nise this object's state with that
        fact.

        XXX: this docstring is duplicated in many places, e.g. lockable_files.py

        Args:
          token: if this is already locked, then lock_write will fail
            unless the token matches the existing lock.
        Returns:
          a token if this instance supports tokens, otherwise None.

        Raises:
          TokenLockingNotSupported: when a token is given but this
            instance doesn't support using token locks.
          MismatchedToken: if the specified token doesn't match the token
            of the existing lock.

        Returns:
          A RepositoryWriteLockResult.
        )