anchor.diff:        message != null ? message : '$start..$stop expected');
   }
   
  -class _RangeCharPredicate extends CharacterPredicate {
  -
  -  final int _start;
  -
  -  final int _stop;
  -
  -  const _RangeCharPredicate(this._start, this._stop);
  -
  -  @override
  -  bool test(int value) => _start <= value && value <= _stop;
  +class _RangeCharPredicate implements CharacterPredicate {
  +
  +  final int start;
  +  final int stop;
  +
  +  const _RangeCharPredicate(this.start, this.stop);
  +
  +  @override
  +  bool test(int value) => start <= value && value <= stop;
   
   }
   
  
positive.code:       message != null ? message : 'digit expected');
  }
  
  class _DigitCharPredicate extends CharacterPredicate {
  
    const _DigitCharPredicate();
  
  
negative.code:     return false;
    }
  
  }
  
  int _toCharCode(element) {
  