'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.'

@classmethod
def _create_outerjoin(cls, left, right, onclause=None):

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