163  *        Example output: "P12DT1M5.5S"
166 std::string toDurationString(std::chrono::milliseconds ms)  in toDurationString()  argument
168     if (ms < std::chrono::milliseconds::zero())  in toDurationString()
173     std::chrono::days days = std::chrono::floor<std::chrono::days>(ms);  in toDurationString()
174     ms -= days;  in toDurationString()
176     std::chrono::hours hours = std::chrono::floor<std::chrono::hours>(ms);  in toDurationString()
177     ms -= hours;  in toDurationString()
179     std::chrono::minutes minutes = std::chrono::floor<std::chrono::minutes>(ms);  in toDurationString()
180     ms -= minutes;  in toDurationString()
182     std::chrono::seconds seconds = std::chrono::floor<std::chrono::seconds>(ms);  in toDurationString()
183     ms -= seconds;  in toDurationString()
200     if (seconds.count() != 0 || ms.count() != 0)  in toDurationString()
202         secStr = std::format("{}.{:03}S", seconds.count(), ms.count());  in toDurationString()
251     unsigned mp = (5 * doy + 2) / 153;                      // [0, 11]  in civilFromDays()
252     unsigned d = doy - (153 * mp + 2) / 5 + 1;              // [1, 31]  in civilFromDays()