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

[D <d.williams@posteo.net>]

> I'm not sure I understand the problem, but can't you use :align-to in
> display properties to solve the alignment issues?

To provide a concrete example, consider the following (closed) issue:
https://github.com/integral-dw/org-superstar-mode/issues/9

The data structure org-superstar-todo-bullet-alist associates a todo
keyword with a character to be displayed.  The image shows the alignment
problem.  The compose-region solution to this is simply to compose each
character with a wide enough space, so the user simply has to use
"\N{EM SPACE}<character>" instead of ?<character> in the alist.
compose-region will then just superimpose the two and you get a "padded"
character.  It is very much possible that :align-to could fix this as
well, judging from the documentation it does sound like it can reproduce
this feature easily.  To see how well it works out I would likely have
to implement a display-based version first, though.

On a side note: Are there any quirks I should be aware of when
transitioning to the display property? I doubt there will be any
difference in terms of performance (contrast overlays, which my mode
can't afford use), but is there anything else I should be aware of?  I'm
asking in case there have been efforts like mine in the past which I am
not aware of.