XSL Transformations (XSLT)
XSL Transformations (XSLT)
Version 1.0
W3C Recommendation 16 November 1999
Status Update (6 April 2021):
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. Readers interested in richer versions of the XSLT specification are encouraged to refer to
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or
HTML
Latest version:
Previous versions:
Editor:
James Clark
W3C
MIT
INRIA
Keio
), All Rights Reserved. W3C
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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
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
A list of current W3C Recommendations and other technical documents can be
found at
This specification has been produced as part of the
W3C Style activity
Table of contents
Introduction
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
Data Model
3.1
Root Node
Children
3.2
Base URI
3.3
Unparsed
Entities
3.4
Whitespace Stripping
Expressions
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
Named Templates
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
Repetition
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
References
A.1
Normative
References
A.2
Other
References
Element Syntax Summary
DTD Fragment for XSLT Stylesheets
(Non-Normative)
Examples
(Non-Normative)
D.1
Document
Example
D.2
Data Example
Acknowledgements
(Non-Normative)
Changes from
Proposed Recommendation
(Non-Normative)
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]
, which may include both
elements that are defined by XSLT and elements that are not defined by XSLT.
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
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
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 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
id
extension-element-prefixes =
tokens
exclude-result-prefixes =
tokens
version
number
id
extension-element-prefixes =
tokens
exclude-result-prefixes =
tokens
version
number
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.
...
...
...
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
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns="http://www.w3.org/TR/xhtml1/strict">
Total Amount:
has the same meaning as
xmlns="http://www.w3.org/TR/xhtml1/strict">
Total Amount:
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
, or it is a literal result element that does not have an
xsl:version
attribute and that is the document element of a
stylesheet using the simplified syntax (see
2.3 Literal Result Element as
Stylesheet
). 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:
Sorry, this stylesheet requires XSLT 1.1.
NOTE:
If a stylesheet depends crucially on a top-level element
introduced by a version of XSL 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 XSL will not silently ignore the top-level
element. For example,
...
...
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
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
includes
stylesheet
, stylesheet
includes stylesheet
, and stylesheet
includes both stylesheet
and stylesheet
, then
will be
included indirectly by
twice. If all of
and
are used as independent stylesheets, then the
error can be avoided by separating everything in
other than
the inclusion of
into a separate stylesheet
B'
and
changing
to contain just inclusions of
B'
and
, similarly for
, and then changing
to
include
B'
C'
2.6.2 Stylesheet Import
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,
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
imports stylesheets
and
in that order;
stylesheet
imports stylesheet
stylesheet
imports stylesheet
Then the order of import precedence (lowest first) is
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:
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:fo="http://www.w3.org/1999/XSL/Format">
...
NOTE:
A stylesheet that is embedded in the document to which it is to
be applied or that may be included or imported into an 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
tokens
/>
tokens
/>
For source documents, the set of whitespace-preserving element names is
specified by
xsl:strip-space
and
xsl:preserve-space
top-level
elements. These elements each have an
elements
attribute whose value is a whitespace-separated list of
NameTest
s. Initially,
the set of whitespace-preserving element names contains all element names. If
an element name matches a
NameTest
in an
xsl:strip-space
element, then it is removed from the set of
whitespace-preserving element names. If an element name matches a
NameTest
in an
xsl:preserve-space
element, then it is added to the set of
whitespace-preserving element names. An element matches a
NameTest
if and only if the
NameTest
would be true
for the element as an
XPath
node test
. Conflicts between matches to
xsl:strip-space
and
xsl:preserve-space
elements are resolved the same way as
conflicts between template rules (see
5.5 Conflict
Resolution for Template Rules
). Thus, the applicable match for a
particular element name is determined as follows:
First, any match with lower
import
precedence
than another match is ignored.
Next, any match with a
NameTest
that has a
lower
default priority
than the
default priority
of the
NameTest
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.
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 template
s.
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
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 a
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
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,
matches any
element, because
for any
if the expression
is evaluated with the
parent of the
element as context the resulting node-set will
contain that
element as one of its members.
NOTE:
This matches even a
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
StepPattern
s 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
pattern
name =
qname
priority =
number
mode =
qname
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
The following template rule matches
emph
elements and
produces a
fo:inline-sequence
formatting object with a
font-weight
property of
bold
NOTE:
Examples in this document use the
fo:
prefix for
the namespace
, 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
node-set-expression
mode =
qname
This example creates a block for a
chapter
element and then
processes its immediate children.
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.
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
The following example processes all of the
given-name
s of the
author
s that are children of
author-group
This example processes all of the
heading
descendant elements
of the
book
element.
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
Employee
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.
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
the rule
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,
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
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:
Another stylesheet could import
doc.xsl
and modify the
treatment of
example
elements as follows:
The combined effect would be to transform an
example
into an
element of the form:
...
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:
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
There is also a built-in template rule for text and attribute nodes that
copies text through:
The built-in template rule for processing instructions and comments is to
do nothing.
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
qname
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
), 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
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
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">
will generate an XSLT stylesheet from a document of the form:
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
= {
qname
namespace = {
uri-reference
use-attribute-sets =
qnames
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 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
= {
qname
namespace = {
uri-reference
}>
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:
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.
NOTE:
When an
xsl:attribute
contains a text node with a
newline, then the XML output must contain a character reference. For
example,
y
will result in the output
a="x
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
qname
use-attribute-sets =
qnames
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.
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.
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
).
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
= {
ncname
}>
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
would create the processing instruction
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
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
would create the comment
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
qnames
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:
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
).
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:
then it can simply do
instead of
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
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.
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.
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.
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:
With this source
the result would be
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:
is
not
allowed. Instead, use simply:
7.7 Numbering
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.
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:
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 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:
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.
format="1.1 "/>
format="A.1 "/>
The following example numbers notes sequentially within a chapter:
The following example would number
H4
elements in HTML with a
three-part label:
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
. 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
th format token will be used to format
the
th 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
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
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
generates the sequence
A B C ...
Z AA AB AC...
A format token
generates the sequence
a b c ...
z aa ab ac...
A format token
generates the sequence
i ii iii
iv v vi vii viii ix x ...
A format token
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
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
and
. 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
node-set-expression
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
the following would create an HTML document containing a table with a row
for each
customer
element
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
boolean-expression
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:
The following colors every other table row yellow:
9.2
Conditional Processing with
xsl:choose
boolean-expression
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.
10 Sorting
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
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 unsorted 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
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 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
with
case-order="upper-first"
and
a A b B
are
sorted with
case-order="lower-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
...
Then a list of employees sorted by name could be generated using:
11 Variables and Parameters
qname
select =
expression
qname
select =
expression
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; within this region, any
binding of the variable that was visible on the variable-binding element
itself is hidden. Thus, only the innermost binding of a variable 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
select
attribute, then the value of the variable is an
empty string. Thus
is equivalent to
NOTE:
When a variable is used to select nodes by position, be careful
not to do:
...
This will output the value of the first item element, because the variable
will be bound to a result tree fragment, not a number.
Instead, do either
...
or
...
NOTE:
One convenient way to specify the empty node-set as the default
value of a parameter is:
11.3 Using Values of Variables and Parameters with
xsl:copy-of
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.
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. 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. 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
references a global variable
, then the value for
must be computed before the value of
. 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.
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 all
following siblings and their descendants. 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 all following siblings and their descendants. 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. Thus, the following is an
error:
However, the following is allowed:
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,
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
qname
select =
expression
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
. 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
to a template that does not have an
xsl:param
element for
; 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.
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 is
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. 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
, name
and value
, we say that node
has a key with name
and value
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.
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
has a key with name
and value
if and only if there is an
xsl:key
element such
that:
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
; and
when the expression specified in the
use
attribute of
the
xsl:key
element is evaluated with
as the
current node and with a node list containing just
as the
current node list resulting in an object
, then either
is equal to the result of converting
to a
string as if by a call to the
string
function, or
is a node-set and
is equal to the
string-value of one or more of the nodes in
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
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
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:
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
and a
function
element to refer to function names
Then the stylesheet could generate hyperlinks between the references and
definitions as follows:
The
key
can be used to retrieve a key
from a document other than the document containing the context node. For
example, suppose a document contains bibliographic references in the form
, and there is a separate XML
document
bib.xml
containing a bibliographic database with
entries in the form:
Then the stylesheet could use the following to transform the
bibref
elements:
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.
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).
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 (
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,
means the same as
However, within square brackets the current node is usually different from
the context node. For example,
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
which means the same as
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.
13 Messages
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
are stored in an XML file
resources/
.xml
in the form:
Then a stylesheet could use the following approach to localize
messages:
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 namespace
s. 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
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. 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
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
entity-URI
">
]>
where
entity-URI
is a URI for 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 attributes 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.
If the XSLT processor generated a document type declaration because of the
doctype-system
attribute, then the above requirements apply to
the entity with the generated document type declaration removed.
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 value of the
version
attribute
should match the
VersionNum
production
of the XML Recommendation
[XML]
. The default value is
1.0
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]
. 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
QName
s. 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
QName
s 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,
would cause a literal result element written in the stylesheet as
or as
to be output as
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
would be output as
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 a 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
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,
...
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
or
in the
stylesheet should be output as
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
or
should be output as
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
%char-instructions;
| xsl:processing-instruction
| xsl:comment
| xsl:element
| xsl:attribute
">
(#PCDATA
%char-instructions;)*
">
(#PCDATA
%instructions;
%result-elements;)*
">
(xsl:import*,
(xsl:include
| xsl:strip-space
| xsl:preserve-space
| xsl:output
| xsl:key
| xsl:decimal-format
| xsl:attribute-set
| xsl:variable
| xsl:param
| xsl:template
| xsl:namespace-alias
%non-xsl-top-level;)*)
">
extension-element-prefixes CDATA #IMPLIED
exclude-result-prefixes CDATA #IMPLIED
id ID #IMPLIED
version NMTOKEN #REQUIRED
xmlns:xsl CDATA #FIXED "http://www.w3.org/1999/XSL/Transform"
%space-att;
'>
xsl:extension-element-prefixes CDATA #IMPLIED
xsl:exclude-result-prefixes CDATA #IMPLIED
xsl:use-attribute-sets %qnames; #IMPLIED
xsl:version NMTOKEN #IMPLIED
'>
method %qname; #IMPLIED
version NMTOKEN #IMPLIED
encoding CDATA #IMPLIED
omit-xml-declaration (yes|no) #IMPLIED
standalone (yes|no) #IMPLIED
doctype-public CDATA #IMPLIED
doctype-system CDATA #IMPLIED
cdata-section-elements %qnames; #IMPLIED
indent (yes|no) #IMPLIED
media-type CDATA #IMPLIED
name %qname; #REQUIRED
match %pattern; #REQUIRED
use %expr; #REQUIRED
name %qname; #IMPLIED
decimal-separator %char; "."
grouping-separator %char; ","
infinity CDATA "Infinity"
minus-sign %char; "-"
NaN CDATA "NaN"
percent %char; "%"
per-mille %char; "‰"
zero-digit %char; "0"
digit %char; "#"
pattern-separator %char; ";"
stylesheet-prefix CDATA #REQUIRED
result-prefix CDATA #REQUIRED
(#PCDATA
%instructions;
%result-elements;
| xsl:param)*
match %pattern; #IMPLIED
name %qname; #IMPLIED
priority %priority; #IMPLIED
mode %qname; #IMPLIED
%space-att;
select %expr; #REQUIRED
disable-output-escaping (yes|no) "no"
level (single|multiple|any) "single"
count %pattern; #IMPLIED
from %pattern; #IMPLIED
value %expr; #IMPLIED
format %avt; '1'
lang %avt; #IMPLIED
letter-value %avt; #IMPLIED
grouping-separator %avt; #IMPLIED
grouping-size %avt; #IMPLIED
select %expr; "node()"
mode %qname; #IMPLIED
(#PCDATA
%instructions;
%result-elements;
| xsl:sort)*
select %expr; #REQUIRED
%space-att;
select %expr; "."
lang %avt; #IMPLIED
data-type %avt; "text"
order %avt; "ascending"
case-order %avt; #IMPLIED
test %expr; #REQUIRED
%space-att;
test %expr; #REQUIRED
%space-att;
name %qname; #REQUIRED
use-attribute-sets %qnames; #IMPLIED
name %qname; #REQUIRED
name %qname; #REQUIRED
select %expr; #IMPLIED
name %qname; #REQUIRED
select %expr; #IMPLIED
name %qname; #REQUIRED
select %expr; #IMPLIED
disable-output-escaping (yes|no) "no"
name %avt; #REQUIRED
%space-att;
name %avt; #REQUIRED
namespace %avt; #IMPLIED
use-attribute-sets %qnames; #IMPLIED
%space-att;
name %avt; #REQUIRED
namespace %avt; #IMPLIED
%space-att;
%space-att;
use-attribute-sets %qnames; #IMPLIED
%space-att;
terminate (yes|no) "no"
D Examples (Non-Normative)
D.1 Document Example
This example is a stylesheet for transforming documents that conform to a
simple DTD into XHTML
[XHTML]
. The DTD is:
The stylesheet is:
xmlns="http://www.w3.org/TR/xhtml1/strict">
indent="yes"
encoding="iso-8859-1"
/>
NOTE:
With the following input document
it would produce the following result
Document Title
Chapter Title
Section Title
This is a test.
NOTE: This is a note.
Another Section Title
This is another test.
NOTE: This is another note.
D.2 Data Example
This is an example of transforming some data represented in XML using
three different XSLT stylesheets to produce three different representations
of the data, HTML, SVG and VRML.
The input data is:
The following stylesheet, which uses the simplified syntax described in
2.3 Literal Result Element as
Stylesheet
, transforms the data into HTML:
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
lang="en">
| Division | Revenue | Growth | Bonus |
|---|---|---|---|
The HTML output is:
| Division | Revenue | Growth | Bonus |
|---|---|---|---|
| North | 10 | 9 | 7 |
| West | 6 | -1.5 | 2 |
| South | 4 | 3 | 4 |
The following stylesheet transforms the data into SVG:
xmlns="http://www.w3.org/Graphics/SVG/SVG-19990812.dtd">
The SVG output is:
The following stylesheet transforms the data into VRML:
# externproto definition of a single bar element
EXTERNPROTO bar [
field SFInt32 x
field SFInt32 y
field SFInt32 z
field SFString name
"http://www.vrml.org/WorkingGroups/dbwork/barProto.wrl"
# inline containing the graph axes
Inline {
url "http://www.vrml.org/WorkingGroups/dbwork/barAxes.wrl"
bar {
x
y
z
name "
The VRML output is:
#VRML V2.0 utf8
# externproto definition of a single bar element
EXTERNPROTO bar [
field SFInt32 x
field SFInt32 y
field SFInt32 z
field SFString name
"http://www.vrml.org/WorkingGroups/dbwork/barProto.wrl"
# inline containing the graph axes
Inline {
url "http://www.vrml.org/WorkingGroups/dbwork/barAxes.wrl"
bar {
x 10
y 9
z 7
name "North"
bar {
x 4
y 3
z 4
name "South"
bar {
x 6
y -1.5
z 2
name "West"
E Acknowledgements
(Non-Normative)
The following have contributed to authoring this draft:
Daniel Lipkin, Saba
Jonathan Marsh, Microsoft
Henry Thompson, University of Edinburgh
Norman Walsh, Arbortext
Steve Zilles, Adobe
This specification was developed and approved for publication by the W3C
XSL Working Group (WG). WG approval of this specification does not
necessarily imply that all WG members voted for its approval. The current
members of the XSL WG are:
Sharon Adler, IBM (Co-Chair); Anders Berglund, IBM; Perin Blanchard, Novell;
Scott Boag, Lotus; Larry Cable, Sun; Jeff Caruso, Bitstream; James Clark;
Peter Danielsen, Bell Labs; Don Day, IBM; Stephen Deach, Adobe; Dwayne Dicks,
SoftQuad; Andrew Greene, Bitstream; Paul Grosso, Arbortext; Eduardo Gutentag,
Sun; Juliane Harbarth, Software AG; Mickey Kimchi, Enigma; Chris Lilley, W3C;
Chris Maden, Exemplary Technologies; Jonathan Marsh, Microsoft; Alex
Milowski, Lexica; Steve Muench, Oracle; Scott Parnell, Xerox; Vincent Quint,
W3C; Dan Rapp, Novell; Gregg Reynolds, Datalogics; Jonathan Robie, Software
AG; Mark Scardina, Oracle; Henry Thompson, University of Edinburgh; Philip
Wadler, Bell Labs; Norman Walsh, Arbortext; Sanjiva Weerawarana, IBM; Steve
Zilles, Adobe (Co-Chair)
F Changes from
Proposed Recommendation (Non-Normative)
The following are the changes since the Proposed Recommendation:
The
xsl:version
attribute is required on a literal
result element used as a stylesheet (see
2.3 Literal Result Element as
Stylesheet
).
The
data-type
attribute on
xsl:sort
can
use a prefixed name to specify a data-type not defined by XSLT (see
10 Sorting
).
Features under Consideration for Future Versions of XSLT (Non-Normative)
The following features are under consideration for versions of XSLT after
XSLT 1.0:
a conditional expression;
support for XML Schema datatypes and archetypes;
support for something like style rules in the original XSL
submission;
an attribute to control the default namespace for names occurring in
XSLT attributes;
support for entity references;
support for DTDs in the data model;
support for notations in the data model;
a way to get back from an element to the elements that reference it
(e.g. by IDREF attributes);
an easier way to get an ID or key in another document;
support for regular expressions for matching against any or all of
text nodes, attribute values, attribute names, element type names;
case-insensitive comparisons;
normalization of strings before comparison, for example for
compatibility characters;
a function
string resolve(node-set)
function that
treats the value of the argument as a relative URI and turns it into an
absolute URI using the base URI of the node;
multiple result documents;
defaulting the
select
attribute on
xsl:value-of
to the current node;
an attribute on
xsl:attribute
to control how the
attribute value is normalized;
additional attributes on
xsl:sort
to provide further
control over sorting, such as relative order of scripts;
a way to put the text of a resource identified by a URI into the
result tree;
allow unions in steps (e.g.
foo/(bar|baz)
);
allow for result tree fragments all operations that are allowed for
node-sets;
a way to group together consecutive nodes having duplicate
subelements or attributes;
features to make handling of the HTML
style
attribute
more convenient.