XPath Filters

XPath filters can match nodes matching a constraint expression, for example only matching sections with titles. In the following example, sections with titles are formatted differently than sections without titles. Using XPath filters, the stylesheet can use different templates to specify the formatting without using xsl:if.

default.xsl

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

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

<xsl:template match="section[@title]">
  <h1>
      <xsl:value-of select="@title"/>
  </h1>
  <xsl:apply-templates/>
</xsl:template>

A node may match more than one pattern. The full set of XSLT rules to tell which pattern to use are fairly involved, but if the stylesheet always puts general patterns first and specific patterns last, the XSLT engine will select the later pattern. In the above example, the filtered pattern "section[@title]" will match because it's more specific than "section". Even if the two patterns were equally specific, the engine would select "section[@title]" because it's later in the stylesheet.

hello.xtp
<section title="First Section"> Some text </section> <section> Section with no title </section>

<h1>First Section</h1> Some text Section with no title

StyleScript

The StyleScript translation is straightforward. The stylesheet just uses two templates, one with the filter pattern. Because StyleScript expands to XSL, the priority rules are exactly the same.

default.xsl
$template(section) << $apply-templates(); >> $template(section[@title]) << <h1>$(@title)</h1> $apply-templates(); >>

Summary

The XPath pattern a[b] selects a only if b exists.