anchor.diff:  
     // Format as RFC 1123 date.
     static String formatDate(Date date) {
  -    List wkday = ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"];
  -    List month = ["Jan", "Feb", "Mar", "Apr", "May", "Jun",
  -                  "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"];
  +    const List wkday = const ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"];
  +    const List month = const ["Jan", "Feb", "Mar", "Apr", "May", "Jun",
  +                              "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"];
   
       Date d = date.toUtc();
       StringBuffer sb = new StringBuffer();
  
positive.code: 
    static Date parseDate(String date) {
      final int SP = 32;
      List wkdays = ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"];
      List weekdays = ["Monday", "Tuesday", "Wednesday", "Thursday",
                       "Friday", "Saturday", "Sunday"];
      List months = ["Jan", "Feb", "Mar", "Apr", "May", "Jun",
                     "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"];
      List wkdaysLowerCase = ["mon", "tue", "wed", "thu", "fri", "sat", "sun"];
      List weekdaysLowerCase = ["monday", "tuesday", "wednesday", "thursday",
                                "friday", "saturday", "sunday"];
      List monthsLowerCase = ["jan", "feb", "mar", "apr", "may", "jun",
                              "jul", "aug", "sep", "oct", "nov", "dec"];
  
      final int formatRfc1123 = 0;
      final int formatRfc850 = 1;
  
negative.code:     }
  
      if (timeStr === null || dayOfMonthStr === null ||
          monthStr === null || yearStr === null) {
        error();
      }
  
      int year = toInt(yearStr);
      if (year >= 70 && year <= 99) year += 1900;
  