<https://journals.biologists.com/dev/issue/138/18>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://cob.silverchair.com/dev/article/138/18/3977/44619/Fgf-and-Hh-signalling-act-on-a-symmetrical-pre?searchresult=1>