title: Detecting a cancelled drag and drop action when uploading files
body: <p>This is the behavior I want:</p>
  
  <ol>
  <li>The user starts dragging a file from the file explorer</li>
  <li>When the file hovers over the browser window 3 drop zones appear</li>
  <li>When the user cancels the drag and drop or drops the file the drop zones disappear.</li>
  </ol>
  
  <p>The problem I'm having is with #3.<br>
  The drop zones appear fine when using the <code>dragenter</code> on <code>document</code> but I can't get them to disappear again.</p>
  
  <p>I've tried binding on <code>dragend</code> which never fires, <code>dragleave</code> which fires every time the the drag leaves a descendant so the drag area blinks.</p>
  
  <p>Which event would be the correct one to listen to?</p>