The ISO 8601 format string

        /// <summary>
        /// The ISO 8601 format string.
        /// </summary>

        private const string Iso8601Format = "yyyy'-'MM'-'dd'T'HH':'mm':'ss'Z'";
        
        //SortableDateTimePattern (ISO 8601)
        public static string ToIso8601(DateTime value)
        {
            return value.ToUniversalTime().ToString(Iso8601Format, CultureInfo.InvariantCulture);            
        }

        public static DateTime ParseIso8601(string value)
        {
            return DateTime.ParseExact(value,
                Iso8601Format, CultureInfo.InvariantCulture,
                    DateTimeStyles.AssumeUniversal | DateTimeStyles.AdjustToUniversal);
        }