Hard: The appearance of a hard text property like :underline
always means the same thing: the text is underlined. Users can
decide to use it or not use it, but they cannot redefine it.
This is a weird statement. What should people who listen to
underlined text do? (They may want the underlined text to be
different from the rest.)
What should people who look at text, but for various reasons, use
colors, never underlines or other such modifications. (Setting in
their .emacs file.)
