Re: Making `x-underline-at-descent-line' a face attribute

[Jim Porter]

On 1/6/2022 12:43 AM, Eli Zaretskii wrote:
> > From: Jim Porter <jporterbugs@gmail.com>
> > Date: Wed, 5 Jan 2022 21:08:57 -0800
> >
> > What about enhancing the :box attribute further to allow different
> > widths (and possibly colors) for each of the 4 sides?
>
> The width part is already supported.  We could make the value of
> :color be a cons cell as well, if that is useful (is it?)

Looking at the docs for :box, I only see the ability to set separate 
vertical and horizontal widths (but not to set all 4 sides to different 
values). The latter would be useful in some cases, for example to make 
the tab-bar tabs look more like tabs. You could specify a box with a 
border on all sides but the bottom for the active tab, and a border 
*only* on the bottom for inactive tabs, so you get something like:

              +----------+
    inactive  |  active  |  inactive
  ------------+          +------------

One benefit of making :color a cons cell is that it would be possible to 
create an effect like `:style released-button', but allow the programmer 
to control the exact colors to use. That could be useful in some 
situations. For instance, the modeline could have a border at the top 
and bottom (but not the sides) with different colors to make it appear 
raised. I tried using `:style released-button' for that, but it appears 
to only support a :box with non-zero widths on all sides.

> But mixing :box and :underline is IMO not a good idea.  They are
> separate attributes.

I think I agree. From the original message, it sounded like the goal was 
to get a border around the modeline, so using :underline isn't the ideal 
option semantically. If :box were more flexible, it'd be possible to use 
that to draw borders around things, even if that "border" was just on 
the bottom (making it look similar to an underline).