User blog comment:Ohmyn0/Making your wiki HTML5 compliant/@comment-3147293-20120711023117/@comment-2200849-20120712113504

Yes, indeed $wgCleanupPresentationalAttributes will be enabled on Wikia by default, but it can make problems, i.e. it cannot always find a good substitute for the deprecated attribute. This is because it cannot take into account the element the attribute is on, so it might apply text-align: center; when margin: auto; would have been the correct course of action. You could report any problems—if you encounter them—to the MediaWiki bugzilla site.