you can't use xsl:attribute with xsl instructions


You can do
<xsl:variable name="x">
  <xsl:choose>
  ... what you had
</xsl:variable>
<xsl:for-each select="...">
 <xsl:sort select="zzz" data-type="{$x}"/>

David

 XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list