Re: link appearance and soft face properties

[Richard Stallman <rms@gnu.org>]

    If you are questioning whether such properties are really "hard" today, that
    is, whether they do not in fact allow for alternative display or
    interpretation as, say, sound, then I think the answer is "yes" - out of the
    box, Emacs does not allow for any alternative treatment for such properties:
    :underline always means "underline". The :underline text property simply
    determines whether or not the text in question is underlined. From Info:

That's right.

If you want something to underline in certain circumstances and do other
things in other circumstances, the way to do that is to define a face
with a conditional definition.

    In particular, I wanted to distinguish link text from underlined text. Just
    because some text might be underlined does not make it a link. To be a link,
    it must behave as a link. I suggested we provide a way to make a portion of
    text appear as a link - in whatever way that appearance might be manifested.

It is useful to have one way to say "make this text look like a link",
and the right way to do it is by defining a face called `link' and using
it in those places.