It is not for tagging a URL.The new
rel="tag"syntax we have proposed and adopted is attempting to solve a particular problem — how to tag web pages or blog posts.
It seem that there is demand for a general decentralised syntax for tagging URLs, and that is certainly something to think about, but this is not meant for that.
Tags do not require Technorati-proprietary URLs.The tag help pages on the Technorati site can be read in that way, but they are focused around linking to the pages themselves; the underlying specification is clear that the url is to a 'tagspace' - a place that collates or defines tags.
I think this is an elegant way for the 'namespace' discussion to be resolved - if there are colliding meanings for a tag, you can link to a disambiguating tagspace, just as Tim describes.
Tags are not invisible metadata.They are meant to be visible links on your page and in your posts. The 'this is just like meta keywords and will suffer the same death' argument misses this point.
Part of the Google insight was that visible data is more trustworthy than invisible metadata - the links that people make visible on their pages are more part of their work than those they hide away for robots alone. Of course it doesn't make them immune to gaming, but it does make the gaming rather more obvious to human readers, especially to authors, who may not always be aware what invisible metadata is being generated on their behalf.
<link rel="tag" href="..." />syntax is not read by the Technorati spider.
This point is also behind some of the problems people have had with having their links picked up by the Technorati spiders - they sequester the tags away between posts, and omit them from their feeds. We're working hard on improving our tag detection (and many thanks to people who have spent time going back and forth on this with us, especially Stephanie), but we do expect them to be part of the post body.
I hope this makes more sense now; we'll continue updating the formal spec and discussion pages in the light of this feedback.