rel-contact
From Microformats
rel contact
rel="contact" was introduced by XFN 1.1 (http://gmpg.org/xfn/11) in 2004 and is in broad use across various social network sites (see services with XFN supporting friends lists).
Much later (~2007, citation needed), a draft of HTML5 redefined rel="contact" slightly differently (currently: HTML 5 (http://www.w3.org/html/wg/html5/#link-type3)).
Publishers should consider using the XFN 1.1 profile (http://gmpg.org/xfn/11) to explicitly specify the XFN meaning.
Parsers should assume the earlier, well established and in use XFN rel="contact" meaning unless they encounter a document explicitly labeled as HTML5 that also lacks a reference to the XFN 1.1 profile (http://gmpg.org/xfn/11).
This issue has been documented.
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