handler(). This pointer should be used to pass
        additional data to callback (i.e. thread local data and so on).</li>
      <li><strong>file</strong> is the name of the RAW file whose processing
        evoked the file read error. This name <strong>can be NULL</strong> if
        underlying data input layer does not know the name. So, if calling
        application sets own callback, this callback should work with NULL file
        name.</li>
      <li><strong>offset</strong> is -1 at end-of-file (if 