@classmethod
def _create_outerjoin(cls, left, right, onclause=None, full=False):
    """Return an ``OUTER JOIN`` clause element.

        The returned object is an instance of :class:`.Join`.

        Similar functionality is also available via the
        :meth:`~.FromClause.outerjoin()` method on any
        :class:`.FromClause`.

        :param left: The left side of the join.

        :param right: The right side of the join.

        :param onclause:  Optional criterion for the ``ON`` clause, is
          derived from foreign key relationships established between
          left and right otherwise.

        To chain joins together, use the :meth:`.FromClause.join` or
        :meth:`.FromClause.outerjoin` methods on the resulting
        :class:`.Join` object.

        """
    return cls(left, right, onclause, isouter=True, full=full)
