Extracting a number from a string in a XSLT file - regex

Question

Is there a way to extract a number from a string after a set of characters.
Our software uses XSLT files to convert emails into XML files. In the Subject line of an email there can be a reference to an already opened Incident/Service Request/Task.
For example - the Subject of an email could be:
RE: SR#51417: D_SATTER-NOV60LKA-I_G-A0201244
I want to extract the Service Request Number 51417 from the Subject.
The number will always be after the String "SR#". "SR#" could be written as "sr#", "Sr#" or "sR#".
I was trying to use the RegEx functions in XSLT but can't get it to work.
Do you have any suggestions on how to do this?
Thanks in advance.
Update
I am trying the solution provided by cyclexx. This is the Code that I have put in my XSLT File:
<xsl:when test="contains($subject, 'SR#')">
<xsl:element name="Field">
<xsl:attribute name="Name">
<xsl:text>a_eco_parentObjectType</xsl:text>
</xsl:attribute>
<xsl:value-of select="'ServiceReq'"></xsl:value-of>
</xsl:element>
<xsl:element name="Field">
<xsl:attribute name="Name">
<xsl:text>a_eco_parentObjectID</xsl:text>
</xsl:attribute>
<xsl:analyze-string select ="$subject" regex="\s*[Ss][Rr]#([0-9]+)\s*">
<xsl:matching-substring>
<SR>
<xsl:value-of select="regex-group(1)"></xsl:value-of>
</SR>
</xsl:matching-substring>
</xsl:analyze-string>
</xsl:element>
The variable $subject contains the Subject line of the Email file that is being processed. The output file just contains:
ServiceReq
and I have an error message: :Error in loading Hierarchical Object XSLT file(s)

Answer 1

Here a solution :)
<emails>
<email>
<subject>RE: SR#51417: D_SATTER-NOV60LKA-I_G-A0201244</subject>
</email>
<email>
<subject>RE: Sr#565465: D_SATTER-NOV60LKA-I_G-A0201244</subject>
</email>
</emails>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="text" />
<xsl:template match="subject">
<xsl:variable name="v" select="." />
<xsl:analyze-string select="$v" regex="\s*[Ss][Rr]#([0-9]+)\s*">
<xsl:matching-substring>
<SR>
<xsl:value-of select="regex-group(1)" />
</SR>
</xsl:matching-substring>
<xsl:non-matching-substring>
<subject>
<xsl:value-of select="$v"/>
</subject>
</xsl:non-matching-substring>
</xsl:analyze-string>
</xsl:template>
</xsl:stylesheet>