age-doc">EPUB 3.3 package document</a>. Although only few of those vocabulary items are <em>required</em> for a conformant EPUB specification, their formats, value constraints, etc., are normatively specified in the standard and these <em>must</em> be followed for a publication to be valid if they are used.
                    </p>
                </li>
            </ol>
            <section>
                <h3 id="exit-criteria-core">Exit criteria</h3>
                <p>The criteria are different for ea