This was suggested by karsten in legacy/trac#21166. An answer on StackOverflow details a bookmarklet for validating the generated HTML as is currently loaded on the page. I think it's worth digging into this as we've seen in legacy/trac#21166 and legacy/trac#21234 that mistakes can slip through. The bookmarklet is here: http://stackoverflow.com/questions/10377840/making-finding-html5-validator-bookmarklet/10420384#10420384 Once digging is completed, any issues found should be filed as tickets (preferably with patches for review).