Subject: bug#24706: 26.0.50; Minor mode functions should do strict argument type checking

From: Drew Adams <[email-masked]>
Date: Sun, 16 Oct 2016 09:12:14 -0700 (PDT)

> (define-minor-mode foo-mode nil)
> its docstring will be
> 
> "Toggle Foo mode on or off.
> With a prefix argument ARG, enable Foo mode if ARG is
> positive, and disable it otherwise.  If called from Lisp, enable
> the mode if ARG is omitted or nil, and toggle it if ARG is ‘toggle’."
> 
> This appears to indicate that (foo-mode 'banana)
> should disable foo-mode, but it enables it.

No, it does not suggest that.  But to be clearer, it should
probably explicitly address the non-nil and non-`toggle' case,
like so:

  If called from Lisp, enable the mode if ARG is omitted or
  nil, toggle it if ARG is ‘toggle’, and disable it if ARG is
  any other non-nil value.

(And place the Lisp description in a separate paragraph
from the interactive description.)

> I think minor modes should simply not allow anything but
> integers and 'toggle for ARG, avoiding this confusion.

Why?  There is no confusion possible, once the doc string 
explicitly speaks about all possible argument values.

Why would you change the behavior, instead of just clarifying
the doc?