The mimetype parameters as dict. For example if the
        content type is ``text/html; charset=utf-8`` the params would be
        ``{'charset': 'utf-8'}``.

        .. versionadded:: 0.5

def mimetype_params(self):
        """The mimetype parameters as dict. For example if the
        content type is ``text/html; charset=utf-8`` the params would be
        ``{'charset': 'utf-8'}``.

        .. versionadded:: 0.5
        """

        def on_update(d):
            self.headers["Content-Type"] = dump_options_header(self.mimetype, d)

        d = parse_options_header(self.headers.get("content-type", ""))[1]
        return CallbackDict(d, on_update)