What is the "accessTokExtra" parameter in everyauth's facebook connect user creation callback function?

The code for everyauth's facebook findOrCreateUser() function is as follows:

everyauth.facebook.findOrCreateUser(function(session, accessToken, accessTokExtra, fbUserData){ });

Can anybody share what the accessTokExtra parameter is exactly?

Best,
Sami

It contains access token's expiration date.