w_progress stage</dt>
      <dd>Current processing stage. This number can be converted to string by
        call to <a href="#strprogress">LibRaw::strprogress</a>. Not all
        processing stages are covered by callback calls.</dd>
      <dt>int iteration</dt>
      <dd>Iteration number within current stage (from 0 to expected-1).</dd>
      <dt>int expected</dt>
      <dd>Expected number of iterations on current stage.</dd>
    </dl>
    <p>Callback should return value of: <strong>0</strong> for continue