* Adds a mouse down handler to activate the editing widget.<p>
*/
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 (!DomUtil.checkPositionInside(m_buttonBar.getElement(), event.getClientX(), event.getClientY())) {