[ospanstream.swap]
31 Input/output library [input.output]
31.9 Span-based streams [span.streams]
31.9.5 Class template basic_ospanstream [ospanstream]
31.9.5.3 Swap [ospanstream.swap]
void swap(basic_ospanstream& rhs);
template<class charT, class traits>
void swap(basic_ospanstream<charT, traits>& x, basic_ospanstream<charT, traits>& y);