iframe cross browser communication

If you want the iframe of a site not of the same domain to transfer data to your parent site this is normally prohibited because of the potential security risk of cross domain access. So if you want to communicate you can send messages via javascript.
in iframe
$('.button').click(function(){window.top.postMessage('hello', '*');})
on parent site
window.onmessage = function(e){if (e.data == "hello") {alert('hello')}
this works the other way also.