Aaaahh, found it!!!
Facebook documentation: (http://wiki.developers.facebook.com/index.php/Fb:submit
Basically, anything contained within the <fbsubmit> .... </fb:submit> tags acts as a submit button. All of the tags that Facebook uses can be found at http://wiki.developers.facebook.com/index.php/FBML
. By the looks of things they have their own set of HTML markup tags. This is to ensure that everyone that develops applications to work with Facebook can integrate successfully.