Define a list variable in xslt

In my xsl transform the filename is passed as a parameter to the stylesheet. I want to do a certain set of actions if it is in a certain filelist. Right now I'm doing it this way;

<xsl:param name="specialFiles" select="'|a.xml|b.xml|'"/>

<xsl:template match="/">
   <xsl:choose>
        <xsl:when test="contains($specialFiles,concat('|',$FILENAME,'|'))" >
            <xsl:apply-templates select="abc" />
        </xsl:when>
        .....
        .....

This works, but quickly becomes messy when the specialFiles list grows. Is there a way to declare it like an array, and lookup quickly?