Access/address arbitrary grobs' coordinates from event function

[Urs Liska]

Hi all,

in order to improve the multi-segment slurs I would like to know if it
is possible to get information about arbitrary grobs from within an
event function.

Concretely I would like to know if there's a way to get hold of the
coordinates (anchor points) of an arbitrary other grob from within a
function defined as "define-event-function".

I would like to somehow "tag" the other grob in the input file in order
to get and keep some kind of "handle" to it and then access its
coordinates in an event function. The idea is to be able to define the
inflection point of a multi-segment slur relative to one or more other
items on the page. For example between two notes. Anchoring such complex
slurs on other items like notes or stems or beams will significantly
increase the chance that changes in layout may keep the slur intact.

My question is: is there a way to get the necessary information at the
right processing stage. I see that when saving some values in a music-
or scheme-function this is available in the event-function of the
compound slur. But probably it's not possible to retrieve the
positioning data at that point yet.

Any pointers?

TIA
Urs