Table of contents

Appendices

7.1 Creating Elements and Attributes

Literal Result Elements[top]

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

The created element node will also have a copy of the namespace nodes that were present on the element node in the stylesheet tree with the exception of any namespace node whose string-value is the XSLT namespace URI (http://www.w3.org/1999/XSL/Transform), a namespace URI declared as an extension namespace (see [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

< namespace-alias
   stylesheet-prefix= prefix
   result-prefix= prefix >
   <-- Content: -->
< /namespace-alias>

A stylesheet can use the xsl:namespace-alias element to declare that one namespace URI is an alias for another namespace URI. When a Literal Namespace URI has been declared to be an alias for another namespace URI, then the namespace URI in the result tree will be the namespace URI that the literal namespace URI is an alias for, instead of the literal namespace URI itself. The xsl:namespace-alias element declares that the namespace URI bound to the prefix specified by the stylesheet-prefix attribute is an alias for the namespace URI bound to the prefix specified by the result-prefix attribute. Thus, the stylesheet-prefix attribute specifies the namespace URI that will appear in the stylesheet, and the result-prefix attribute specifies the corresponding namespace URI that will appear in the result tree. The default namespace (as declared by xmlns) may be specified by using #default instead of a prefix. If a namespace URI is declared to be an alias for multiple different namespace URIs, then the declaration with the highest Import Precedence is used. It is an error if there is more than one such declaration. An XSLT processor may signal the error; if it does not signal the error, it must recover by choosing, from amongst the declarations with the highest import precedence, the one that occurs last in the stylesheet.

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

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

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

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

<xsl:template match="block">
  <axsl:template match="{.}">
     <fo:block><axsl:apply-templates/></fo:block>
  </axsl:template>
</xsl:template>

</xsl:stylesheet>

will generate an XSLT stylesheet from a document of the form:

<elements>
<block>p</block>
<block>h1</block>
<block>h2</block>
<block>h3</block>
<block>h4</block>
</elements>

NOTE: 

It may be necessary also to use aliases for namespaces other than the XSLT namespace URI. For example, literal result elements belonging to a namespace dealing with digital signatures might cause XSLT stylesheets to be mishandled by general-purpose security software; using an alias for the namespace would avoid the possibility of such mishandling.

Creating Elements with xsl:element[top]

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

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

The name attribute is interpreted as an Attribute Value Template. It is an error if the string that results from instantiating the attribute value template is not a QName. An XSLT processor may signal the error; if it does not signal the error, then it must recover by making the 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.

Creating Attributes with xsl:attribute[top]

< attribute
   name= { qname }
   namespace= { uri-reference } >
   <-- Content: -->
< /attribute>

The xsl:attribute element can be used to add attributes to result elements whether created by literal result elements in the stylesheet or by instructions such as xsl:element. The expanded-name of the attribute to be created is specified by a required name attribute and an optional namespace attribute. Instantiating an xsl:attribute element adds an attribute node to the containing result element node. The content of the xsl:attribute element is a template for the value of the created attribute.

The name attribute is interpreted as an Attribute Value Template. It is an error if the string that results from instantiating the attribute value template is not a QName or is the string xmlns. An XSLT processor may signal the error; if it does not signal the error, it must recover by not adding the attribute to the result tree. If the namespace attribute is not present, then the QName is expanded into an expanded-name using the namespace declarations in effect for the xsl:attribute element, not including any default namespace declaration.

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

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

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

it will not result in a namespace declaration being output.

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

The following are all errors:

• Adding an attribute to an element after children have been added to it; implementations may either signal the error or ignore the attribute.

• Adding an attribute to a node that is not an element; implementations may either signal the error or ignore the attribute.

• Creating nodes other than text nodes during the instantiation of the content of the xsl:attribute element; implementations may either signal the error or ignore the offending nodes.

NOTE: 

When an xsl:attribute contains a text node with a newline, then the XML output must contain a character reference. For example,

<xsl:attribute name="a">x
y</xsl:attribute>

will result in the output

a="x
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.

Named Attribute Sets[top]

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

The xsl:attribute-set element defines a named set of attributes. The name attribute specifies the name of the attribute set. The value of the name attribute is a QName, which is expanded as described in [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 [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 [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 [Variables and Parameters]); thus, only variables and parameters declared by Top-level xsl:variable and xsl:param elements are visible.

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

<xsl:template match="chapter/heading">
  <fo:block quadding="start" xsl:use-attribute-sets="title-style">
    <xsl:apply-templates/>
  </fo:block>
</xsl:template>

<xsl:attribute-set name="title-style">
  <xsl:attribute name="font-size">12pt</xsl:attribute>
  <xsl:attribute name="font-weight">bold</xsl:attribute>
</xsl:attribute-set>

Multiple definitions of an attribute set with the same expanded-name are merged. An attribute from a definition that has higher Import Precedence takes precedence over an attribute from a definition that has lower Import Precedence. It is an error if there are two attribute sets that have the same expanded-name and equal import precedence and that both contain the same attribute, unless there is a definition of the attribute set with higher Import Precedence that also contains the attribute. An XSLT processor may signal the error; if it does not signal the error, it must recover by choosing from amongst the definitions that specify the attribute that have the highest import precedence the one that was specified last in the stylesheet. Where the attributes in an attribute set were specified is relevant only in merging the attributes into the attribute set; it makes no difference when the attribute set is used.