Major Section: PROGRAMMING
(Char-downcase x) is equal to #a when x is #A, #b when x is
#B, ..., and #z when x is #Z, and is x for any other character.
The guard for char-downcase requires its argument to be a standard
character (see standard-char-p).
Char-downcase is a Common Lisp function. See any Common Lisp
documentation for more information.