Indices

I'm looking at the emacs texinfo markup.

It has indexterms marked by 'class', e.g. index terms for variables, 
functions, keys etc.

Is there such capability in docbook please?

I can use

  <indexterm class='variable'>
             <primary>track-eol</primary>
          </indexterm>

But is there any mechanism to group index entries by some attribute 
value? I don't think the zone attribute is applicabe?

regards

-- 
Dave Pawson
XSLT, XSL-FO and Docbook FAQ
http://www.dpawson.co.uk