+ ;; KLUDGE: it so happens that at present (2009-10-22) none of
+ ;; the external formats defined with
+ ;; define-multibyte-encoding can encode the unicode
+ ;; replacement character, so we hardcode the preferred
+ ;; replacement here.
+ #\?
+ (block size
+ (mb-char-len (or (,ucs-to-mb (char-code byte))
+ (return-from size 0))))