code: def clear(self) -> None:
          
          # these internal records are used as a way to tell the difference between
          # changes that came before and after the clear
          self.record_changeset()
          self._clears_at.add(self.latest_id)
          self.record_changeset()
docs: Treat as if the *underlying* database will also be cleared by some other mechanism.
          We build a special empty changeset just for marking that all previous data should
          be ignored.