Bugzilla – Bug 20474
html5.1 and the main extension spec are at odds
Last modified: 2013-01-16 09:23:00 UTC
HTML5.1 currently has a definition  of the main content that conflicts with the main extension spec 
request that the definition in HTML5.1 spec be removed and someone can then step forward to champion the definition currently residing in HTMl5.1 as an extension spec.
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Change Description: The main extension spec has been folded in.
Rationale: It's a good feature to support.