false for a dry run.
Every original with its copy, in creation order.
OptionalcopyThe product's copy; undefined for an append.
Existing relationships and layers the copies joined.
Append: copies given a new GlobalId.
Append: source entities this model already holds, with the one used.
Relationships of an original the copies do not get.
What
IfcModel.copyProductorIfcModel.appenddid, or, for a dry run, would do.