anchor.diff:          return new Interval(start, end);
         });
   }
  +
  +
   
   /// Convert a month token to a month value.
   int _toMonth(String m) {
  
positive.code:   dayToken() => token(digit().repeat(1, 2));
    monthToken() => token(letter().repeat(3, 9));
    yearToken() => token(digit().repeat(2, 4));
    quarterToken() => token(char('Q') & digit() & char(',')) & yearToken();
  }
  
  /// Parse a term
  
negative.code: 
  import 'package:petitparser/petitparser.dart';
  import 'package:date/date.dart';
  import 'package:timezone/timezone.dart';
  
  Set<String> _mon = new Set.from([
    'Jan',
  