Overlays priorities and text properties

[Lennart Borgman (gmail)]

There is a comment in

  (info "(elisp) Overlay Properties")

saying "please avoid using negative priority values as we have not yet 
decided just what they should to".

I just have a case where I want to put a background overlay behind the 
text. Something with low priority that should not disturb face text 
properties, like those that for example hi-lock put on the text.

Since both the overlay I use and the faces normally used by hi-lock use 
background colors it just is not possible to use hi-lock when you have 
an overlay with a background color.

I suggest that we use overlay negative priority to let the overlay's 
faces have lower priority then text property faces. Would that be a good 
use?