code: private void overButtonBar(Widget buttonBar) {
  
          if ((m_buttonBar == null) || (buttonBar.getElement() != m_buttonBar.getElement())) {
              closeAll();
              m_buttonBar = buttonBar;
              setButtonBarVisibility(m_buttonBar, true);
          }
      }
docs: Handles the mouse over event for a button bar.<p>
  
  @param buttonBar the event source