System.DateTimeParse.ExpandPredefinedFormat C# (CSharp) Method

        private static String ExpandPredefinedFormat(String format, ref DateTimeFormatInfo dtfi, ref ParsingInfo parseInfo, ref DateTimeResult result) {
            //
            // Check the format to see if we need to override the dtfi to be InvariantInfo,
            // and see if we need to set up the userUniversalTime flag.
            //
            switch (format[0]) {
                case 'o':
                case 'O':       // Round Trip Format
                    parseInfo.calendar = GregorianCalendar.GetDefaultInstance();
                    dtfi = DateTimeFormatInfo.InvariantInfo;
                    break;
                case 'r':
                case 'R':       // RFC 1123 Standard.  (in Universal time)
                    parseInfo.calendar = GregorianCalendar.GetDefaultInstance();
                    dtfi = DateTimeFormatInfo.InvariantInfo;
                    break;
                case 's':       // Sortable format (in local time)
                    dtfi = DateTimeFormatInfo.InvariantInfo;
                    parseInfo.calendar = GregorianCalendar.GetDefaultInstance();
                    break;
                case 'u':       // Universal time format in sortable format.
                    parseInfo.calendar = GregorianCalendar.GetDefaultInstance();
                    dtfi = DateTimeFormatInfo.InvariantInfo;
                    break;
                case 'U':       // Universal time format with culture-dependent format.
                    parseInfo.calendar = GregorianCalendar.GetDefaultInstance();
                    result.flags |= ParseFlags.TimeZoneUsed;
                    result.timeZoneOffset = new TimeSpan(0);
                    result.flags |= ParseFlags.TimeZoneUtc;
                    if (dtfi.Calendar.GetType() != typeof(GregorianCalendar)) {
                        dtfi = (DateTimeFormatInfo)dtfi.Clone();
                        dtfi.Calendar = GregorianCalendar.GetDefaultInstance();
                    }
                    break;
            }

            //
            // Expand the pre-defined format character to the real format from DateTimeFormatInfo.
            //
            return (DateTimeFormat.GetRealFormat(format, dtfi));
        }