visualizing grob ancestry

[Mark Polesky]

Does a grob-type always have the same set of parent-types?

For example, does an Accidental grob always have X-parent
AccidentalPlacement and Y-parent NoteHead? If so, could this
information be incororated into the IR? It took me a while
before I was able to figure this sort of thing out:

        ________________System__________________
       |    |  |                   |            |
       |    |  |                   |            |
       |    |  NonMusicalPaperColumn            |
       |    |       \          \                |
       |    |        \          VerticalAlignment
        \    \        \                 /
         PaperColumn   VerticalAxisGroup
        /           \ /            /
       /             X            /
      /             / \          /
     /             /   NoteColumn
     \            /    /        \
AccidentalPlacement   |          |
              \        \        /
               \        NoteHead
                \          /
                 Accidental


And that's the ancestry for just one grob!

I assume that a comprehensive visual "parent-web" demonstrating
all such relationships would be too convoluted to have any
practical value, and too difficult to generate to even justify
trying such a thing (although I've seen some impressive examples,
like http://www.visualthesaurus.com/). But, I imagine it should be
(at the very least) possible to have something like this near the
top of each node within IR 3.1 All layout objects:

   X and Y parents: AccidentalPlacement and NoteHead.

But I don't know if the parents can change in different contexts.
If not, then does anyone have an idea how this could be generated?

Thanks.
- Mark