  <li><b>Page spacing</b> Determines both vertical and horizontal space displayed
between pages.</li>
    <li><b>Thumbnail spacing</b> Determines both vertical and horizontal space
displayed between thumbnails.</li>
    <li><b>Thumbnail size</b> Determines the size of the thumbnails.</li>
    <li><b>Cache size</b> The program will try to cache rendered pages within this
limit increasing rendering speed at the cost of increased memory usage.</li>
    <li><b>Prefetch</b> The program will try to render pages t