IfcSplitterGroupsEvent
Payload of IfcSplitter.onSplitsResolved, fired once split knows
what goes into each output file and before any file is written.
Properties
data
data:
GroupData[]
One entry per non-empty group, ascending by GroupData.groupId.
A split into more groups than there are element clusters simply yields
fewer entries than numGroups — use groupId to correlate, not the index.