DOCBOOK: section content type

Honored DocBooklians:

We'd like to be able to specify a content type for recursive 
section elements (somewhat similar to the class attribute 
for the article element).  

In particular, we'd like to identify some recursive sections 
as reference material.

The obvious solution would be the role attribute.  However, 
we'd like to keep the role attribute free for other hacks.

Would a reasonable workaround for section attributes be to 
add a subjectset in a sectioninfo element?  As in:

  <section>
    <sectioninfo>
        <subjectset scheme="attributes">
          <subject>
            <subjectterm id="contenttype">reference</subjectterm>
          </subject>
        </subjectset>
    </sectioninfo>
    ...

Or is that an unspeakably hideous abuse of the semantics?


Thanks for any suggestions, 


Erik Hennum