public static string ToXsdTimeSpanString(TimeSpan timeSpan)
        {
#if    PLATFORM_USE_XML_DLL
            var r = XmlConvert.ToString(timeSpan);
#if __MonoCS__
            // Mono returns DT even if time is 00:00:00
            if (r.EndsWith("DT"))
            {
                return(r.Substring(0, r.Length - 1));
            }
#endif
            return(r);
#else
            XsdDuration duration = new XsdDuration(timeSpan);

            return(duration.ToString( ));
#endif
        }