(defun mm-find-mime-charset-region (b e &optional hack-charsets)
"Return the MIME charsets needed to encode the region between B and E.
-Nil means ASCII, a single-element list represents an appropriate MIME
+nil means ASCII, a single-element list represents an appropriate MIME
charset, and a longer list means no appropriate charset."
(let (charsets)
;; The return possibilities of this function are a mess...