Re: prettify-symbols-mode, derived modes, and compose-region

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: Eli Zaretskii <eliz@gnu.org>,  emacs-devel@gnu.org
> Date: Thu, 04 Mar 2021 21:30:33 -0500
> 
> You should definitely try, but I suspect it's not going to work
> well: :align-to wants to get an "absolute" position of the position
> where the flexible space ends whereas in your case you only know how
> wide "char + space" should be, but you don't know at which absolute
> column "char" will happen to be displayed, so you can't know to which
> column to :align-to.

If the width of the additional space is known, there's also the :width
display property.