bug#15917: 24.3.50; manual: mention keys reserved for users

[Stefan Kangas <stefan@marxist.se>]

Michael Heerdegen <michael_heerdegen@web.de> writes:

> (info "(emacs) Keymaps") doesn't tell anything about keys reserved for
> users (C-c LETTER).  BTW, this was the case some time ago, see
>
>   ftp://ftp.gnu.org/old-gnu/Manuals/emacs/html_node/emacs_492.html

New URL:
https://ftp.gnu.org/old-gnu/Manuals/emacs/html_node/emacs_492.html

> Users reading the users manual should have a chance to find this
> essential information, because getting used to bindings you cannot keep
> because of collisions you find later is very annoying.  I propose to add
> a sentence describing that C-c LETTER key sequences are reserved for
> users.  It would also be suitable for "(emacs) Init Rebinding", but
> somewhere it should be said.

The text on the above link was removed in:

    commit 8ba46c89bc0c2dccc9e51f1533dd127ecc125fbd
    Author: Chong Yidong <cyd@stupidchicken.com>
    Date:   Sat Sep 19 21:23:21 2009 +0000

OTOH, in `(elisp) Key Binding Conventions' we say:

   • Don’t define ‘C-c LETTER’ as a key in Lisp programs.  Sequences
     consisting of ‘C-c’ and a letter (either upper or lower case) are
     reserved for users; they are the *only* sequences reserved for
     users, so do not block them.

It's not clear to me why this convention was removed from the user
manual.  Should it perhaps be added back in?