boost::text::v1::stream_safe_copy
// In header: <boost/text/stream_safe.hpp> template<code_point_iter I, std::sentinel_for< I > S, std::weakly_incrementable O> constexpr copy_result< I, O > stream_safe_copy(I first, S last, O out);
Writes sequence [first, last) to out, ensuring Stream-Safe Text Format.
See Also:
https://unicode.org/reports/tr15/#Stream_Safe_Text_Format