docs: protected void appendCopy(PointableRoaringArray highLowContainer, int startingIndex, int end) {
      extendArray(end - startingIndex);
      for (int i = startingIndex; i < end; ++i) {
        this.keys[this.size] = highLowContainer.getKeyAtIndex(i);
        this.values[this.size] = highLowContainer.getContainerAtIndex(i).clone();
        this.size++;
      }
    }