false for a dry run or an unchanged unit.
When the area unit followed the length unit.
Entities created, or for a dry run the ids the commit will create.
The project length unit before, as named (MILLI METRE, foot).
The new length unit entity; undefined when nothing changes.
Entities removed, or for a dry run planned for removal.
What
IfcModel.convertLengthUnitdid, or, for a dry run, would do.