[mkgmap-dev] Multipolygon/boundary relations and subrelations

Today I observed that the boundary relation of Luxembourg was changed in a way that it does not contain the boundary ways itself but links to other relations that contain parts of the boundary (Luxembourg/Belgium; Luxembourg/Netherlands etc.). I am not sure if that's an accepted scheme for mps/boundaries. Does anyone know if that's correct and accepted? Should mkgmap support this? WanMil