You’re currently looking at the rather outdated (while still most stable) version of the Multiselect Widget.
Please also have a look at the upcoming version http://github.com/michael/multiselect/tree/next, that is supposed to become v1.0 one day ;-).
Yanick’s demo shows the latest version in action:
http://yanickrochon.uuuq.com/multiselect/
If you have suggestions or did some nice modifications just let us know.
We’d be happy to review them, and perhaps include them.