[e] (0) Clarify a bit
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=22001
Affected topics: Video and Audio

git-svn-id: http://svn.whatwg.org/webapps@7943 340c8d12-0b0e-0410-8428-c7bf67bfef74

Author:    ianh <ianh@340c8d12-0b0e-0410-8428-c7bf67bfef74>