<https://forum.ppr.pl/index.php?/topic/26-ci%C4%85gniki-ursus/page/102/#comment-73794>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://forum.ppr.pl/index.php?/topic/26-ci%C4%85gniki-ursus/page/102/&tab=comments#comment-74061>