docs: void fillFromRight()
    {
      int gapWid = width() - population();
      int gidx = population();
      GBSNode p = rightChild();
      for (int j = 0; j < gapWid; j++)
        _nodeKey[j+gidx] = p._nodeKey[j];
      int delta = gapWid;
      if (p._population < delta)
        delta = p._population;
      _population   += delta;
      p._population -= delta;
      for (int j = 0; j < gidx; j++)
        p._nodeKey[j] = p._nodeKey[j+gapWid];
    }