Is that a thing anybody wants?

I've written some (admittedly crude) patches that do the very basics; doing it right would be considerably more work (lots of little things like making sure you can't have two selections, eliminating duplicated decorations, etc.).

Somebody asked for a screen shot of the usages tree view - that's it on the left (sorry about the resolution, I haven't got anything decent for picture editing for windows on my laptop).