untestable assertions

In our document text, we have a number of assertions which aren't readily expressible as an XPath expression. Jon's latest constraint to disallow cyclic references being one, requiring UTF-8/UTF-16 being another.

Something we could consider is adding assertions as placeholders to our pattern detector, as suggested by Rick, here:

http://www.oreillynet.com/xml/blog/2007/03/expressing_untested_and_untest.html

Paul