<https://forum.unity-community.de/topic/16948-buttons-event-system-und-raycast-target/#comment-114796>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://forum.unity-community.de/topic/16948-buttons-event-system-und-raycast-target/?tab=comments#comment-114770>