anchor.diff:    /// Use the [intl](http://pub.dartlang.org/packages/intl) package
     /// at the pub shared packages repo.
     String toString() {
  +    var offset = _timeZone.offset;
  +
       String y = _fourDigits(year);
       String m = _twoDigits(month);
       String d = _twoDigits(day);
  
positive.code:     if (isUtc) {
        return "$y-$m-${d}T$h:$min:$sec.${ms}Z";
      } else {
        return "$y-$m-${d}T$h:$min:$sec.$ms";
      }
    }
  
  
negative.code:     String min = _twoDigits(minute);
      String sec = _twoDigits(second);
      String ms = _threeDigits(millisecond);
  
      if (isUtc || offset == 0) {
        return "$y-$m-$d $h:$min:$sec.${ms}Z";
      } else {
        String offSign = offset.sign > 0 ? '+' : '-';
        offset = offset.abs() ~/ 1000;
        String offH = _twoDigits(offset ~/ 3600);
        String offM = _twoDigits(offset % 60);
  
        return "$y-$m-$d $h:$min:$sec.$ms$offSign$offH$offM";
      }
    }
  
  