bug#37700: 27.0.50; undo mouse-drag-and-drop-region ineffective

[Eli Zaretskii]

> From: Mattias Engdegård <mattiase@acm.org>
> Date: Sat, 12 Oct 2019 18:42:30 +0200
> Cc: Tak Kunihiro <homeros.misasa@gmail.com>, tkk@misasa.okayama-u.ac.jp,
>         Eli Zaretskii <eliz@gnu.org>, martin rudalics <rudalics@gmx.at>
> 
> > So perhaps a better way to resolve this situation is to teach 'undo'
> > about drag-and-drop, so that it doesn't undo selectively immediately
> > after drag-and-drop?
> 
> Maybe --- can it be done within the current 'undo' framework, or would 
> drag-and-drop need to be special-cased? Did you have a particular approach in 
> mind?

I didn't figure out the details, I only had a general idea.  I thought
about doing that inside 'undo', perhaps have a list of commands for
which an immediate 'undo' will disregard an active region.