bug#67794: 30.0.50; mouse-face is not respected on SVG images

[Eli Zaretskii]

> From: Manuel Giraud <manuel@ledu-giraud.fr>
> Cc: alan@idiocy.org,  67794@debbugs.gnu.org
> Date: Wed, 13 Dec 2023 09:18:56 +0100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> From: Manuel Giraud <manuel@ledu-giraud.fr>
> >> Cc: Eli Zaretskii <eliz@gnu.org>,  67794@debbugs.gnu.org
> >> Date: Tue, 12 Dec 2023 17:35:18 +0100
> >> 
> >> BTW, mouse-face is a standard Emacs face so I don't why it seems not
> >> to be handled by one of those calls.
> >
> > No, mouse-face is not a face, it's a text property.
> 
> Ok.  I thought it was a face because it is declared as MOUSE_FACE_ID in
> the face_id enum.  And as Alan talked about the 3 calls to lookup_image,
> I thought that it could be called MOUSE_FACE_ID as argument.

It behaves exactly like a face, and has the same attributes, thus the
MOUSE_FACE_ID enumeration.  But it is handled specially by the display
engine, because it changes the appearance depending on mouse pointer
position, without any changes to the mouse-face definition itself.