code: def _register_make(cls):
      '''class decorator to Register mf make'''
      assert cls.nxm_headers is not None
      assert cls.nxm_headers is not []
      for nxm_header in cls.nxm_headers:
          assert nxm_header not in _MF_FIELDS
          _MF_FIELDS[nxm_header] = cls.make
      return clf _register_make(cls):
      '''class decorator to Register mf make'''
      assert cls.nxm_headers is not None
      assert cls.nxm_headers is not []
      for nxm_header in cls.nxm_headers:
          assert nxm_header not in _MF_FIELDS
          _MF_FIELDS[nxm_header] = cls.make
      return cls
docs: class decorator to Register mf make