Anchoring markups

[Bertalan Fodor (LilyPondTool)]

I think there is a general problem in LilyPond with the positioning of 
things.
You can easily attach a markup (that now actually can contain anything) 
to a note. But can't attach it to a clef, a stem, a bar line etc.
It would be very good, if you could attach a markup to any grob.
I suppose it wouldn't be very hard, but I wonder if more experienced 
users could tell me what to do.
I'm thinking about something like this:

\clef c ^\markup { }

Syntax-wise it may be difficult. But wouldn't it be possible to create 
music function that takes a grob name, and changes the drawing function 
in a way that you can put a markup above, below, left or right to it?

Bert