I am wanting to capture each portion (denoted with parenthesis) of the following string, where each of the portions are optional. Possible strings could be:

4Y6M12D
4Y12D
6M

Where

$year = '4Y'
$month = '6M'
$day = '12D'

I thought I could use:
<xsl:analyze-string select="'4Y6M12D'" regex="(\d{1,2}Y)(\d{1,2}M)(\d{1,2}D)">

<xsl:matching-substring>
<xsl:variable name="year" select="regex-group(1)"/>
<xsl:variable name="month" select="regex-group(2)"/>
<xsl:variable name="day" select="regex-group(3)"/>
</xsl:matching-substring>

</xsl:analyze-string>

Is there a better way to capture these variables. I know I can use matches() to return a boolean, but is there an equivalent that will return just that portion of the string that matches the regex.

somefunction('4Y12D','(\d{1,2}Y)') returns 4Y

The regex attribute of xsl:analyze-string is an attribute value template, so curly braces need to be doubled. Alternatively put the regex in a variable:

<xsl:variable name="regex">(\d{1,2}Y)(\d{1,2}M)(\d{1,2}D)</xsl:variable>
<xsl:analyze-string select="'4Y6M12D'" regex="{$regex}">

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