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It seems this is in Chrome and Internet Explorer and Gecko is considering: https://bugzilla.mozilla.org/show_bug.cgi?id=471020 We should figure out how it works and define it (I suspect there will still be some amount of "sniffing"; e.g. all image types going into the same image library).
Yup. :) *** This bug has been marked as a duplicate of bug 19865 ***