sub equations

Dear Docbook Apps,
Wanting several similar equations to share a title and number, I
decided I would like to have support for sub-equations (ex, Equation
2.1-a). I have never extended the docbook dtd or stylesheets, and know
it would be a large undertaking for myself. I was wondering if anyone
has already implemented this modification - have you? please speak up
:]

It is probably a modification that an engineer would make, rather than
a mathematician... we're always coming up with sub equations that are
actually not so important...

Regards,
--
http://chrischiasson.com/contact/chris_chiasson