                   them. This is used when the message is being
                       serialized by a generator. Default: False.

message_factory     -- the class to use to create new message objects.
                       If the value is None, the default is Message.

verify_generated_headers
                    -- if true, the generator verifies that each header
                       they are properly folded, so that a parser won't
                       treat it as multiple headers, start-of-body, or
                       part of another header.
                       This is a check against custom Header & fold()
                       implementations.
Fr;