tween is an actionscript class and can be used after importing the core files.

import mx.transitions.Tween;
import mx.transitions.easing.*;
//Tween( obj:Object, prop:String, func:Function, begin:Number, finish:Number, duration:Number, useSeconds:Boolean);

e.g.

var myRot:Tween = new Tween(myText,     "_rotation", Elastic.easeOut,   0, 360,         3, true);