see how defcon is managing his representation factories: RoboFont uses a subclass to build the glyph cells see http://code.typesupply.com/browser/packages/defconAppKit/trunk/Lib/defconAppKit/representationFactories/glyphCellFactory.py use addRepresentationFactory to register a new one see http://code.typesupply.com/browser/packages/defcon/trunk/Lib/defcon/objects/glyph.py#L8 good luck