title: drag event for jquery-ui-sortable
body: <p>How to listen to <code>drag</code> event when a <code>jquery-ui-sortable</code> is being dragged?</p>
  
  <p>By hit-n-trial strategy, I've tried <code>drag</code> event from <code>jquery-ui-draggable</code> but it's not working.</p>
  
  <pre><code>$('.widget_container').sortable({
      drag: function(event, ui) { console.log('drag'); }
  });
  </code></pre>