docs: def _init_metadata(self):
          """stub"""
          self._file_metadata = {
              'element_id': Id(self.my_osid_object_form._authority,
                               self.my_osid_object_form._namespace,
                               'file'),
              'element_label': 'File',
              'instructions': 'accepts an asset id and optional asset_content type',
              'required': False,
              'read_only': False,
              'linked': False,
              'array': False,
              'default_object_values': [{}],
              'syntax': 'OBJECT',
              'object_set': []
          }