title: Should I emit QAbstractItemModel dataChanged for parent node only in a tree model
body: <p>I am writing a QAbstractItemModel representing a tree.</p>
  <p>After several tests, I noticed that, when dataChanged is emitted for a parent node, an attached QTreeView will also refresh all children of that node. While I expected that dataChanged should have been also emitted for all underlying children whose data was modified.</p>
  <p>I can't find explicit details in the documentation.</p>
  <p>Should I:</p>
  <ul>
  <li>Emit dataChanged only for the parent node, and all child nodes will be updated?</li>
  <li>Emit dataChanged for all modified children as well, in that case the observed behavior is just a lack of optimization from QTreeView</li>
  </ul>