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You call this being "fully behind HTML5"? http://grab.by/grabs/0b694089e83975c385627b134ee8ece7.png Even Microsoft's better than this. edit: could whoever downvoted me explain why he did so?
That's not inconsistent with being "fully behind HTML5". That page is meant to show off how Safari handles various HTML5 features. If you view it in a different browser, it is not showing you how Safari handles those features. Hence, it makes perfect sense for it to try to limit itself to people using Safari.
Isn't the point of HTML that all browsers handle it similarly? If that link is restricted to one browser, it isn't better than all the "Designed for IE6" sites you used to see in the early '00s, and absolutely no evidence of Apple being "fully behind HTML5".