createTextField() doesn't work anywhere but on _root

Hi,
I feel like I’m missing something obvious here, but I’m unable to add a textfield to any movieclip that I’ve attached to _root. Here’s a generic example:

_root.attachMovie(“generic_mc”, “clip1”, this.getNextHighestDepth());
rect1._x = 200;
rect1._y = 200;

_root.clip1.createTextField(“my_text_box”,10, 0, 0, 100, 30);
my_text_box.text = “this is a test”;

The text simply will not show up, no matter what I try. Now, if I simply create the text field on _root, of course everything works without a hitch. Am I just trying to do the impossible; is it only possible to dynamically put a text field in _root?

Thanks in advance,
John