tag 11299 + patch
quit

> `(elisp) Derived Modes' says, "Only the (still experimental and
> unadvertised) command `customize-mode' currently uses this."
>
> It has said this since at least Emacs 22.

Indeed that seems long enough to declare it non-experimental. So I
propose removing that phrase and just say "The command
`customize-mode' uses this", as in the current docstring of
`define-derived-modes'. Any objections?

> It is OK for the default to be the current major mode, but the use
> of a prefix arg (completion for a mode name) should at least allow
> for minor modes as well as major modes.

AFAICT it always allowed entering any mode with a prefix argument,
it's just a matter of updating prompt and docstring (cf
http://debbugs.gnu.org/cgi/bugreport.cgi?bug=23649).