<https://webaccessibile.org/articoli/analisi-atag-20-w3c-working-draft-22-november-2004/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://webaccessibile.org/articoli/analisi-atag-20-w3c-working-draft-22-november-2004/>