Filtering, xslt 2.0

Input xml contains
<data>
...
   <membership>....</membership>
</data>
where membership can be one of a b c d

cmd line param
membership=a
could be membership=a,b,c

How to 'choose' only those matching the param values?
<xsl:template match="data">
<xsl:if test="$membership =./membership">
    <xsl:message>
   <xsl:value-of select='membership_type'/>
 </xsl:message>
    <xsl:apply-templates/>
  </xsl:if>
..


How to pass a list, and then check for membership
of that list, one or more times?

Any help appreciated.

regards





-- 
Dave Pawson
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