Re: [RFC] Add :invisible face attribute

[Psionic K]

> I recall there being some debate about how it should work; for example, if 
> instead we should support RGBA for :foreground

Coupling color and alpha when composing faces would make it really
difficult to work with regions, which will have a lot of faces and
would have to be interrogated for each color.

In any case, occluding text without causing re-flow of the contents is
important.  I've used the hacky version of such functionality in both
dslide and MoC and I'm sure people with greater imagination will only
use it better.