Draw line between reference point of object and its parent

[Urs Liska]

Hi,

this post
http://www.sibeliusblog.com/tips/constrain-attachment-points-in-sibelius-and-finale/
lets me think if such a visualization might not be a good thing to have 
in Frescobaldi's Layout Control Options (and as a snippet in the 
openLilyLib repository).

What this would mean is:
- draw a red dot at a grob's ref-point (as we already have available)
- draw a red (or different?) dot at a grob's "owner"'s (is that right)
  ref-point.
  (I'm not completely sure if it's clear which grobs are applicable
   for that. It makes sense for objects that are "attached" to others
   such as an articulation or dynamic text is to a note. But we don't
   need note->staff or stem->notehead etc.
- draw a dashed (grey) line between them.

Does that look possible (OK, it's surely possible. Does that look feasible)?
Is anybody interested in giving it a shot?

--
Urs Liska
www.openlilylib.org