> >    <xsl:variable name="file">
          ....
> >    </xsl:variable>
> 
> This creates a result tree.

Correct.

>  You need to use a node-set extension to convert this to a  node-set.

But you don't need a node-set. You can supply a string to the document()
function, and RTF-to-string conversion is automatic. 
> >
> >   <xsl:variable name="file" select="concat($SHARE, 
> $bizcase/@lang, '/descriptors/', @descriptor)"/>
> 
> This creates a node-set.

No, it creates a string.

Michael Kay
http://www.saxonica.com/