create a list of elements

Hi,
 
     I want obtain n elements form one xml file, to after use it to compare
 with
 others elements in another xml file, how can I do that?
 
 example, in the xslt :
 
    <xsl:for-each select="controlfield">
         <xsl:element name="xsl:variable">
             <xsl:attribute name="name"> elementList </xsl:attribute>
             <xsl:value-of select="@tag"/>
         </xsl:element>
   </xsl:for-each>
 
 the result that I like to obtain is the variable elementList contain
 something like this
 elementList = [elem1, elem2, elem3,....,elemN] the elemI , I=1,..N became
 form the all tags
 from the element controlfield, in a xml file...
 that elements will be used in another xslt....
 this is possible in xslt ?
 
 Thanks All
 

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