HTML: What is `xmlns:fb=“http://www.facebook.com/2008/fbml”`?

Question

What is xmlns:fb=\"http://www.facebook.com/2008/fbml\"?

I\'ve been seeing it in a lot of tags recently. What does it do?

Answer 1

Just as @Matthew Scharley said, its used to embed Facebook-specific tags on your site. For example, here's our company's Facebook stream on our site. Another common use it the "Like" button on website. More information can be found on the Facebook developer site.

UPDATE

Here's some additional widgets/plugins.