XSL Using replace and matches to update values - xslt

Question

I am trying to update an old form that uses a data model that has changed, so any reference to the old model I want to replace with the new. I currently use the function matches to tell if I should preform the replace on the current string and then use the replace function to replace the value with the new one, the problem is that the regex used in the matches does not work with the regex in the replace.
<xsl:template
match="//*[contains(#*:default,'instance(''document'')/')
mode="pass">
<xsl:variable
name="regex"
as="element()*">
<regex>instance('document')/doc_type/description</regex>
<regex>anotherRegex</regex>
</xsl:variable>
<xsl:variable
name="replacement"
as="element()*">
<replacement>xxf:get-request-parameter('documentDesc')</replacement>
<replacement>replacedRegex</replacement>
</xsl:variable>
<xsl:element name="{name()}">
<xsl:for-each select="#*">
<xsl:choose>
<xsl:when test="name() = ('xxf:default')">
<xsl:attribute name="xxf:default">
<xsl:analyze-string
regex="{concat('(',$regex[1],'|',$regex[2],')')}"
select=".">
<xsl:matching-substring>
<xsl:if test="matches(.,$regex[1])">
<xsl:value-of select="replace(.,$regex[1],$replacement[1])" />
</xsl:if>
<xsl:if test="matches(.,$regex[2])">
<xsl:value-of select="replace(.,$regex[2],$replacement[2])" />
</xsl:if>
</xsl:matching-substring>
<xsl:non-matching-substring>
<xsl:value-of select="." />
</xsl:non-matching-substring>
</xsl:analyze-string>
</xsl:attribute>
</xsl:when>
<xsl:otherwise>
<xsl:attribute name="{local-name()}"><xsl:value-of select="." /></xsl:attribute>
</xsl:otherwise>
</xsl:choose>
</xsl:for-each>
</xsl:element>
</xsl:template>
Current XML:
<xf:bind id="clinic-bind"
name="clinic"
xxf:default="instance('document')/doc_type/description"
type="xf:string"/>
What I want to turn it into:
<xf:bind id="clinic-bind"
name="clinic"
xxf:default="xxf:get-request-parameter('documentDesc')"
type="xf:string"/>

Answer 1

So the Problem was basicaally I had to escape the '()' characters in the regex variable.
So I ended up with
<regex>instance\('document'\)/doc_type/description</regex>
In the regex part.