[relax-ng] Description of Jing's validation algorithm

I have written up a description of the validation algorithm used in Jing
(and I believe in MSV also):

  http://www.thaiopensource.com/relaxng/derivative.html

I would be grateful for reports of bugs or areas where the description is
not comprehensible.

I will announce this on xml-dev in a few days.  Hopefully this is enough to
make it relatively easy for people to implement RELAX NG validators.  I also
hope to write something on the algorithms needed to transform RELAX NG into
simplified form and to determine whether these are correct.

James