RE: link appearance and soft face properties

["Drew Adams" <drew.adams@oracle.com>]

    > Providing a link face (that inherits etc.) and using it for all
    > links (i.e.  places where the code in fact "follows a link" upon
    > click) would let users customize, in a single place, how links
    > appear.  (If we provided buffer-local faces, users would also be
    > able to easily customize link appearance on a per-buffer basis.)

    I can't imagine other useful face attributes for the `link' face
    than underline.  For example, changing its foreground color will
    make different faces inheriting from it indistinguishable (like
    visited and unvisited links in Info, or file names and line numbers
    in grep and compilation).

    So I see the `link' face mainly as a way to turn link underlining off.
    But then it should be possible to do that on a per-buffer basis to
    turn underlining off in some modes (e.g. in grep and compilation)
    but leaving it in others (e.g. in Info).

Turning underlining on/off is certainly one application of this.

There is also the choice of whether links should use a special face (e.g.
underlining, or blue text) or a special mouse-face or both. WRT the face
property, this means whether or not links should be discernable without
moving the mouse over them.

Emacs has used different ways to represent links in the past, I believe.
Links in Info are now underlined and blue, and a mouseover removes the
underlining and the blue foreground and makes the background green (by
default). Links in Dired use the same mouseover highlighting, but do not use
any highlighting for the face property. And so on.

The feature I was proposing would let Emacs developers and Emacs users:

1) Define the global (default) appearance of links (both face and mouse-face
properties) in a single place.

2) Define the local appearance of links on a per-buffer (e.g. per mode)
basis.

And the same idea would apply to buttons and other user-interface objects
that use faces.