code: private void leftShift(
      int           ix)
    {
      for (int j = 0; j < ix; j++)
        _nodeKey[j] = _nodeKey[j+1];
    }
docs: Open up a slot in a node by shifting the keys left.
  
  <p>We are inserting a new key into a node that is not currently
  full.  There is at least one vacant slot.  We open up the correct
  slot for the new key by shifting all other keys left.</p>