This is mentioned in https://wiki.openstreetmap.org/wiki/Guidelines_for_pedestrian_navigation#Ways_inside_buildings although it has other problems. Also used in https://wiki.openstreetmap.org/wiki/MENTZ_GmbH/Modellierungsvorschläge_Indoor and https://wiki.openstreetmap.org/wiki/France/Transilien/Hackcess in some extent. 