Ah, typing too quickly and I missed that we were using clsName for
comparison, not as a target variable to fill.  I don't have much time,
so I"ll only give it one more shot before concluding that I'll have to
wait till I have time to look at it closer.

<xsl:choose>
<xsl:when test="document(Second.xml)/SubConcepts/SubConcept[1]/Value[$clsName=text()]">
<xsl:variable name="nodeToProcess"
select="document(Second.xml)/SubConcepts/SubConcept[1]/Value[$clsName=text()]"/>
</xsl:when>

<xsl:otherwise>
<xsl:variable name="Values"
select="document(Second.xml)/SubConcepts/SubConcept/Value/@name[.=$clsName]"/>
<xsl:variable name="nodeToProcess" select="$Values[1]">
</xsl:otherwise>
</xsl:when>

Cheers
Rahil