[t] (2) Clarify hgroup's definition
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=20069
Affected topics: HTML

git-svn-id: http://svn.whatwg.org/webapps@7699 340c8d12-0b0e-0410-8428-c7bf67bfef74
[giow] (3) Match reality.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=18801
Affected topics: Rendering

git-svn-id: http://svn.whatwg.org/webapps@7700 340c8d12-0b0e-0410-8428-c7bf67bfef74