Is there a better/more efficient way to convert:

Projects\Documents (...regex...)
TO
Projects\\Documents (...regex...)


<xsl:template name="escape_backslash">
  <xsl:param name="in"/>
  <xsl:param name="out"/>
  <xsl:choose>
    <xsl:when test="contains($in, '\')">
      <xsl:call-template name="escape_backslash">
        <xsl:with-param name="in" select="substring-after($in, '\')"/>
        <xsl:with-param name="out" select="concat($out, substring-before($in, '\'), '\\')"/>
      </xsl:call-template>
     </xsl:when>
     <xsl:otherwise>
       <xsl:value-of select="concat($out, $in)"/>
     </xsl:otherwise>
   </xsl:choose>
</xsl:template>

Unless you move to XSLT 2.0, you're stuck with this kind of approach.

Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference

Sorry, should rephrased question. Is there a more efficient way to do this in XSLT 2.0? I am using Saxon8.

In XSLT 2.0 it's

replace($in, '\\', '\\\\')

(in both the regex and the replacement string, a backslash is written as '\\')

Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference

Does it cost additional processing time if I defined it as a function and call it?

pc:escapeBackslash($path)

<xsl:function name="pc:escapeBackslash">
<xsl:param name="$in"/>
<xsl:sequence select="replace($in, '\\', '\\\\')"/>
</xsl:function>

Depends on your processor. Measure it and see. With a good optimizer, functions like that are likely to generate inline code.

Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference