bug#34639: 26.1; Custom themes break terminal when switching to org-mode

[Eli Zaretskii]

> From: Richard Stallman <rms@gnu.org>
> Cc: contovob@tcd.ie, kisik21@fireburn.ru, 34639@debbugs.gnu.org
> Date: Fri, 01 Mar 2019 22:28:27 -0500
> 
> Why is it better if people use the display margins via
> linum (not core) rather than by an option in native line numbers?
> I don't see that it makes much difference to the issues of
> future maintenance.

It makes a difference because we can tell them to drop linum if they
have problems with display margins.  And because we don't have to deal
with bug reports about such conflicts.

> What happens if two features try to use the display margins?

You have a mess in the display margin area.  Even the size of the
margin can change unpredictably, because each feature changes it
according to its own logic.

> What does the interference look like?  I suppose they can't both work
> properly, but does it cause anything worse than that?

What can be worse in a real-time editor than a messed-up display?