category query hypermedia description

Hi,

Atomserver uses category queries to allow filtering of feeds based on atom categories.
http://atomserver.codehaus.org/docs/categories.html#Queries

This is a really nice facility, but I am wondering how to describe it in hypermedia.
AtomPub says nothing about filtering, so this is left up to the reader.

Is a description of the format specification enough?  I don't think so, since what you
would want to do in a RESTful API is have forms or templates fed to the client which
would allow client-side URI generation based on rules embodied in the hypertext.

But is this impossible with prefix notation boolean logic?

Thanks for your ideas or comments!

Peter Rushforth