I don't see the necessity for reversing the content. True, "greedy" matching
(implying backup) may not be the fastest way in some situations; as an
alternative there is "reluctant" matching (e.g. '.*?').

But if the YYY is a literal string (not a pattern) substring-before is
suffcient.

  <out1>
    <xsl:variable name="bef" select="substring-before(.,'YYY')"/>
    <xsl:value-of select="substring($bef,string-length($bef)-400+1,400)"/>
  </out1>

If there's the possibility that there aren't 400 characters before YYY,
add a choice.

Here is the solution with pattern matching:
  <out2>
    <xsl:variable name="bef" select="."/>
    <xsl:value-of select="replace($bef,'^.*?(.{400})YYY.*$', '$1')"/>
  </out2>
Here, using '.{1,400}' would be necessary to handle "short" cases.

-W



On 13 June 2010 10:11, Alex Muir <alex.g.muir@xxxxxxxxx> wrote:
>
> Hi,
>
> I need to select 400 characters before a string such as YYY in a
> larger text document.
>
> I've in the past reversed the content to then find the 400 characters
> before YYY using regex effectively however I'm wondering if there is a
> better perhaps simpler way to do this in xslt?
>
>
> Thanks
>
>
> --
> Alex
>
> An informal recording with one mic under a tree leads to some pretty
> sweet acoustic sounds.
> https://sites.google.com/site/greigconteh/albums/diabarte-and-sons