code: private void evalDateTime(MessageArg arg) {
      if (!arg.resolve()) {
        return;
      }
      
      initCalendarArgsParser();
      parseArgs(calendarArgsParser);
      
      ZonedDateTime datetime = parseDateTime(arg);
      CalendarFormatter formatter = CLDR_INSTANCE.getCalendarFormatter(locale);
      formatter.format(datetime, calendarArgsParser.options(), buf);
    }
docs: DATETIME - Evaluate the argument as a datetime, with options specified as key=value.