internal static string Serialize(OrdinalDateTimeDuration dateTimeDuration, ISO8601Options options)
        {
            if (options == null)
            {
                options = ISO8601Options.Default;
            }

            return dateTimeDuration.DateDuration.ToString(options) + dateTimeDuration.TimeDuration.ToString(options).Substring(1);
        }
 internal static CalendarDateTimeDuration ToCalendarDateTimeDuration(OrdinalDateTimeDuration duration)
 {
     return new CalendarDateTimeDuration(duration.DateDuration.ToCalendarDateDuration(), duration.TimeDuration);
 }