From OpenSCADAWiki
Any object that has the need to provide dynamic access to itself or its components, must be inherited from the object of the dynamic tree node #TCntrNode. This relationship is automatically includes the node into the dynamic tree of objects covered by both — the direct and the reverse links, and also provides an opportunity to create containers for its own child nodes. In addition to this, the node is able to preact the inclusion and exclusion/removing of the node from the tree with the possibility of reject from the exclusion/removal.