The XSLT function for generating a secondary sort key had been created in an accretive fashion, and ended up being very difficult to change because altering the sequence of the fifteen (so far) steps required manual adjustment of letter codes for all of them. I've now rewritten it in an optimized manner (optimized in the sense that it's probably slightly slower, but trivial to reorder or expand with new steps, as may happen next week).

I should do this sort of thing more often.