TODO
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NOTE: nested enums are broken do to dynamic binning.
Don't rebuild entire bplane when bbox grows.
unsubbing sometimes.
Some (remaining) bplane design issues:
groups?
idea: support small number of groups by having
separate bplane for each group. Do selection this
way. Logically layered on top of bplanes - but may
want to integrate.
DECISION: defer for now.
pack/unpack?
Seems incompatible with user alloc/dealloc.
Complicated.
DECISION: Forget it.
coarse/fine with cache.
can be added later. should fit in nicely.
no special support needed.
integrated find/add?
can add later.
don't worry about it now.
May want to add attributes, via external hash.
69df88520c