bug#37774: 27.0.50; new :extend attribute broke visuals of all themes and other packages

[Eli Zaretskii]

> From: Andrey Orst <andreyorst@gmail.com>
> Date: Wed, 16 Oct 2019 21:13:23 +0300
> Cc: Ergus <spacibba@aol.com>, 37774@debbugs.gnu.org
> 
> (defface foo...)
> (when (>= emacs-major-version 27)
>   (set-face-attribute foo... :extend t))

Yes, that could work as well.

My pint is that making defface version-dependent is very easy.