Formating Dynamic text via Actionscript

I’ve got a dynamic text box that I am controlling from actionscript, but I can’t figure out how to make a certain sentence be centered. I tried using the center tags for html but it won’t work.

TextFieldInstanceName.htmlText = "<a href='asfunction:gotoAndPlay,frameNumberOrLabelHere'>THIS IS WHAT I WANT CENTERED, BUT <CENTER> DOESN'T WORK</a>";