bug#21025: tabulated-list.el: It should preserve header line set by derived modes. (Encl. a suggested PATCH)

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

> >> -      (overlay-put tabulated-list--header-overlay 'face 'underline))))
> >> +      (overlay-put tabulated-list--header-overlay
> >> +                   'face '(:overline t :underline t :weight bold)))))
> >
> > This might be more controversial, though.  I think it looks nice, but
> > some people don't like so many lines.  Perhaps it should be a defface,
> > so that people can change this themselves?  The default could be what
> > you're describing, though.
> 
> I've now done this change and otherwise applied your patch.

This is a bad way to do things - makes it difficult
for users do customize the appearance.  Emacs is "the
extensible, customizable, self-documenting, real-time
display editor".

The right way to take care of what is essentially a
user's preference for column-header appearance is not
to change the hard-coded appearance but to define a
face for this in `tabulated-list.el'.  Then ALL users
can get the appearance they want just by customizing
that face.

The face can have whatever default appearance you
want: underline, underline and overline - whatever.
But let users customize a face; do not hard-code one.