code: private void addActivationHandler() {
  
          if (m_activationHandlerRegistration == null) {
              m_activationHandlerRegistration = addMouseDownHandler(new MouseDownHandler() {
  
                  public void onMouseDown(MouseDownEvent event) {
  
                      // only act on click if not inside the button bar
                      if (!m_buttonBar.getElement().isOrHasChild((Node)event.getNativeEvent().getEventTarget().cast())) {
                          activateWidget();
                      }
                  }
              });
          }
      }
docs: Adds a mouse down handler to activate the editing widget.<p>