- The ``version_id_generator`` parameter of ``Mapper`` can now be specified
to rely upon server generated version identifiers, using triggers
or other database-provided versioning features, by passing the value
``False``.  The ORM will use RETURNING when available to immediately
load the new version identifier, else it will emit a second SELECT.
[ticket:2793]
- Added a new variant to :meth:`.ValuesBase.returning` called
:meth:`.ValuesBase.return_defaults`; this allows arbitrary columns
to be added to the RETURNING clause of the statement without interfering
with the compilers usual "implicit returning" feature, which is used to
efficiently fetch newly generated primary key values.  For supporting
backends, a dictionary of all fetched values is present at
:attr:`.ResultProxy.returned_defaults`.
- wrote docs for version id feature overall [ticket:867]