Originally raised in
http://lists.w3.org/Archives/Member/w3c-xml-schema-wg/2006Aug/0016.html by
Kohsuke Kawaguchi <Kohsuke.Kawaguchi@Sun.COM>

- For my problem domain, being able to identify particles and
   attribute uses would have been very much desirable. So I find it
   unfortunate that this version of SCD decided to skip them.

   For example, a JAXB user would often like to say "this use of
   xml:lang attribute in this complex type, I'd like it to be mapped to
   a Java property 'language'", and this kind of "description" is best
   attached to the attribute use, since different use of xml:lang maybe
   be bound differently. A similar use case exists for particles.