[e] (0) Try to clarify case matching rules for selectors
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=26560
Affected topics: CSS, HTML

git-svn-id: http://svn.whatwg.org/webapps@8764 340c8d12-0b0e-0410-8428-c7bf67bfef74