<https://www.9planetsdesign.com/blog/how-to-check-a-webpage-for-accessibility/site-navigation>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<http://schema.org/SiteNavigationElement>
<https://www.9planetsdesign.com/blog/how-to-check-a-webpage-for-accessibility/>