ed regions.</li>
    <li><code>onRemove(item, callback)</code> Fired when an item is about to be deleted. If not implemented, the item will be always removed.</li>
  </ul>

  <p>
    Each of the callbacks is invoked with two arguments:
  </p>
  <ul>
    <li><code>item</code>: the item being manipulated</li>
    <li><code>callback</code>: a callback function which must be invoked to report back. The callback must be invoked as <code>callback(item)</code> or <code>callback(null)</code>.
    Here, <code>item</