bug#50364: 27.2; EDT mode Xmodmap related documentation needs updating

[Eli Zaretskii]

> Date: Fri, 3 Sep 2021 23:25:21 +0000 (UTC)
> Cc: Charles Aylmer <ca22@cam.ac.uk>
> From:  Hin-Tak Leung via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> Been fighting with EDT mode configuration for a few weeks. 
> 
> The fundamental problem is that all the Xmodmap related instruction in
>     https://git.savannah.gnu.org/cgit/emacs.git/tree/doc/misc/edt.texi#n418
> and the entire section from about
>     https://git.savannah.gnu.org/cgit/emacs.git/tree/doc/misc/edt.texi#n325
> to
>     https://git.savannah.gnu.org/cgit/emacs.git/tree/doc/misc/edt.texi#n530
> is significantly outdated, by about a whole decade.
> 
> Modern Linux - and also Sun Workstations which have Gnome as desktop - 
> supports
> plug-and-play keyboards and mouses with X Keyboard Extension, and would 
> periodically
> reset any manually applied xmodmap settings; and also since about Gnome 3.6
> (around 2010), ignores .Xmodmap .
> 
> The proper way of remapping the Num_Lock key to EDT's GOLD key usage
> is via a custom keyboard layout with X Keyboard Extension. Failing that,
> the Apple family of xkb keyboard models, "Apple laptop", and "Apple Aluminium 
> (*)", 
> apple_laptop/applealu_ansi/applealu_iso/applealu_jis , have a definition
> for the Clear key at that key location.

Thanks.  Would you like to write some text that explains how to
achieve this on modern platforms?  We could then update or augment
what the manual says as appropriate.