I figured it out by just doing it.
In flash tween engine the callback function is added at the end
and function itself is seperate.
but here you define the function name inside the function and the caller also,that's why I was a "little" confused.
I mainly asked for it for the other members and why the callback is important and an example to show them how it works.
This because it wasn't evident inside your provided examples.
Thanks for the example provided.
Others may benefit from it as well.