bug#49278: 28.0.50; Lisp Mode is for Common Lisp

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: João Távora <joaotavora@gmail.com>,
>   49278@debbugs.gnu.org
> Date: Tue, 29 Jun 2021 16:46:10 -0400
> 
> >>  (define-derived-mode lisp-mode lisp-data-mode "Lisp"
> >> -  "Major mode for editing Lisp code for Lisps other than GNU Emacs Lisp.
> >> +  "Major mode for editing Common Lisp code.
> > Here I'd prefer to mention CL without un-mentioning the other Lisps.
> > There's no reason to deny they exist or existed.
> 
> The question is to describe what this major mode is designed to do.

How do you suggest to do that in a concise enough way appropriate for
a doc string?

> People who want to look at Maclisp code (or other defunct dialects) will
> probably want to use `lisp-mode` for the simple reason that Maclisp is
> reasonably close to Common Lisp so it's the closest major mode we have
> to offer, but the user should not expect correct handling of Maclisp in
> those places where it differs from Common Lisp, because `lisp-mode` is
> written specifically for Common Lisp and not for Maclisp: compatibility
> with Maclisp has not been taken into account for more than 20
> years, AFAIK.

Did lisp-mode.el changed significantly during those 20 years? did
Maclisp change significantly?  If not, we don't have a problem more
that we had it back then, do we?