code: public boolean addCellLink(GridCell<P> cell) {
  		if (this.cells.add(cell)) {
  			return isReferenceCell(cell);
  		}
  		return false;
  	}
docs: Add a reference from this element to a cell that is containing this element.
  
  @param cell the grid cell.
  @return <code>true</code> if the added cell is the reference;
  <code>false</code> if the added cell is not the reference.