.w3.org/TR/epub-33/#sec-xhtml-deviations">restrictions on XHTML</a>, the <a href="https://www.w3.org/TR/epub-33/#sec-nav">format of an XHTML navigation document</a>, or the <a href="https://www.w3.org/TR/epub-33/#sec-xml-constraints">requirements on XML conformance</a>.
                    </p>
                </li>
                <li>
                    <p>
                      Vocabulary items which serve as metadata for the publication, and added to the <a href="https://www.w3.org/TR/epub-33/#sec-pack