Attaching an alist to a grob

[Urs Liska]

Hi list,

I'm working on a music function/engraver combination. The music function 
has to attach information to a grob to pass it on to the engraver.

I found that an alist is the appropriate data type for the information, 
so I need a way to attach an alist to a grob in a music function. I made 
it to work smoothly, but I'm quite positive that hijacking the 'details 
property for that purpose is completely inacceptable.

One problem is that the function doesn't necessarily take a ly:music? 
argument but can also work on the grob name and issue a \once \override 
command, so I don't see a chance to get hold of the grob and at least 
append my alist to 'details (which I suppose wouldn't hurt LilyPond).

So does anyone have an idea how I can attach an alist to a grob so that 
an engraver can retrieve it?
Is it for example possible to add an arbitrary property to a grob?

TIA
Urs