-;;; FIXME: Shouldn't we be testing for legality of
-;;; * START1, START2, END1, and END2 indices?
-;;; * size of copied string relative to destination string?
-;;; (Either there should be tests conditional on SAFETY>=SPEED, or
-;;; the transform should be conditional on SPEED>SAFETY.)
-;;;
-;;; FIXME: Also, the transform should probably be dependent on
-;;; SPEED>SPACE.