XSLT 2.0 regular expression replace - regex

Question

I have the following XML:
<t>a_35345_0_234_345_666_888</t>
I would like to replace the first occurrence of number after "_" with a fixed number 234. So the result should look like:
<t>a_234_0_234_345_666_888</t>
I have tried using the following but it does not work:
<xsl:stylesheet version="2.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xsl:template match="/">
<xsl:value-of select='replace(., "(.*)_\d+_(.*)", "$1_234_$2")'/>
</xsl:template>
</xsl:stylesheet>
UPDATE
The following works for me (thanks #Chris85). Just remove the underscore and add "? to make it non greedy.
<xsl:stylesheet version="2.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xsl:template match="/">
<xsl:value-of select='replace(., "(.*?)_\d+(.*)", "$1_234$2")'/>
</xsl:template>
</xsl:stylesheet>

Answer 1

Your regex is/was greedy, the .* consumes everything until the last occurrence of the next character.
So
(.*)_\d+_(.*)
was putting
a_35345_0_234_345_666_
into $1. Then 888 was being removed and nothing went into $2.
To make it non-greedy add a ? after the .*. This tells the * to stop at the first occurrence of the next character.
Functional example:
<xsl:stylesheet version="2.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xsl:template match="/">
<xsl:value-of select='replace(., "(.*?)_\d+(.*)", "$1_234$2")'/>
</xsl:template>
</xsl:stylesheet>
Here's some more documentation on repetition and greediness, http://www.regular-expressions.info/repeat.html.