Replace UPPER with lower?

Does Calibre not have a replacement expression to replace a match with the lowercase version of the match? I've tried the usual regex means of doing so (\L&, e.g.), and nothing seems to work.

I really don't want to use regex functions (and have to write a function) to do something this trivial, so I assume I'm missing something. I've read the pertinent section of the user's guide, and don't see anything mentioned there, either. (I searched for "lower" everywhere in the regex page.)