how to keep frame on top of stack?

[Drew Adams]

Anyone know a way to keep a particular frame on top? For example, a
temporary buffer like *Completions*, if displayed in its own frame?

I can give the frame an `auto-raise' property (which only raises it when the
frame is selected), or explicitly raise it at any given time, but I would
like it to stay on top for its lifetime (or until I lower it), even if other
frames are created or selected, and without my having to explicitly re-raise
it.

It would be great if there were a frame-parameter to specify the stacking
priority, or at least one to specify that a frame is to remain on top, but I
don't see such a parameter. With it, you could of course change a frame's
stacking priority at any time, but without making such a change, the
priority would stay the same.

Obviously, if two frames both specified the same stacking priority (e.g.
top), there would need to be a rule to determine which wins, etc.

[Sending to emacs-devel, not help-gnu-emacs, since this seems more like a
feature request. But I would still be interested in any workaround to solve
the problem. Thx.]