Actually I have been meeting with the W3 Web Components spec author for about 2 months while we readied this. The document.register method that was recently added to the spec was in large part a byproduct of X-Tag and when browsers implement it (Firefox soon) X-Tag will use it internally in browsers that support it, as a polyfill always does. Once one browser implements the JS mentod, X-Tag will truly polyfill the method on document as well.