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

html facebook xml-namespaces fbml
Rudiger picture Rudiger · Jan 10, 2011 · Viewed 55.9k times · Source

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

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

Answer

Matthew Scharley picture Matthew Scharley · Jan 10, 2011

While I haven't seen it in use, this is standard XML notation for extending the current XML namespace (in this case XHTML) with another one (in this case FBML). This tells your browser where to find the specification for FBML which in turn tells it how to handle the <fb:*> tags. Technically speaking, the value of the xmlns:* attribute is simply a unique identifier, but often it is a URL which points to a definition in one form or another. In this particular case the URL doesn't point to a definition unfortunately.

See W3Schools for more information about XML namespaces.

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