Generating custom class attribute for HTML output

Hi all,

What I have:

        <variablelist>
          <varlistentry role="REQ">
          <term>REQ-</term>
          <listitem>
            <para>This is an example requirement.</para>
          </listitem>
         </varlistentry>
        </variablelist>

What I want in my HTML output:

<dl>
 <dt class="REQ"> ... </dt>
 <dd class="REQ"> ... </dd>
</dl>

In the default, this do not work.

So I'm refering to http://www.sagehill.net/docbookxsl/HtmlCustomEx.html#CustomClassValues

where I added this snippet to my HTML customization layer:

<xsl:template match="varlistentry[@role = 'REQ']" mode="class.value">
  <xsl:value-of select="'REQ'"/>
</xsl:template>

But this also not get me the wished result? Any ideas?

Many thanks in advance.

Halm