Well, from reading this thread I expected it to be sorted by priority.

On Tue, Jun 20, 2023 at 2:01 PM Eli Zaretskii <eliz@gnu.org> wrote:

> > From: Milan Jovanovic <milanj@gmail.com>
> > Date: Tue, 20 Jun 2023 13:32:04 +0200
> > Cc: João Távora <joaotavora@gmail.com>,
> >  Stefan Monnier <monnier@iro.umontreal.ca>,
> >  Krzysztof Klimonda <kklimonda@syntaxhighlighted.com>,
> >  64101@debbugs.gnu.org
> >
> > I do expect that but I’m talking about order of overlays that have the
> same start/end (and all of them have the same before-or-after-string
> property).
> > If you have more than one overlay with the same start/end and all of
> them have the same before-or-after-string property one order will be
> ascending and other descending (in regard to priority).
>
> And you don't expect that from the Emacs display?
>