I found many ways to declare opengraph. But which one is the "right" way?
http://ogp.me/ use in source code
<head prefix="og: http://ogp.me/ns#">
but in examples the html-tag instead:
<html prefix="og: http://ogp.me/ns#">
combination with facebook look like
<html prefix="og: http://ogp.me/ns# fb: http://ogp.me/ns/fb#">
or without prefix
<html xmlns:og="http://ogp.me/ns#" xmlns:fb="http://ogp.me/ns/fb#">
ogp.me link to imdb as example that use it this way
<html xmlns:og="http://ogp.me/ns#" xmlns:fb="http://www.facebook.com/2008/fbml">
another sites set the og:type "website" or "article" inline like
<html prefix="og: http://ogp.me/ns# fb: http://ogp.me/ns/fb# website: http://ogp.me/ns/website#">
ogp.me link zu a doc: https://de.scribd.com/doc/30715288/The-Open-Graph-Protocol-Design-Decisions See page 15; It said don't use this form?
xmlns:og="http://ogp.me/ns#" xmlns:fb="http://ogp.me/ns/fb#"
So much combinations, another websites do nothing of it and only use simple the meta-tags. Is the declaration optional or which one should I use in which form?