See https://rawgit.com/w3c/aria/master/aria/aria.html#heading (bottom of the "Characteristics" table)
<rdar://problem/29247607>
Created attachment 294708 [details] Patch
Comment on attachment 294708 [details] Patch Clearing flags on attachment: 294708 Committed r208696: <http://trac.webkit.org/changeset/208696>
All reviewed patches have been landed. Closing bug.