(defun byte-recompile-directory (directory &optional arg)
"Recompile every `.el' file in DIRECTORY that needs recompilation.
This is if a `.elc' file exists but is older than the `.el' file.
+Files in subdirectories of DIRECTORY are processed also.
If the `.elc' file does not exist, normally the `.el' file is *not* compiled.
But a prefix argument (optional second arg) means ask user,
for each such `.el' file, whether to compile it. Prefix argument 0 means
-don't ask and compile the file anyway."
+don't ask and compile the file anyway.
+
+A nonzero prefix argument also means ask about each subdirectory."
(interactive "DByte recompile directory: \nP")
(if arg
(setq arg (prefix-numeric-value arg)))