Couldn't find a solution - dynamic text in a button

I’ve scoured a lot of sites but found nothing that could help…

Simple problem…Created a text box and assigned an instance name of mainText…

Created a button with an instance name of mainBtn and placed an instance of the mainText textfield inside…

AS2 solution --> mainBtn.mainText.text = “Some New Text”; and it WORKS!!!

AS3 solution --> dunno yet…one thing’s for sure, the code above doesn’t work…tried a bunch of things, none work…

Tried adding root, this, stage, and none of them help…Always comes up with “Access of undefined property instanceName through a reference with static type flash.display:SimpleButton”

I need to write several of these so, naming the textfield inside a button should be the most efficient way…right???

Other solutions provided involved some XML file solution…Don’t even need that…Just need something simple that works…

Also, I’m trying to write all of my code in an AS file…Any help would be very much appreciated…Also, if possible, please post some code…Ready to tear my hair out!!!