Table of contents

Appendices

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.

Stylesheet Inclusion[top]

< include
   href= uri-reference >
   <-- Content: -->
< /include>

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 [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 [Literal Result Element as Stylesheet]. The included stylesheet is treated the same as the equivalent xsl:stylesheet element.

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

NOTE: 

Including a stylesheet multiple times can cause errors because of duplicate definitions. Such multiple inclusions are less obvious when they are indirect. For example, if stylesheet B includes stylesheet A, stylesheet C includes stylesheet A, and stylesheet D includes both stylesheet B and stylesheet C, then A will be included indirectly by D twice. If all of B, C and D are used as independent stylesheets, then the error can be avoided by separating everything in B other than the inclusion of A into a separate stylesheet B' and changing B to contain just inclusions of B' and A, similarly for C, and then changing D to include A, B', C'.

Stylesheet Import[top]

< import
   href= uri-reference >
   <-- Content: -->
< /import>

An XSLT stylesheet may import another XSLT stylesheet using an xsl:import element. Importing a stylesheet is the same as including it (see [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 [Base URI]).

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

For example,

<xsl:stylesheet version="1.0"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:import href="article.xsl"/>
  <xsl:import href="bigfont.xsl"/>
  <xsl:attribute-set name="note-style">
    <xsl:attribute name="font-style">italic</xsl:attribute>
  </xsl:attribute-set>
</xsl:stylesheet>

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

For example, suppose

• stylesheet A imports stylesheets B and C in that order;

• stylesheet B imports stylesheet D;

• stylesheet C imports stylesheet E.

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

NOTE: 

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

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

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

NOTE: 

If xsl:apply-imports is used (see [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.