Set transformation point in AS?

How would I make this grow from right to left?

import mx.transitions.Tween;
import mx.transitions.easing.*;
var toplinein:Tween = new Tween(topwhiteline, "_width", Strong.easeOut, 0, 929, 8, true);

I tried just moving the transformation point to the right side, but AS doesn’t seem to care

Thank you