actionscript 3 - AS3 - using dynamic Text as a mask -

pretty sure possible. need dynamically load , populate textfield, , in turn use text mask on movieclip below it. have

function domask():void{     mymc.dynamictxtfield.text = "some text use mask";     mctobemasked.mask = mymc; }  domask(); 

what happens entire textfield being used mask, not text contains.

i'm not sure how use dynamic text mask, can achieve similar effect blend modes. e.g. multiply image on top of dynamic text on black background.