For the meta element with the property attribute, I'm concerned that someone out there is going to use both attributes (name and property) for the same value strings but with different meanings. Unless creating the property attribute was simply a mistake, that's the likeliest use, and it's likely even if it was a mistake since it's now available to future developers. For now, we're stuck with hoping for the best with it, especially since Facebook and Google are supporting it and they're big players.

Would it help nip this in the bud if HTML5 were to state that the two attributes are interchangeable and therefore are not to both be used in the same element and that value strings for both shall have the same meanings? Or should the WHATWG MetaExtensions page (because it's linked to from HTML5) be explicitly expanded to require (or try to require) registration of property values? Or both? Or should property be deprecated now and reserved for possibly some undefined future use?