docs: @SuppressWarnings("unlikely-arg-type")
  	@Pure
  	public int indexOf(P element) {
  		int idx = 0;
  		for (final GridCellElement<P> e : this.elements) {
  			if (e.isReferenceCell(this)) {
  				if (e.equals(element)) {
  					return idx;
  				}
  				++idx;
  			}
  		}
  		return -1;
  	}