code: void onOk() {
  
          if (!m_selectionHandlers.isEmpty()) {
              Collection<CmsCategory> categories = m_tree.getSelectedCategories();
              for (I_CmsSelectionHandler<Collection<CmsCategory>> handler : m_selectionHandlers) {
                  handler.onSelection(categories);
              }
          }
      }
docs: On OK click.<p>