Looking for info on callbacks

Hello,

I am using RT3, and read a post from last year regarding callbacks.

I have hacked the ShowPeople element to display data such as last login
from our website, but it seems to me that the maintainable way to do
this would be with a callback.

Is there any more info than this post
(http://lists.fsck.com/pipermail/rt-devel/2002-December/002833.html)
regarding callbacks?

Thanks,
David Swift