title: Undo/Redo in QTextEdit
body: <p>A program I am creating includes a <code>QTextEdit</code> part. I want to perform the following feature:</p>
  
  <ol>
  <li><p>When I try to press on a <code>QAction</code> item playing a role of <strong>Undo</strong> then
  when the end of the track history of <strong>Undo</strong> will be achieved <strong>the concrete value (either <code>bool</code> or <code>int</code>)</strong> must be returned. After the successful execution of that (the above command) as I guess another commands will be implemented.</p></li>
  <li><p>The same things must be performed for <strong>Redo</strong>.</p></li>
  </ol>
  
  <p>Thank you.</p>