[icebraining]

- It needs a way to be semantic, so that common things on the internet must be representable, such as products, events, flight reservations, etc. XML solves this with namespaces. - It needs to be able to provide a way to show documents written in that language in current browsers using a plug-in. XML solves that with XSLT (there will be a standard .xls file for easy backwards compatibility). - It should be able to be just uploaded on an FTP server by the average author, just as HTML, without installing server-side software or messing around with settings. - It should be easy to write for authors.

Isn't that what RDFa is? Which has to advantages over HSS already: 1) it's designed to extend HTML while remaining compatible with older browsers and 2) It's already used by big sites and understood by Google.