Groups in Picts

[Henry Lieberman <lieber@MEDIA-LAB.MEDIA.MIT.EDU>]

I am writing a Lisp interface to Mac Pict objects, and 
there is one thing I can't figure out from Inside Mac. 
Where is the information about groups?  If two graphic objects are
grouped [say in MacDraw], then transferred via the clipboard to 
some other application [say, Canvas, Fullwrite, etc.] that has a
group operation, the groups information is preserved. That seems to 
indicate that it resides in the Pict object.  However, I cannot
find any Pict opcode that has anything to do with grouping. Could it
perhaps be in the [uninterpreted] so-called "picture comments", and if 
so, is its format documented?  Or has anyone already done a Lisp/Pict 
interface?