docs: private void calcNoOfNodes(Node node) {
          if (node instanceof Parent) {
              if (((Parent) node).getChildrenUnmodifiable().size() != 0) {
                  ObservableList<Node> tempChildren = ((Parent) node).getChildrenUnmodifiable();
                  noOfNodes += tempChildren.size();
                  for (Node n : tempChildren) { calcNoOfNodes(n); }
              }
          }
      }