docs: private void initNestedContainers() {
  
          for (CmsContainer container : m_controller.getContainers().values()) {
              if (container.isSubContainer()) {
                  CmsContainerPageContainer containerWidget = m_controller.m_targetContainers.get(container.getName());
                  // check if the sub container is a valid drop targets
                  if (m_dragInfos.keySet().contains(containerWidget)) {
                      CmsContainer parentContainer = m_controller.getContainers().get(container.getParentContainerName());
                      // add the container to all it's ancestors as a dnd child
                      while (parentContainer != null) {
                          if (m_dragInfos.keySet().contains(
                              m_controller.m_targetContainers.get(parentContainer.getName()))) {
                              m_controller.m_targetContainers.get(parentContainer.getName()).addDndChild(containerWidget);
                          }
                          if (parentContainer.isSubContainer()) {
                              parentContainer = m_controller.getContainers().get(
                                  parentContainer.getParentContainerName());
                          } else {
                              parentContainer = null;
                          }
                      }
                  }
              }
  
          }
      }