title: How to programmatically fire keydown event in ExtJS 4
body: <p>In ExtJs 4 how can I programmatically fire 'keydown' (or 'keypress') event (on TAB key) ?
  I should want to simulate a TAB key pression in response to another event.
  I have tried with code (in this event handler) :</p>
  
  <pre><code>field.fireEvent('keydown', {keyCode: 9})
  </code></pre>
  
  <p>but it's not working...</p>