public ElementId ReferenceElementId { get; }

Public ReadOnly Property ReferenceElementId As ElementId
	Get

public:
property ElementId^ ReferenceElementId {
	ElementId^ get ();
}

A MassSurfaceData may represent multiple faces from the same or different elements. This generally only happens if the faces are geometrically fully coincident and logically represent a single building object. "Interior walls" of the conceptual energy building model is a common example where two different faces may be represented by a single MassSurfaceData.