anchor.diff:  
   /// Days in a month. This array uses 1-based month numbers, i.e. January is
   /// the 1-st element in the array, not the 0-th.
  -const _DAYS_IN_MONTH =
  -    const [ 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 ];
  -
  -int _daysInMonth(int year, int month) => (month == DateTime.FEBRUARY &&
  -    _isLeapYear(year)) ? 29 : _DAYS_IN_MONTH[month];
  +const _DAYS_IN_MONTH = const [
  +  0,
  +  31,
  +  28,
  +  31,
  +  30,
  +  31,
  +  30,
  +  31,
  +  31,
  +  30,
  +  31,
  +  30,
  +  31
  +];
  +
  +int _daysInMonth(int year, int month) =>
  +    (month == DateTime.FEBRUARY && _isLeapYear(year))
  +        ? 29
  +        : _DAYS_IN_MONTH[month];
   
   bool _isLeapYear(int year) =>
       (year % 4 == 0) && ((year % 100 != 0) || (year % 400 == 0));
  
positive.code:   /// Returns the point in time that's given amount of time ago. The
    /// amount of time is the sum of individual parts. Parts are compatible with
    /// ones defined in [Duration].
    DateTime ago({int days: 0, int hours: 0, int minutes: 0, int seconds: 0,
        int milliseconds: 0, int microseconds: 0}) => agoBy(new Duration(
            days: days,
            hours: hours,
            minutes: minutes,
  
negative.code:   /// Returns the point in time that's given amount of time from now. The
    /// amount of time is the sum of individual parts. Parts are compatible with
    /// ones defined in [Duration].
    DateTime fromNow(
            {int days: 0,
            int hours: 0,
            int minutes: 0,
            int seconds: 0,
            int milliseconds: 0,
            int microseconds: 0}) =>
        fromNowBy(new Duration(
            days: days,
            hours: hours,
            minutes: minutes,
  