optional, single

—

Inside <validdate> the date is given until a specialty is valid (if existent).

<certification>

<date>

<certification>

(see also <certification>)

<validdate>
    <date>
        <year>2007</year><month>2</month><day>28</day><dayofweek>3</dayofweek> <!-- Wednesday -->
    </date>
</validdate>