What is OpenID "Automatic Login"?

I've never heard this term in a technical sense until today. It has suddenly appeared in Facebook's marketing blog in reference to their new deal with Google.

To be clear, they assert that virtually no other OpenID providers besides Google implement OpenID "Automatic Login", thus no other OpenIDs are currently supported by Facebook.

Does this even exist?

FYI, yes this is a programming question. I would really love to see the ***API documentation*** for this feature. Please post a link to it if you are familiar with it. Thanks!!

Facebook announcement:
<http://www.insidefacebook.com/2009/05/18/facebook-launches-openid-support-users-can-now-login-with-a-gmail-account/>