anchor.diff:    void addSlice(List<int> data, int start, int end, bool isLast) {
       if (_closed) return;
       if (start < 0 || start > data.length) {
  -      throw ArgumentError("Invalid start position");
  +      throw new ArgumentError("Invalid start position");
       }
       if (end < 0 || end > data.length || end < start) {
  -      throw ArgumentError("Invalid end position");
  +      throw new ArgumentError("Invalid end position");
       }
       try {
         _empty = false;
  
positive.code:   /**
     * Get a [Converter] for encoding to `GZip` compressed data.
     */
    final Converter<List<int>, List<int>> encoder =
        const ZLibEncoder(gzip: true, level: level);
  
    /**
     * Get a [Converter] for decoding `GZip` compressed data.
     */
    final Converter<List<int>, List<int>> decoder = const ZLibDecoder();
  
    /**
     * The compression-[level] can be set in the range of `1..10`, with `6` being
  
negative.code: 
    void addSlice(List<int> chunk, int start, int end, bool isLast) {
      if (chunk is Uint8List) {
        var list = chunk as Uint8List;
        builder.add(new Uint8List.view(list.buffer, start, end - start));
      } else {
        builder.add(chunk.sublist(start, end));
      }
    }
  
  