bug#43713: 26.3; doc of `define-generic-mode'

[Drew Adams]

The doc string says nothing at all about what a generic mode is.

(elisp) `Generic Modes' says only this:

  "Generic modes" are simple major modes with basic support for comment
  syntax and Font Lock mode.

Is that all users need to know about a generic mode?

Can we at least say something like that in the doc string?



In GNU Emacs 26.3 (build 1, x86_64-w64-mingw32)
 of 2019-08-29
Repository revision: 96dd0196c28bc36779584e47fffcca433c9309cd
Windowing system distributor `Microsoft Corp.', version 10.0.18362
Configured using:
 `configure --without-dbus --host=x86_64-w64-mingw32
 --without-compress-install 'CFLAGS=-O2 -static -g3''