     <li>Cancel of processing (for example, user pressed Cancel button).</li>
    </ul>
    <p>Also, work of the library may cause two types of exceptional situations
      that require notification of the calling application:</p>
    <ul>
      <li>Memory shortage</li>
      <li>Data read error.</li>
    </ul>
    <p>An application may set its own callbacks that will be called in the cases
      mentioned above to notify the user (or the calling program).</p>
    <p><a name="progress"></a></p>
    <h4>Prog