Thank you, Jim.

I have a tool that can give you a word list, sorted, with count of
occurrences. If that would help solve the problem.
There is a python tool that does this already (free) but I would be
interested in your XSLT solution.

A frequency counter written in XSLT 2.0 was posted in this list by
Michael Kay some time ago, I also have an FXSL implementation.

As for the concordance, I will give it a try -- whenever there's a day
or two of free time available.

I think that at least one algorithm has been described in the
literature, and there's a Haskell implementation.