function returns a node-set containing the nodes in the tree identified by the fragment identifier of the URI reference. The semantics of the fragment identifier are dependent on the media type of the result of retrieving the URI. If there is an error in processing the fragment identifier, the XSLT processor may signal the error; if it does not signal the error, it must recover by returning an empty node-set. Possible errors include:

The fragment identifier identifies something that cannot be represented by an XSLT node-set (such as a range of characters within a text node).
The XSLT processor does not support fragment identifiers for the media-type of the retrieval result. An XSLT processor is not required to support any particular media types. The documentation for an XSLT processor should specify for which media types the XSLT processor supports fragment identifiers.

The data resulting from the retrieval action is parsed as an XML document regardless of the media type of the retrieval result; if the top-level media type is text, then it is parsed in the same way as if the media type were text/xml; otherwise, it is parsed in the same way as if the media type were application/xml.

NOTE: Since there is no top-level xml media type, data with a media type other than text/xml or application/xml may in fact be XML.

The URI reference may be relative. The base URI (see [3.2 Base URI]) of the node in the second argument node-set that is first in document order is used as the base URI for resolving the relative URI into an absolute URI. It is an error if the second argument node-set is empty and the URI reference is relative; the XSLT processor may signal the error; if it does not signal an error, it must recover by returning an empty node-set. If the second argument is omitted, then it defaults to the node in the stylesheet that contains the expression that includes the call to the document function. Note that a zero-length URI reference is a reference to the document relative to which the URI reference is being resolved; thus document("") refers to the root node of the stylesheet; the tree representation of the stylesheet is exactly the same as if the XML document containing the stylesheet was the initial source document.

Two documents are treated as the same document if they are identified by the same URI. The URI used for the comparison is the absolute URI into which any relative URI was resolved and does not include any fragment identifier. One root node is treated as the same node as another root node if the two nodes are from the same document. Thus, the following expression will always be true:

generate-id(document("foo.xml"))=generate-id(document("foo.xml"))

The document function gives rise to the possibility that a node-set may contain nodes from more than one document. With such a node-set, the relative document order of two nodes in the same document is the normal document order defined by XPath [XPath]. The relative document order of two nodes in different documents is determined by an implementation-dependent ordering of the documents containing the two nodes. There are no constraints on how the implementation orders documents other than that it must do so consistently: an implementation must always use the same order for the same set of documents.

12.2 Keys

Keys provide a way to work with documents that contain an implicit cross-reference structure. The ID, IDREF and IDREFS attribute types in XML provide a mechanism to allow XML documents to make their cross-reference explicit. XSLT supports this through the XPath id function. However, this mechanism has a number of limitations:

ID attributes must be declared as such in the DTD. If an ID attribute is declared as an ID attribute only in the external DTD subset, then it will be recognized as an ID attribute only if the XML processor reads the external DTD subset. However, XML does not require XML processors to read the external DTD, and they may well choose not to do so, especially if the document is declared standalone="yes".
A document can contain only a single set of unique IDs. There cannot be separate independent sets of unique IDs.
The ID of an element can only be specified in an attribute; it cannot be specified by the content of the element, or by a child element.
An ID is constrained to be an XML name. For example, it cannot contain spaces.
An element can have at most one ID.
At most one element can have a particular ID.

Because of these limitations XML documents sometimes contain a cross-reference structure that is not explicitly declared by ID/IDREF/IDREFS attributes.

A key is a triple containing:

the node which has the key
the name of the key (an expanded-name)
the value of the key (a string)

A stylesheet declares a set of keys for each document using the xsl:key element. When this set of keys contains a member with node x, name y and value z, we say that node x has a key with name y and value z.

Thus, a key is a kind of generalized ID, which is not subject to the same limitations as an XML ID:

Keys are declared in the stylesheet using xsl:key elements.
A key has a name as well as a value; each key name may be thought of as distinguishing a separate, independent space of identifiers.
The value of a named key for an element may be specified in any convenient place; for example, in an attribute, in a child element or in content. An XPath expression is used to specify where to find the value for a particular named key.
The value of a key can be an arbitrary string; it is not constrained to be a name.
There can be multiple keys in a document with the same node, same key name, but different key values.
There can be multiple keys in a document with the same key name, same key value, but different nodes.

 <xsl:key name = qname match = pattern use = expression />

The xsl:key element 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 [2.4 Qualified Names]. The match attribute is a Pattern; an xsl:key element gives information about the keys of any node that matches the pattern specified in the match attribute. The use attribute is an expression specifying the values of the key; the expression is evaluated once for each node that matches the pattern. If the result is a node-set, then for each node in the node-set, the node that matches the pattern has a key of the specified name whose value is the string-value of the node in the node-set; otherwise, the result is converted to a string, and the node that matches the pattern has a key of the specified name with value equal to that string. Thus, a node x has a key with name y and value z if and only if there is an xsl:key element such that:

x matches the pattern specified in the match attribute of the xsl:key element;
the value of the name attribute of the xsl:key element is equal to y; and
when the expression specified in the use attribute of the xsl:key element is evaluated with x as the current node and with a node list containing just x as the current node list resulting in an object u, then either z is equal to the result of converting u to a string as if by a call to the string function, or u is a node-set and z is equal to the string-value of one or more of the nodes in u.

Note also that there may be more than one xsl:key element that matches a given node; all of the matching xsl:key elements are used, even if they do not have the same import precedence.

It is an error for the value of either the use attribute or the match attribute to contain a VariableReference or a call to the key function.

Function: node-set key(string, object)

The key function does for keys what the id function does for IDs. The first argument specifies the name of the key. The value of the argument must be a QName, which is expanded as described in [2.4 Qualified Names]. When the second argument to the key function is of type node-set, then the result is the union of the result of applying the key function to the string-value of each of the nodes in the argument node-set. When the second argument to key is of any other type, the argument is converted to a string as if by a call to the string function; it returns a node-set containing the nodes in the same document as the context node that have a value for the named key equal to this string.

For example, given a declaration

<xsl:key name="idkey" match="div" use="@id"/>

an expression key("idkey",@ref) will return the same node-set 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 current node contains no whitespace.

Suppose a document describing a function library uses a prototype element to define functions

<prototype name="key" return-type="node-set">
<arg type="string"/>
<arg type="object"/>
</prototype>

and a function element to refer to function names

<function>key</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 always returns nodes that are in the same document as the current node; to retrieve a key from any other document, it is necessary first to change the current node. 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:for-each select="document('bib.xml')">
    <xsl:apply-templates select="key('bib',$name)"/>
  </xsl:for-each>
</xsl:template>

12.3 Number Formatting

Function: string format-number(number, string, string?)

The format-number function converts its first argument to a string using the format pattern string specified by the second argument and the decimal-format named by the third argument, or the default decimal-format, if there is no third argument. The format pattern string is in the syntax specified by the JDK 1.1 DecimalFormat class. The format pattern string is in a localized notation: the decimal-format determines what characters have a special meaning in the pattern (with the exception of the quote character, which is not localized). The format pattern must not contain the currency sign (#x00A4); support for this feature was added after the initial release of JDK 1.1. The decimal-format name must be a QName, which is expanded as described in [2.4 Qualified Names]. It is an error if the stylesheet does not contain a declaration of the decimal-format with the specified expanded-name.

NOTE: Implementations are not required to use the JDK 1.1 implementation, nor are implementations required to be implemented in Java.

NOTE: Stylesheets can use other facilities in XPath to control rounding.

 <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 />

The xsl:decimal-format element declares a decimal-format, which controls the interpretation of a format pattern 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 [2.4 Qualified Names]. It is an 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 other attributes on xsl:decimal-format correspond to the methods on the JDK 1.1 DecimalFormatSymbols class. For each get/set method pair there is an attribute defined for the xsl:decimal-format element.

The following attributes both control the interpretation of characters in the format pattern and specify characters that may appear in the result of formatting the number:

decimal-separator specifies the character used for the decimal sign; the default value is the period character (.)
grouping-separator specifies the character used as a grouping (e.g. thousands) separator; the default value is the comma character (,)
percent specifies the character used as a percent sign; the default value is the percent character (%)
per-mille specifies the character used as a per mille sign; the default value is the Unicode per-mille character (#x2030)
zero-digit specifies the character used as the digit zero; the default value is the digit zero (0)

The following attributes control the interpretation of characters in the format pattern:

digit specifies the character used for a digit in the format pattern; the default value is the number sign character (#)
pattern-separator specifies the character used to separate positive and negative sub patterns in a pattern; 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 to represent infinity; the default value is the string Infinity
NaN specifies the string used to represent the NaN value; the default value is the string NaN
minus-sign specifies the character used as the default minus sign; the default value is the hyphen-minus character (-, #x2D)

12.4 Miscellaneous Additional Functions

Function: node-set current()

The current function returns a node-set that has the current node as its only member. For an outermost expression (an expression not occurring within another expression), the current node is always the same as the context node. Thus,

<xsl:value-of select="current()"/>

means the same as

<xsl:value-of select="."/>

However, within square brackets the current node is usually different from the context node. For example,

<xsl:apply-templates select="//glossary/item[@name=current()/@ref]"/>

will process all item elements that have a glossary parent element and that have a name attribute with value equal to the value of the current node's ref attribute. This is different from

<xsl:apply-templates select="//glossary/item[@name=./@ref]"/>

which means the same as

<xsl:apply-templates select="//glossary/item[@name=@ref]"/>

and so would process all item elements that have a glossary parent element and that have a name attribute and a ref attribute with the same value.

It is an error to use the current function in a pattern.

Function: string unparsed-entity-uri(string)

The unparsed-entity-uri returns the URI of the unparsed entity with the specified name in the same document as the context node (see [3.3 Unparsed Entities]). It returns the empty string if there is no such entity.

Function: string generate-id(node-set?)

The generate-id function returns a string that uniquely identifies the node in the argument node-set that is first in document order. 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 node-set is empty, the empty string is returned. If the argument is omitted, it defaults to the context node.

Function: object system-property(string)

The argument must evaluate to a string that is a QName. The QName is expanded into a name using the namespace declarations in scope for the expression. The system-property function returns an object representing the value of the system property identified by the name. If there is no such system property, the empty string should be 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 XSLT processors implementing the version of XSLT specified by this document, this is the number 1.0
xsl:vendor, a string identifying the vendor of the XSLT processor
xsl:vendor-url, a string containing a URL identifying the vendor of the XSLT processor; typically this is the host page (home page) of the vendor's Web site.

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

13 Messages

 <xsl:message terminate = "yes" | "no">  </xsl:message>

The xsl:message instruction sends a message in a way that is dependent on the XSLT processor. The content of the xsl:message instruction is a template. The xsl:message is instantiated by instantiating the content to create an XML fragment. This XML fragment is the content of the message.

NOTE: An XSLT processor might implement xsl:message by popping up an alert box or by writing to a log file.

If the terminate attribute has the value yes, then the XSLT processor should terminate processing after sending the message. The default value is no.

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>
    <xsl:value-of select="$messages/message[@name=$name]"/>
  </xsl:message>
</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>

14 Extensions

XSLT allows two kinds of extension, extension elements and extension functions.

This version of XSLT does not provide a mechanism for defining implementations of extensions. 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 XSLT processor by which it is being processed has implementations of particular extensions available, and to specify what should happen 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 work with any XSLT implementation.

14.1 Extension Elements

The element extension 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 template, 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 template, non-XSLT top-level elements are not extension elements as defined here, and nothing in this section applies to them.

A namespace is designated as an extension namespace by using an extension-element-prefixes attribute on an xsl:stylesheet element or an xsl:extension-element-prefixes attribute on a literal result element or extension element. The value of both these attributes is a whitespace-separated list of namespace prefixes. The namespace bound to each of the prefixes is designated as an extension namespace. It is an error if there is no namespace bound to the prefix on the element bearing the extension-element-prefixes or 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 within the subtree of the stylesheet rooted at the element bearing the extension-element-prefixes or xsl:extension-element-prefixes attribute; a subtree rooted at an xsl:stylesheet element does not include any stylesheets imported or included by children of that xsl:stylesheet element.

If the XSLT processor does not have an implementation of a particular extension element available, then the element-available function must return false for the name of the element. When such an extension element is instantiated, then the XSLT processor must perform fallback for the element as specified in [15 Fallback]. An XSLT processor must not signal an error merely because a template contains an extension element for which no implementation is available.

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

14.2 Extension Functions

If a FunctionName in a FunctionCall expression is not an NCName (i.e. if it contains a colon), then it is treated as a call to an extension function. The FunctionName is expanded to a name using the namespace declarations from the evaluation context.

If the XSLT processor does not have an implementation of an extension function of a particular name available, then the function-available function must return false for that name. If such an extension function occurs in an expression and the extension function is actually called, the XSLT processor must signal an error. An XSLT processor must not signal an error merely because an expression contains an extension function for which no implementation is available.

If the XSLT processor has an implementation of an extension function of a particular name available, then the function-available function must return true for that name. If such an extension is called, then the XSLT processor must call the implementation passing it the function call arguments; the result returned by the implementation is returned as the result of the function call.

15 Fallback

 <xsl:fallback>  </xsl:fallback>

Normally, instantiating an xsl:fallback element does nothing. However, when an XSLT 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 instantiated in sequence; otherwise, an error must be signaled. The content of an xsl:fallback element is a template.

The following functions can be used with the xsl:choose and xsl:if instructions to explicitly control how a stylesheet should behave if particular elements or functions are not available.

Function: boolean element-available(string)

The argument must evaluate to a string that is a QName. The QName is expanded into an expanded-name 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-name is the name of an instruction. If the expanded-name 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 element. If the expanded-name has a null namespace URI, the element-available function will return false.

Function: boolean function-available(string)

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

16 Output

 <xsl:output method = "xml" | "html" | "text" | qname-but-not-ncname version = nmtoken encoding = string omit-xml-declaration = "yes" | "no" standalone = "yes" | "no" doctype-public = string doctype-system = string cdata-section-elements = qnames indent = "yes" | "no" media-type = string />

An XSLT processor may output the result tree as a sequence of bytes, although it is not required to be able to do so (see [17 Conformance]). The xsl:output element allows stylesheet authors to specify how they wish the result tree to be output. If an XSLT processor outputs the result tree, it should do so as specified by the xsl:output element; however, it is not required to do so.

The xsl:output element is only allowed as a top-level element.

The method attribute on xsl:output identifies the overall method that should be used for outputting the result tree. The value must be a QName. If the QName does not have a prefix, then it identifies a method specified in this document and must be one of xml, html or text. If the QName has a prefix, then the QName is expanded into an expanded-name as described in [2.4 Qualified Names]; the expanded-name 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 root node of the result tree has an element child,
the expanded-name of the first element child of the root node (i.e. the document element) of the result tree has local part html (in any combination of upper and lower case) and a null namespace URI, and
any text nodes preceding the first element child of the root node of the result tree contain only whitespace characters,

then the default output method is html; otherwise, the default output method is xml. The default output method should be 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:

version specifies the version of the output method
indent specifies whether the XSLT processor may add additional whitespace when outputting the result tree; the value must be yes or no
encoding specifies the preferred character encoding that the XSLT processor should use to encode sequences of characters as sequences of bytes; the value of the attribute should be treated case-insensitively; the value must contain only characters in the range #x21 to #x7E (i.e. printable ASCII characters); the value should either be a charset registered with the Internet Assigned Numbers Authority [IANA], [RFC2278] or start with X-
media-type specifies the media type (MIME content type) of the data that results from outputting the result tree; the charset parameter should not be specified explicitly; instead, when the top-level media type is text, a charset parameter should be added according to the character encoding actually used by the output method
doctype-system specifies the system identifier to be used in the document type declaration
doctype-public specifies the public identifier to be used in the document type declaration
omit-xml-declaration specifies whether the XSLT processor should output an XML declaration; the value must be yes or no
standalone specifies whether the XSLT processor should output a standalone document declaration; the value must be yes or no
cdata-section-elements specifies a list of the names of elements whose text node children should be output using CDATA sections

The detailed semantics of each attribute will be described separately for each output method for which it is applicable. If the semantics of an attribute are not described for an output method, then it is not applicable to that output method.

A stylesheet may contain multiple xsl:output elements and may include or import stylesheets that also contain xsl:output elements. All the xsl:output elements occurring in a stylesheet are merged into a single effective xsl:output element. For the cdata-section-elements attribute, the effective value is the union of the specified values. For other attributes, the effective value is the specified value with the highest import precedence. It is an error if there is more than one such value for an attribute. An XSLT processor may signal the error; if it does not signal the error, if should recover by using the value that occurs last in the stylesheet. 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.

16.1 XML Output Method

The xml output method outputs the result tree as a well-formed XML external general parsed entity. If the root node of the result tree has a single element node child and no text node children, then the entity should also be a well-formed XML document entity. When the entity is referenced within a trivial XML document wrapper like this


<?xml version="xml-version"?>
<!DOCTYPE doc [
<!ENTITY e SYSTEM "entity-URI">
]>
<doc>&e;</doc>

where entity-URI is a URI for the entity and xml-version corresponds to the XML version of the entity, then the wrapper document as a whole should be a well-formed XML document conforming to the XML Namespaces Recommendation [XML Names]. In addition, the output should be such that if a new tree was constructed by parsing the wrapper as an XML document as specified in [3 Data Model], and then removing the document element, making its children instead be children of the root node, then the new tree would be the same as the result tree, with the following possible exceptions:

The order of attribute and namespace nodes in the two trees may be different.
The new tree may contain namespace nodes that were not present in the result tree.

NOTE: An XSLT processor may need to add namespace declarations in the course of outputting the result tree as XML.
The base URIs of nodes in the two trees may be different.

If the XSLT processor generated a document type declaration because of the doctype-system attribute or generated a standalone document declaration because of the standalone attribute, then the output must be a well-formed XML document, and the above requirements apply to the tree constructed by parsing that document directly, without any wrapper, using an XML processor that does not process the DTD.

NOTE: Processing the DTD might cause additional attributes to appear in the tree because of attribute defaulting.

The version attribute specifies the version of XML to be used for outputting the result tree. If the XSLT processor does not support this version of XML, it should use a version of XML that it does support. The version output in the XML declaration (if an XML declaration is output) should correspond to the version of XML that the processor used for outputting the result tree. The default value is 1.0. If the value is 1.1 and the XSLT processor does support XML 1.1 and XML Names 1.1, then the following restrictions apply:

Undeclaring prefixes must not occur.
Unicode normalization must not occur.

The encoding attribute specifies the preferred encoding to use for outputting the result tree. XSLT processors are required to respect values of UTF-8 and UTF-16. For other values, if the XSLT processor does not support the specified encoding it may signal an error; if it does not signal an error it should use UTF-8 or UTF-16 instead. The XSLT processor must not use an encoding whose name does not match the EncName production of the XML Recommendation [XML] or [XML 1.1]. If no encoding attribute is specified, then the XSLT processor should use either UTF-8 or UTF-16. It is possible that the result tree will contain a character that cannot be represented in the encoding that the XSLT processor is using for output. In this case, if the character occurs in a context where XML recognizes character references (i.e. in the value of an attribute node or text node), then the character should be output as a character reference; otherwise (for example if the character occurs in the name of an element) the XSLT processor should signal an error.

If the indent attribute has the value yes, then the xml output method may output whitespace in addition to the whitespace in the result tree (possibly based on whitespace stripped from either the source document or the stylesheet) in order to indent the result nicely; if the indent attribute has the value no, it should not output any additional whitespace. The default value is no. The xml output method should use an algorithm to output additional whitespace that ensures that the result if whitespace were to be stripped from the output using the process described in [3.4 Whitespace Stripping] with the set of whitespace-preserving elements consisting of just xsl:text would be the same when additional whitespace is output as when additional whitespace is not output.

NOTE: It is usually not safe to use indent="yes" with document types that include element types with mixed content.

The cdata-section-elements attribute contains a whitespace-separated list of QNames. Each QName is expanded into an expanded-name using the namespace declarations in effect on the xsl:output element in which the QName occurs; if there is a default namespace, it is used for QNames that do not have a prefix. The expansion is performed before the merging of multiple xsl:output elements into a single effective xsl:output element. If the expanded-name of the parent of a text node is a member of the list, then the text node should be output as a CDATA section. For example,

<xsl:output cdata-section-elements="example"/>

would cause a literal result element written in the stylesheet as

<example>&lt;foo></example>

or as

<example><![CDATA[<foo>]]></example>

to be output as

<example><![CDATA[<foo>]]></example>

If the text node contains the sequence of characters ]]>, then the currently open CDATA section should be closed following the ]] and a new CDATA section opened before the >. For example, a literal result element written in the stylesheet as

<example>]]&gt;</example>

would be output as

<example><![CDATA[]]]]><![CDATA[>]]></example>

If the text node contains a character that is not representable in the character encoding being used to output the result tree, then the currently open CDATA section should be closed before the character, the character should be output using a character reference or entity reference, and a new CDATA section should be opened for any further characters in the text node.

CDATA sections should not be used except for text nodes that the cdata-section-elements attribute explicitly specifies should be output using CDATA sections.

The xml output method should output an XML declaration unless the omit-xml-declaration attribute has the value yes. The XML declaration should include both version information and an encoding declaration. If the standalone attribute is specified, it should include a standalone document declaration with the same value as the value as the value of the standalone attribute. Otherwise, it should not include a standalone document declaration; this ensures that it is both an XML declaration (allowed at the beginning of a document entity) and a text declaration (allowed at the beginning of an external general parsed entity).

If the doctype-system attribute is specified, the xml output method should output a document type declaration immediately before the first element. The name following <!DOCTYPE should be the name of the first element. If doctype-public attribute is also specified, then the xml output method should output PUBLIC followed by the public identifier and then the system identifier; otherwise, it should output SYSTEM followed by the system identifier. The internal subset should be empty. The doctype-public attribute should be ignored unless the doctype-system attribute is specified.

The media-type attribute is applicable for the xml output method. The default value for the media-type attribute is text/xml.

16.2 HTML Output Method

The html output method outputs the result tree as HTML; for example,

<xsl:stylesheet version="1.0"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:output method="html"/>

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

...

</xsl:stylesheet>

The version attribute indicates the version of the HTML. The default value is 4.0, which specifies that the result should be output as HTML conforming to the HTML 4.0 Recommendation [HTML].

The html output method should not output an element differently from the xml output method unless the expanded-name of the element has a null namespace URI; an element whose expanded-name has a non-null namespace URI should be output as XML. If the expanded-name of the element has a null namespace URI, but the local part of the expanded-name is not recognized as the name of an HTML element, the element should output in the same way as a non-empty, inline element such as span.

The html output method should not output an end-tag for empty elements. For HTML 4.0, the empty elements are area, base, basefont, br, col, frame, hr, img, input, isindex, link, meta and param. For example, an element written as <br/> or <br></br> in the stylesheet should be output as <br>.

The html output method should recognize the names of HTML elements regardless of case. For example, elements named br, BR or Br should all be recognized as the HTML br element and output without an end-tag.

The html output method should not perform escaping for the content of the script and style elements. For example, a literal result element written in the stylesheet as

<script>if (a &lt; b) foo()</script>

<script><![CDATA[if (a < b) foo()]]></script>

should be output as

<script>if (a < b) foo()</script>

The html output method should not escape < characters occurring in attribute values.

If the indent attribute has the value yes, then the html output method may add or remove whitespace as it outputs the result tree, so long as it does not change how an HTML user agent would render the output. The default value is yes.

The html output method should escape non-ASCII characters in URI attribute values using the method recommended in Section B.2.1 of the HTML 4.0 Recommendation.

The html output method may output a character using a character entity reference, if one is defined for it in the version of HTML that the output method is using.

The html output method should terminate processing instructions with > rather than ?>.

The html output method should output boolean attributes (that is attributes with only a single allowed value that is equal to the name of the attribute) in minimized form. For example, a start-tag written in the stylesheet as

<OPTION selected="selected">

should be output as

<OPTION selected>

The html output method should not escape a & character occurring in an attribute value immediately followed by a { character (see Section B.7.1 of the HTML 4.0 Recommendation). For example, a start-tag written in the stylesheet as

<BODY bgcolor='&amp;{{randomrbg}};'>

should be output as

<BODY bgcolor='&{randomrbg};'>

The encoding attribute specifies the preferred encoding to be used. If there is a HEAD element, then the html output method should add a META element immediately after the start-tag of the HEAD element specifying the character encoding actually used. For example,

<HEAD>
<META http-equiv="Content-Type" content="text/html; charset=EUC-JP">
...

It is possible that the result tree will contain a character that cannot be represented in the encoding that the XSLT processor is using for output. In this case, if the character occurs in a context where HTML recognizes character references, then the character should be output as a character entity reference or decimal numeric character reference; otherwise (for example, in a script or style element or in a comment), the XSLT processor should signal an error.

If the doctype-public or doctype-system attributes are specified, then the html output method should output a document type declaration immediately before the first element. The name following <!DOCTYPE should be HTML or html. If the doctype-public attribute is specified, then the output method should output PUBLIC followed by the specified public identifier; if the doctype-system attribute is also specified, it should also output the specified system identifier following the public identifier. If the doctype-system attribute is specified but the doctype-public attribute is not specified, then the output method should output SYSTEM followed by the specified system identifier.

The media-type attribute is applicable for the html output method. The default value is text/html.

16.3 Text Output Method

The text output method outputs the result tree by outputting the string-value of every text node in the result tree in document order without any escaping.

The media-type attribute is applicable for the text output method. The default value for the media-type attribute is text/plain.

The encoding attribute identifies the encoding that the text output method should use to convert sequences of characters to sequences of bytes. The default is system-dependent. If the result tree contains a character that cannot be represented in the encoding that the XSLT processor is using for output, the XSLT processor should signal an error.

16.4 Disabling Output Escaping

Normally, the xml output method escapes & and < (and possibly other characters) when outputting text nodes. This ensures that the output is well-formed XML. 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 provides a mechanism for disabling output escaping. 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 a text node generated by instantiating the xsl:value-of or xsl:text element should be output without any escaping. For example,

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

should generate the single character <.

It is an error for output escaping to be disabled for a text node that is used for 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; it is also an error to convert a result tree fragment to a number or a string if the result tree fragment contains a text node for which escaping was disabled. In both cases, an XSLT processor may signal the error; if it does not signal the error, it must recover by ignoring the disable-output-escaping attribute.

When a root node is copied using an xsl:copy-of element (see [11.3 Using Values of Variables and Parameters with xsl:copy-of]) and escaping was disabled for a text node descendant of that root node, then escaping should also be disabled for the resulting copy of that text node. For example

<xsl:variable name="x"> <xsl:text disable-output-escaping="yes"><</xsl:text> </xsl:variable> <xsl:copy-of select="$x"/>

should output < not <.

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.

An XSLT processor will only be able to disable output escaping if it controls how the result tree is output. This may not always be the case. For example, the result tree may be used as the source tree for another XSLT transformation instead of being output. An XSLT processor is not required to support disabling output escaping. If an xsl:value-of or xsl:text specifies that output escaping should be disabled and the XSLT processor does not support this, the XSLT processor may signal an error; if it does not signal an error, it must recover by not disabling output escaping.

If output escaping is disabled for a character that is not representable in the encoding that the XSLT processor is using for output, then the XSLT processor may signal an error; if it does not signal an error, it must recover by not disabling output escaping.

Since disabling output escaping may not work with all XSLT processors and can result in XML that is not well-formed, it should be used only when there is no alternative.

17 Conformance

A conforming XSLT processor must be able to use a stylesheet to transform a source tree into a result tree as specified in this document. A conforming XSLT processor need not be able to output the result in XML or in any other form.

NOTE: Vendors of XSLT processors are strongly encouraged to provide a way to verify that their processor is behaving conformingly by allowing the result tree to be output as XML or by providing access to the result tree through a standard API such as the DOM or SAX.

A conforming XSLT processor must signal any errors except for those that this document specifically allows an XSLT processor not to signal. A conforming XSLT processor may but need not recover from any errors that it signals.

A conforming XSLT processor may impose limits on the processing resources consumed by the processing of a stylesheet.

18 Notation

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. The meaning of syntax summary notation is as follows:

An attribute is required if and only if its name is in bold.
The string that occurs in the place of an attribute value specifies the allowed values of the attribute. If this is surrounded by curly braces, then the attribute value is treated as an attribute value template, and the string occurring within curly braces specifies the allowed values of the result of instantiating 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.
If the element is allowed not to be empty, then the element contains a comment specifying the allowed content. The allowed content is specified in a similar way to an element type declaration in XML; template means that any mixture of text nodes, literal result elements, extension elements, and XSLT elements from the instruction category is allowed; top-level-elements means that any mixture of XSLT elements from the top-level-element category is allowed.
The element is prefaced by comments indicating if it belongs to the instruction category or top-level-element category or both. The category of an element just affects whether it is allowed in the content of elements that allow a template or top-level-elements.

A References

A.1 Normative References

XML: World Wide Web Consortium. Extensible Markup Language (XML) 1.0. W3C Recommendation. See http://www.w3.org/TR/1998/REC-xml-19980210
XML Names: World Wide Web Consortium. Namespaces in XML. W3C Recommendation. See http://www.w3.org/TR/REC-xml-names
XPath: World Wide Web Consortium. XML Path Language. W3C Recommendation. See xpath
XML 1.1: World Wide Web Consortium. Extensible Markup Language (XML) 1.1. W3C Recommendation. See http://www.w3.org/TR/xml11/
XML Names 1.1: World Wide Web Consortium. Namespaces in XML 1.1. W3C Recommendation. See http://www.w3.org/TR/xml-names11/

A.2 Other References

CSS2: World Wide Web Consortium. Cascading Style Sheets, level 2 (CSS2). W3C Recommendation. See http://www.w3.org/TR/1998/REC-CSS2-19980512
DSSSL: International Organization for Standardization, International Electrotechnical Commission. ISO/IEC 10179:1996. Document Style Semantics and Specification Language (DSSSL). International Standard.
HTML: World Wide Web Consortium. HTML 4.0 specification. W3C Recommendation. See http://www.w3.org/TR/REC-html40
IANA: Internet Assigned Numbers Authority. Character Sets. See ftp://ftp.isi.edu/in-notes/iana/assignments/character-sets.
RFC2278: N. Freed, J. Postel. IANA Charset Registration Procedures. IETF RFC 2278. See http://www.ietf.org/rfc/rfc2278.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.
UNICODE TR10: Unicode Consortium. Unicode Technical Report #10. Unicode Collation Algorithm. Unicode Technical Report. See http://www.unicode.org/unicode/reports/tr10/index.html.
XHTML: World Wide Web Consortium. XHTML 1.0: The Extensible HyperText Markup Language. W3C Proposed Recommendation. See http://www.w3.org/TR/xhtml1
XPointer: World Wide Web Consortium. XML Pointer Language (XPointer). W3C Working Draft. See http://www.w3.org/TR/xptr
XML Stylesheet: World Wide Web Consortium. Associating stylesheets with XML documents. W3C Recommendation. See http://www.w3.org/TR/xml-stylesheet
XSL: World Wide Web Consortium. Extensible Stylesheet Language (XSL). W3C Working Draft. See http://www.w3.org/TR/WD-xsl

B Element Syntax Summary