The extensibility story should maybe use the wiki registration style like<link rel> keywords.Sorry, I'm not quite following what you mean by this.
http://www.whatwg.org/specs/web-apps/current-work/multipage/links.html#concept-rel-extensions http://www.whatwg.org/specs/web-apps/current-work/multipage/semantics.html#concept-meta-extensions -- Simon Pieters Opera Software
