I have the following XML file:
<rdf:RDF>
<policy:Policy rdf:ID="policy_N100CE">
   <deontic:actor rdf:resource="constraint_N10101"/>
   <policy:grants rdf:resource="deontic_N100D1"/>
   <policy:context rdf:resource="context_N100D9"/>
 </policy:Policy>
 <deontic:Permission rdf:ID="deontic_N100D1">
   <deontic:actor rdf:resource="constraint_N10101"/>
   <deontic:action
rdf:resource="http://ontology.ihmc.us/PolicyAction.owl#AddPolicyAction"/>
   <deontic:constraint rdf:resource="constraint_N100EB"/>
 </deontic:Permission>
 <constraint:SimpleConstriant rdf:ID="context_N100D9">
   <constraint:subject
rdf:resource="urn:KAoS#AddPolicyAction-Subclass-For-Policy-0cf0108c-010f-0000-8000-0000deadbeef-For-Property-ControlInstances0"/>
   <constraint:object rdf:resource="constraint_N100CE"/>
   <constraint:predicate
rdf:resource="http://ontology.ihmc.us/PolicyAction.owl#involvedPolicy"/>
 </constraint:SimpleConstriant>
 <constraint:SimpleConstriant rdf:ID="constraint_N100CE">
   <constraint:subject
rdf:resource="urn:KAoS#AddPolicyAction-Subclass-For-Policy-0cf0108c-010f-0000-8000-0000deadbeef-For-Property-ControlInstances0"/>
   <constraint:object
rdf:resource="http://ontology.ihmc.us/ActionStatus.owl#Accepted"/>
   <constraint:predicate
rdf:resource="http://example.lornet.sfu.ca/nkaviani/departments/objects/instances.owl#value"/>
 </constraint:SimpleConstriant>
 <constraint:SimpleConstriant rdf:ID="context_N100D9">
   <constraint:subject
rdf:resource="urn:KAoS#AddPolicyAction-Subclass-For-Policy-0cf0108c-010f-0000-8000-0000deadbeef-For-Property-ControlInstances1"/>
   <constraint:object rdf:resource="constraint_N100CE"/>
   <constraint:predicate
rdf:resource="http://ontology.ihmc.us/Action.owl#hasObjectContext"/>
 </constraint:SimpleConstriant>
</rdf:RDF>

and I have used the following construct to store some of the elements
in a variable based on an equality between the values of the
attributes:

<xsl:param name="contextID" select="policy:context/@rdf:resource"/>
<xsl:variable name="contexts">
	<xsl:copy-of select="//constraint:SimpleConstriant[@rdf:ID = $contextID]"/>
</xsl:variable>

apparantly the variable "contexts" has stored the relevant information
but when I try to read it, using for-each or whatever else, nothing is
displayed. so the code below is not working:

<xsl:for-each select="xalan:nodeset($contexts)">
	<xsl:value-of select="constraint:SimpleConstriant/@rdf:ID"/>
</xsl:for-each>

while <xsl:copy-of select="xalan:nodeset$contexts)"/> shows that the
desired values are stored in the variable.

thanks,
-Nima