code: protected void visitChildren(ParentNode<? extends N> node) {
      List<? extends N> children = node.getChildren();
      int size = children.size();
      for (int i = 0; i < size; i++) {
        visit(children.get(i));
      }
    }
docs: Helper to visit all the children of a node, in order.
  
  @param node The parent node whose children to visit.
  @see #visitChildrenAllowingConcurrentModification