[iostream.assign]
31 Input/output library [input.output]
31.7 Formatting and manipulators [iostream.format]
31.7.5 Input streams [input.streams]
31.7.5.7 Class template basic_iostream [iostreamclass]
31.7.5.7.4 Assignment and swap [iostream.assign]
basic_iostream& operator=(basic_iostream&& rhs);
void swap(basic_iostream& rhs);