code: void openWindow() {
  
          if (m_dialogWindow == null) {
              m_dialogWindow = CmsBasicDialog.prepareWindow(DialogWidth.wide);
              m_dialogWindow.setCaption("Select categories");
          }
          if (m_dialog == null) {
              m_dialog = new CmsCategorySelectDialog("/");
              m_dialogWindow.setContent(m_dialog);
              m_dialog.addSelectionHandler(this);
          }
          A_CmsUI.get().addWindow(m_dialogWindow);
          m_dialogWindow.center();
          m_dialog.setSelectedCategories(m_tree.getSelectedCategories());
      }
docs: Opens the select window.<p>