XSLT, 2nd Edition

Back-references

A back-reference allows you to refer to a previously matched subexpression within the regular expression itself. As an example, say you want to find words that begin and end with the same two letters. The expression ([a-z]{2})(.*)\1 does the trick. The \1 represents whatever two characters matched the first subexpression. The back-reference \2 represents the match for the second subexpression, \3 represents the match for the third subexpression, and so on. (Notice that although the references go backwards, counting subexpressions goes from left to right.)

Here’s a sample stylesheet:

<?xml version="1.0" encoding="utf-8"?>
<!-- back-reference.xsl -->
<xsl:stylesheet version="2.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

  <xsl:output method="text"/>

  <xsl:template match="/">
    <xsl:text>Using back-references to find words that begin &#xA;</xsl:text>
    <xsl:text>  and end with the same two letters:&#xA;&#xA;</xsl:text>
    <xsl:text>  replace($x, '([a-z]{2})(.*)\1', '$1--$2--$1')&#xA;</xsl:text>
    <xsl:text>    edited:    </xsl:text>
    <xsl:value-of 
      select="replace('edited', '([a-z]{2})(.*)\1', '$1--$2--$1')"/>
    <xsl:text>&#xA;    editor:    </xsl:text>
    <xsl:value-of 
      select="replace('editor', '([a-z]{2})(.*)\1', '$1--$2--$1')"/>
    <xsl:text>&#xA;    educated:  </xsl:text>
    <xsl:value-of 
      select="replace('educated', '([a-z]{2})(.*)\1', '$1--$2--$1')"/>
    <xsl:text>&#xA;    orator:    </xsl:text>
    <xsl:value-of 
      select="replace('orator', '([a-z]{2})(.*)\1', '$1--$2--$1')"/> </xsl:template> </xsl:stylesheet> ...