RE: mouse-face vs. transient-mark-mode

[Drew Adams]

    When an overlay property of 'mouse-face 'highlight is set on a line,
    and transient mark mode is on, and you attempt to drag out a new
    region in the line, the region mark overlay does not show, and
    significant flickering occurs as you drag the mouse inside the
    highlighted text.  As soon as the mouse moves out of the mouse-face
    area (either during the drag or after it's completed), the mark face
    is visible.  The flickering is present even when transient-mark-mode
    is disabled..

    Is it possible to set a priority on either mouse-face or the region
    highlight property to have the former yield to the latter?

I can't answer your question definitively, JD, but I think the answer is
"no".

Caveat - The rest of this message is about a possible new feature, so it is
not intended for real discussion before the release. I mention it now as
food for thought, because of JD's request.

I mentioned a few months ago that I thought it be great if one could have a
mouse-face text property combine visually with the face text property:

    Ideally, I would love to be able to use underlining _without
    removing any font-lock highlighting_; that is, simply
    underline the text when you point to it, without changing
    any of its other properties. That's the behavior in
    most Web browsers.

I was speaking of using underline (for example) as the mouse-face, and I
mentioned only font-lock highlighting, but the general idea is to let the
mouse-face show up in combination with the face. That way, you could see the
normal (font-lock) highlighting as well as things like the region.

Of course, the desired effect would only be achieved if the two (mouse-face
& face) combined well. JD's request for being able to set a precedence might
fit here.

As I mentioned previously:

    I'm not sure if that's easy to do, or even feasible, in Emacs

I don't know much about face inheritance, but perhaps that could be used
somehow in this regard.