The template for sect3.titlepage generates:
<h3 class="sect3">
<a id="{id of sect3}" name="{id of sect3}"></a>
<h4 class="title">
<a id="{id of sect3}" name="{id of sect3}">i{title of sect3}</a>
</h4>
</h3>
resulting in double definition of the same id, which is a validity error
in XML documents.
Replace with the same template as for sect2, using h3 instead of h2.
