Somehow, annoyingly, I missed this last message earlier.
But I'd still prefer to thank you for your instructive answers.

Indeed, I have read about the evaporate property before,
but I have not used it before, so that I forgot about it.
I'm more or less sure that it will stick this time...

On Sat, 25 Feb 2023 at 14:42, Eli Zaretskii <eliz@gnu.org> wrote:

> > From: dalanicolai <dalanicolai@gmail.com>
> > Date: Sat, 25 Feb 2023 14:17:24 +0100
> > Cc: emacs-devel@gnu.org
> >
> > This is great! Indeed, it works perfectly now.
> > I think using the margins is just much more elegant.
> >
> > Although, I might have read about this behavior somewhere,
> > obviously, it was not clear to me that `erase-buffer` does not
> > remove the overlays. Maybe a warning/reminder about this could
> >  be added in the 'erase-buffer' docstring? What do you think?
> > I would be happy to create a patch for that (if desired).
>
> This is not related to erasing a buffer, it is related to deleting
> text "covered" by the overlay.  What happens in that case depends on
> the 'evaporate' property of the overlay, which is already described in
> the ELisp manual, see the node "Overlay Properties" there.
>