FocusManager - Adobe ActionScript® 3 (AS3 Flash) API Reference

In case you were befuddled... if you want to do a tab loop in a certain clip, for instance, myPopUp, then you just use

fm = new FocusManager(myPopUp);

Use the tabIndex property to dictate the order if it is not in the order that you want.

myText.tabIndex = 1;

myText2.tabIndex = 2;

myButton.tabIndex = 3;

myCancel.tabIndex = 4;