Re: [RFC] Add :invisible face attribute

[Jim Porter]

On 12/18/2024 8:52 AM, Eli Zaretskii wrote:
> > From: Michal Nazarewicz <mina86@mina86.com>
> > Date: Wed, 18 Dec 2024 17:08:12 +0100
> >
> > Introduce :invisible face attribute which makes foreground to be the
> > same as background rendering the text invisible; or when :invert-video
> > is also in effect, background is the same as foreground.
[snip]
> A new face attribute adds quite a bit of complexity, so we should
> really believe this is a good idea.  Given that this can already be
> achieved without a new attribute, I'm not sure.  Is this really a
> frequent need/situation?
>
> But let's see what others think about this.

I'm just brainstorming here, but could Org use a display spec with 
specified spaces[1] to make Emacs render a space of the appropriate 
width? That requires a bit of computation, but it's how 
'visual-wrap-prefix-mode' and SHR handle (roughly) similar sorts of things.

If it's too difficult to get the existing specified spaces to work 
properly here, maybe we could enhance them? For example, perhaps you 
could have a display spec like this:

  '(space :width "**")

Which would mean "make a space as wide as the string '**'". That might 
even allow simplifying some of the code in 'visual-wrap-prefix-mode' 
(specifically, the parts that compute the width of the prefix; see 
'visual-wrap--content-prefix').

Still, if the existing specified space code is enough, it's probably 
best not to add even more complexity to it.

[1] 
https://www.gnu.org/software/emacs/manual/html_node/elisp/Specified-Space.html