Re: Faces: How to clear an attribute while continuing to inherit other attributes?

[Eli Zaretskii <eliz@gnu.org>]

> From: Dave Goel <deego3@gmail.com>
> Date: Wed, 9 Oct 2019 22:42:50 -0400
> 
> Emacs allows us to set a's foreground to nil (instead of 'unspecified), but it magically becomes 'unspecified
> when queried. That's not what I was aiming for. That is because 'unspecified means actually rendering face 'a
> would yield yellow, the color inherited from 'b instead of the default foreground.
> 
> Here's a test:  
> 
> (progn
>   (defface a nil "")
>   (defface b nil "")
>   (set-face-attribute  'b nil :foreground "yellow")
>   (set-face-attribute 'a nil :inherit 'b)
>   (set-face-attribute 'a nil :foreground nil)
>   ;; let's chase how 'a would render:
>   (face-attribute 'a :foreground nil t))
> 
> => "yellow"
> 
> We expected either "white", the default foreground.

What do you mean by "default foreground" here? is that the foreground
of the default face, or the foreground of whatever other face(s) that
are merged to produce the appearance of a character on display?