title: GWT Event Preview vs Event Handler
body: <p>My question is, what's the different between event preview and event handler in GWT. </p>
  
  <p>There is a callback function <code>boolean onEventPreview(Event event)</code> for event preview and a callback function <code>void onBrowserEvent(Event event)</code> as well. They are pretty similar, so what's the different between them? Especially when should I use the event preview at all when the event handler works perfect?</p>
  
  <p>thanks</p>