Here is an abstraction of my problem template:

 <xsl:template match="record">
   <xsl:param name="show-fields" />
   <xsl:variable name="this" select="." />

   <xsl:for-each select="str:tokenize($show-fields)">
     <xsl:message><xsl:value-of select="$this/field[@name=.]" /></xsl:message>
   </xsl:for-each>
 </xsl:template>

So <record> elements have child elements called <field> which each
have a @name attribute.

The given template should accept a parameter which is a list of field
names, and emit an <xsl:message> of each <field> element whose @name
is in that list.

Your textual description sounds as if you want
  <xsl:for-each select="field[@name = str:tokenize($show-fields)]">
    <xsl:message>
      <xsl:value-of select="."/>
    </xsl:message>
  </xsl:for-each>

	Martin Honnen
	http://msmvps.com/blogs/martin_honnen/