title: Dropping onto an event (as opposed to the calendar) - how to identify event?
body: <p>I have successfully implemented dragging of a jquery-ui element onto my fullCalendar. The problem is that what I want to drop onto is not the calendar itself but a specific event displayed on the calendar in order to add the dropped item to the event. The missing piece is how to identify the event that was under the mouse when I dropped.</p>
  
  <pre><code>drop: function (date, allDay, jsEvent, ui)
  {
     var event = ???;
     event.description += ui.helper.data("filters").text;
     $('#calendar').fullCalendar('updateEvent', event);
  }
  </code></pre>