2017-05-19 UTC
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Zegnat “Conformance checkers must use the information given on the microformats wiki existing-rel-values page to establish if a value is allowed or not: […] values marked as "discontinued" or not listed in either this specification or on the aforementioned page must be rejected as invalid.” - https://html.spec.whatwg.org/multipage/semantics.html#other-lin