To begin the schema work I used the schema generator in

   http://xml.mherman.org/index.php/trang/generate

using a few sample psml files from the "examples" directory.

(The 'trang' converter can also be used for this)

Then, I used this link for the "annotations" free-form spec:

  http://www.microhowto.info/howto/match_arbitrary_content_using_relax_ng.html

The RELAX-NG compact-form tutorial contains information on all the features
used.
