Re: slow redisplay after changing cursor color

[Richard Stallman]

    I didn't change defface / custormize-face to reject :inherit from face
    with the face-no-inherit property  (it would be nice, but I don't quite
    know how to do that).

The code that processes the user's input could check for a :inherit
attribute, and look at the face to be inherited from.

However, :inherit is not the only way to use a face.

What happens, with your code, if someone simply gives an overlay a
face property of `cursor-color'?  That would realize a face using the
color from `cursor-color', right?  With your change, that won't update
either if the face is changed.  Or at least I think so; what actually
happens?

If it's the way I expect, I think we should urge users not to do that,
or else make it get an error, or else make it work.

    Is it necessary to add anything to NEWS or the manuals about this ?

It should tell people that they can't, or shouldn't, use certain faces
in certain ways.  I don't think it needs to describe the mechanism
such as the face-no-inherit property.