anchor.diff:        case 'u':
           int remainingLength = _json.length - _index;
           if (remainingLength >= 4) {
  -          var hexString = _json.substring(_index + 1, _index + 5);
  +          var hexString = _json.substring(_index, _index + 4);
             _index += 4;
             var hexInt = int.parse(hexString, radix: 16);
             return UTF8.decode([hexInt]);
  
positive.code:   String _parseEscapedStringFragment() {
      _index++;
      String character = _json[_index];
      switch (character) {
        case '"':
        case r'\':
  
negative.code:         string += _parseEscapedStringFragment();
        } else {
          string += character;
          _index++;
        }
        if (_index == _json.length) {
          throw new LexerException("Invalid json fragment encountered: $string");
        }
  