As Facebook no longer allows us to register new FBML canvas application, new canvas applications have to be iframe canvas apps. One of the most frequently asked questions in developing iframe canvas apps is how to use the multi-friend-selector in our canvas (e.g. as an input field inside a html form).
The best solution would be have a “native” input element for the multi-friend-selector for iframe canvas apps. However, Facebook has not provided such a solution for us and we have to build our own multi-friend-selector.
If building such a multi-friend-selector is too troublesome for you, why not simply use one that is available in the market? Visit http://forum.developers.facebook.net/viewtopic.php?id=100284 for the details.