docs: private Component createAddKeyButton() {
  
          // the "+" button
          Button addKeyButton = new Button();
          addKeyButton.addStyleName("icon-only");
          addKeyButton.addStyleName("borderless-colored");
          addKeyButton.setDescription(m_messages.key(Messages.GUI_ADD_KEY_0));
          addKeyButton.setIcon(FontOpenCms.CIRCLE_PLUS, m_messages.key(Messages.GUI_ADD_KEY_0));
          addKeyButton.addClickListener(new ClickListener() {
  
              private static final long serialVersionUID = 1L;
  
              public void buttonClick(ClickEvent event) {
  
                  handleAddKey();
  
              }
          });
          return addKeyButton;
      }