From Yoast and very cool:
Google, Yahoo and Microsoft have just announced a new tag, which we can use to tell the search engines which URL it should have for the current page. This is probably best explained with an example, so here goes.
Suppose you have read my Twitter Analytics post, and you’ve started tagging all the URLs you spread on Twitter with Google Analytics campaign variables. So at some point, Google enters your site through this URL:
If it did, in "old times," this would mean you'd have a duplicate content issue: the same content indexed under two different URLs. An issue SEOs have been trying to solve on web pages for ages, which sometimes created huge limitations. This is where the new tag comes in. You add this code to the
<head>section of your page:
<link rel="canonical" href="http://yoast.com/twitter/analytics/" />
Read the rest of Yoast’s post and learn more about canonical URLs at http://yoast.com/canonical-url-links/. Google’s official post on canonical URLs is at http://googlewebmastercentral.blogspot.com/2009/02/specify-your-canonical.html.
While I appreciate Yoast blogging about this and their work in preparing the plugin, extension and module, one small critique. Technically, this is not a new “tag,” rather it is simply a new value for the
rel attribute of the existing