[ostream.assign]
31 Input/output library [input.output]
31.7 Formatting and manipulators [iostream.format]
31.7.6 Output streams [output.streams]
31.7.6.2 Class template basic_ostream [ostream]
31.7.6.2.3 Assignment and swap [ostream.assign]
basic_ostream& operator=(basic_ostream&& rhs);
void swap(basic_ostream& rhs);