or …, IFCVIBRATIONISOLATORTYPEENUM(.SPRING.), … vs. …, .SPRING., …
it should be a recoverable error in an P21 parser. I would see the effort of handling the compatibility issue minor to the overload, when introducing two new classes and deprecating two others.
attached is a 2011 MSG document discussing backward compatibility at the level of P21 files. According to it, we should accept the change to a select type.20110702_IFC4_SchemaCompatibilityAssessment.pdf (149.2 KB)