A question came in the mail regarding the fact that the W3C validator currently fails on RDFa. This is true, and it will likely remain true until we finish the RDFa specification for XHTML1. RDFa does involve changing the XHTML schemas, and the plan is under way to do just that.
That said, it’s important to note that, for most RDFa use cases, only the about, property, and content attributes are new. It is currently under debate whether these extra attributes should indeed cause the validator to fail, and all browser implementations we have seen are perfectly happy to accept extra attributes, even in strict, XHTML mode, without any change in rendering.
In other words, prototype away. Validation will work soon. In the meantime, nothing else will break.
XHTML1 under User Agent Conformance, point 5, says “If a user agent encounters an attribute it does not recognize, it must ignore the entire attribute specification (i.e., the attribute and its value).”, so RDFa ought to work in any conforming browser. So, though it is not valid XHTML1, it is required to work in conforming browsers.
31 May 2006 at 10:00 am