I think that transportUnitLevel has to be required when unitReferences are used.
transportUnitLevel can still be optional in units
When unitreferences are used, then there is need to know if the unit is standing on the referenced unit or if the referenced unit is standing on the unit.
I think that
transportUnitLevelhas to be required whenunitReferencesare used.transportUnitLevelcan still be optional inunitsWhen
unitreferencesare used, then there is need to know if the unit is standing on the referenced unit or if the referenced unit is standing on the unit.