Converts this content into its strict counterpart.
(general: StringAdd).self
(general: StringFormat).self
(general: ArrowAssoc[General]).x
(Since version 2.10.0) Use leftOfArrow
instead
(general: Ensuring[General]).x
(Since version 2.10.0) Use resultOfEnsuring
instead
Basic model for multipart content as defined by http://tools.ietf.org/html/rfc2046.