he index is to be placed directly inside a <span class="emphasis"><em>book</em></span>
          or <span class="emphasis"><em>part</em></span>, in which case you should probably use the
          same XML container for the index as you use for whatever subdivisions are
          in the <span class="emphasis"><em>book</em></span> or <span class="emphasis"><em>part</em></span>. In any event
          placing a <span class="emphasis"><em>section</em></span> within a <span class="emphasis"><em>book</em></span>