code: def heading(self):
          
          if self._heading is None:
              self._heading = Heading()  # instance-level heading
          if not self._heading:  # lazy loading of heading
              if self.connection is None:
                  raise DataJointError(
                      'DataJoint class is missing a database connection. '
                      'Missing schema decorator on the class? (e.g. @schema)')
              else:
                  self._heading.init_from_database(self.connection, self.database, self.table_name)
          return self._heading
docs: Returns the table heading. If the table is not declared, attempts to declare it and return heading.
          :return: table heading