overlays with higher priority than region [was: no good way to highlight rectangle while region is highlighted]

[Drew Adams]

>     Summary of this message: This is a feature request for (1) the
>     possibility that some overlays can have priority over the use of the
>     region face, and/or (2) a variant of the ?box? face feature where the
>     vertical lines of the box take no extra space.
>
RMS> (2) sounds terribly low-level.  (1) is cleaner.

RMS> I think (1) could be implemented with a change in
RMS> face_at_buffer_position. For instance, we could define a
RMS> certain priority for the region, so that overlays whose
RMS> priority exceeds that cover the region.
RMS> It doesn't look terribly hard, but you need to think carefully
RMS> to prove that you store the value into *ENDPTR in all cases.

Did this get dropped? I too would like to see the possibility of having an
overlay that has higher priority than the region. One use case is
highlighting a line within the region.

[Please don't suggest other ways to draw attention to the line, here (e.g.
display-table, fringe). That is just an example. I would like to be able to
have an overlay with a higher priority than the region - I'm not interested
in this example per se.]