docs: def rollforward(self):
          """Restore a reverted modification to the refpkg.
          """
          if self.contents['rollforward'] is None:
              raise ValueError("No operation to roll forward on refpkg")
          new_log_message = self.contents['rollforward'][0]
          new_contents = self.contents['rollforward'][1]
          new_contents['log'] = [new_log_message] + self.contents.pop('log')
          self.contents['rollforward'] = None
          new_contents['rollback'] = copy.deepcopy(self.contents)
          new_contents['rollback'].pop('rollforward')
          self.contents = new_contents
          self._sync_to_disk()