XSL content:encoded troubles

Hi,

First of all, there's no XSL newsgroup so I'll have to post my question 
in the *mozilla.style and mozilla.xml newsgroup, because I don't know 
which one to use (and maybe these are both wrong).

My question is: should something like this work in Mozilla?

       <xsl:attribute name="description">
         <xsl:choose>
           <xsl:when test="content:encoded">
             <xsl:value-of select="content:encoded"/>
           </xsl:when>
           <xsl:otherwise>
             <xsl:value-of select="description"/>
           </xsl:otherwise>
         </xsl:choose>
       </xsl:attribute>

To read/assign the data of:

<content:encoded>
<content:encoded>

to the description attibute?

Please note that I am still learning so I might have made one or more 
errors, because I don't fully understand XSL yet, so it would be nice if 
anyone could help me with this problem.

Thank,
Michael