Feedback and improvements welcome!
It grew out of some years of thinking about remaining gaps with Schematron and XML query languages, and some experience with very large corpuses where dozens of different data sources (indeed, scores of sources, over time) fed very different documents to be converted to a common kitchen-sink transitional DTD: having a common schema made it look like it had been reduced to an N:1 problem, but this disguised that the documents were clustered into, in effect, different discrete languages depending on their source.
Regards
Rick