2012-07-14

Matching Classes In XSLT

A while ago (well 2 years) I posted an entry about the differences between CSS selectors and Xpath expressions. An simple ".classname" in CSS is a noisy "contains(concat(' ', normalize-space(@class), ' '), ' first ')" in Xpath.

In XSLT this adds a lot of overhead. But if your XSLT processor supports EXSLT you are able to encapsulate it into a function.

I put this into a file "contains-token.xsl".


<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet
  version="1.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:func="http://exslt.org/functions"
  extension-element-prefixes="func"
>
<func:function name="func:contains-token">
  <xsl:param name="haystack">
  <xsl:param name="needle">
  <xsl:variable name="normalizedHaystack" select="concat(' ', normalize-space($haystack), ' ')"/>
  <xsl:variable name="normalizedNeedle" select="concat(' ', normalize-space($needle), ' ')"/>
  <func:result select="$needle != '' and contains($haystack, $needle)"/>
</func:function>

</xsl:stylesheet>


You need to declare the func namespace and define it as an extension prefix. The function definition is not unlike an normal template definition. You just have to use the "func:function" and "func:result" elements. Function always need to be inside an namespace. If in doubt, just use the "func" namespace itself.

In this case I normalize both parameters first and just validate if the haystack contains the needle.

Now it is possible to import the function and use it.


...
<xsl:import href="../functions/contains-token.xsl"/>

<xsl:template match="/">
  ...
  <xsl:value-of select=".//div[func:contains-token(@class, 'classname')]"/>
  ...
</xsl:template>
...


It is still longer then the CSS version but it is a lot more readable.