OptionalCostexpressIds of IfcPhysicalQuantity entities, in order. Absent writes $;
an empty array is rejected.
OptionalCostexpressIds of IfcCostValue / IfcAppliedValue entities, in the order they
must appear. Absent (undefined) writes $; an empty array is rejected.
OptionalDescriptionOptionalIdentificationOptionalObjectOptionalPredefined
IfcCostItem.