Class extending MovieClip question, Some Help Please

Hi,

I’m wondering if there is a way of extending a class which is extending the movieClip class?
Or generally a way to add extra methods to an allready existing class without having to add them in the actuall class declaration.
I was thinking of using Interfaces but how can I implement an Interface to a class which is extending a movieclip?
as far as I know I have to write something like this:


import interfaceName
class className implements interfaceName{
//stuff
} 


but where do I put the code which extends the MovieClip?


class className extends MovieClip{
//
}


Cheers,
Manorius