Doc'd for_save argument of Expression.resolve_expression().
@@ -944,6 +944,9 @@ calling the appropriate methods on the wrapped expression.
``summarize`` is a boolean that, when ``True``, signals that the
query being computed is a terminal aggregate query.
+ ``for_save`` is a boolean that, when ``True``, signals that the query
+ being executed is performing a create or update.
+
.. method:: get_source_expressions()
Returns an ordered list of inner expressions. For example::
