Dynamic creation of movieclip class, not object [AS2]

Is there another way to work with movieclip classes than attaching them from the library?

For instance say that I have a textbox class that extends the movieclip class. Puts it on the scene and then I’m free to work with it from the class as I want.

But inside this class I check if I need a scrollbar. If I do, then start a “sub-class” and create a scrollbar. I can have a movieclip in the library and attach it and have a new class on it. But what I want to do is write something like this

var clipScroll = createEmptyMovieClip(“scrollBar”, 3)
clipScroll = new com.texts.text_items.ScrollBar

the problem is if I do like this the class that I start is just an object. I can’t trace where it is, I cant create a movieclip inside it and trace where that is…

So long question short, Must I attach from library to play with “extendes MovieClip” in a class.