regex pattern match in XSLT - regex

Question

I've the below XSL template
<xsl:template match="para">
<xsl:analyze-string select="." regex="\d+(?=[-, \d]*$)">
<xsl:matching-substring>
<xsl:variable name="prent">
<xsl:for-each select="document('C:\Users\u0138039\Desktop\Proview\SG\Commentary_SG_XML-03032014\SG-Singapore Precedents of Pleadings\title.xml')/entry/file">
<xsl:value-of select="normalize-space(document(concat('C:\Users\u0138039\Desktop\Proview\SG\Commentary_SG_XML-03032014\SG-Singapore Precedents of Pleadings\',./#name))//chapter/title[//page/#num=regex-group(1)])"/>
</xsl:for-each>
</xsl:variable>
<xsl:variable name="cha">
<xsl:value-of select="substring-before(substring-after($prent,'CHAPTER '),' ')"/>
</xsl:variable>
<xsl:variable name="size">
<xsl:value-of select="string-length($cha)"/>
</xsl:variable>
<xsl:variable name="conct">
<xsl:choose>
<xsl:when test="$size>'1'">
<xsl:value-of select="concat('er:#SPPR_CH_',$cha,'/pg_',regex-group(1))"/>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="concat('er:#SPPR_CH_0',$cha,'/pg_',regex-group(1))"/>
</xsl:otherwise>
</xsl:choose>
</xsl:variable>
<a href="{$conct}">
<xsl:value-of select="regex-group(1)"/>
</a>
</xsl:matching-substring>
<xsl:non-matching-substring>
<xsl:value-of select="."/>
</xsl:non-matching-substring>
</xsl:analyze-string>
</xsl:template>
and below XML
<para>this is 1989 representing text 245</para>
<para>this is sample text 235</para>
<para>this is 234 sample text with comma seperator 345,756</para>
when i run this it is throwing me an error as below.
Invalid regular expression '\d+(?=[-, \d]*$)' - Details: - XTDE1140: The effective value of the 'regex' attribute of the <xsl:analyze-string> instruction must conform to the required syntax for regular expressions
here what i'm trying to achieve is, to get the number at the end of the text, ignoring any other characters, when i tested the regex, it is working fine. and it is here, but when i implement the same in my XSLT, it is throwing me an error.
The expected output is
<a href="245"/>
<a href="235"/>
<a href="345"/>,<a href="756"/>
please let me know how can i fix this.
Thanks