"Add the usage info to the docstring DOC.
If DOC already has a usage info, then just return DOC unchanged.
The usage info is built from ARGLIST. DOC can be nil.
-ARGLIST can also be nil or a string of the form \"(fun ARG1 ARG2 ...)\"."
+ARGLIST can also be t or a string of the form \"(fun ARG1 ARG2 ...)\"."
(unless (stringp doc) (setq doc "Not documented"))
- (if (or (string-match "\n\n(fn\\(\\( .*\\)?)\\)\\'" doc) (not arglist))
+ (if (or (string-match "\n\n(fn\\(\\( .*\\)?)\\)\\'" doc) (eq arglist t))
doc
(format "%s%s%s" doc
(if (string-match "\n?\n\\'" doc)