docs: public void flip(final int x) {
      final short hb = BufferUtil.highbits(x);
      final int i = highLowContainer.getIndex(hb);
      if (i >= 0) {
        MappeableContainer c = highLowContainer.getContainerAtIndex(i);
        c = c.flip(BufferUtil.lowbits(x));
        if (!c.isEmpty()) {
          ((MutableRoaringArray) highLowContainer).setContainerAtIndex(i, c);
        } else {
          ((MutableRoaringArray) highLowContainer).removeAtIndex(i);
        }
      } else {
        final MappeableArrayContainer newac = new MappeableArrayContainer();
        ((MutableRoaringArray) highLowContainer).insertNewKeyValueAt(-i - 1, hb,
            newac.add(BufferUtil.lowbits(x)));
      }
    }