What kind of code is http://ogp.me/ns/fb#
I'm not asking what it does, in the sense of, "It makes your Facebook Like button work."
What I am asking is, is this javascript, is it css, or what? It looks like a class. If I wanted to write my own similar file, what extension would I use to name it?
The reason I am asking is I would like to make my own class, for my own widgets, and reference my own class by putting something like xmlns:zz="http://mydomain.com/mylibrary/zz#"
Answer
It is JSON, as the name implies is a subset of JavaScript, but as it is designed for encoding data not code it can actually be parsed by most programming languages.
The extension don't matter but could be .js as it is commonly served with the MIME type text/javascript.
The is no way of using it with XML namespaces as you are hoping.