Код:
var txt:TextField = this.createTextField ("txt", 0, 100, 100, 400, 50);
txt.html = true;
txt.autoSize = true;
txt.htmlText = "<font size='64'>W</font><font size='32'>W</font><font size='16'>W</font>";
var fmt1:TextFormat = txt.getTextFormat (0, 1);
trace (fmt1.size);
var fmt2:TextFormat = txt.getTextFormat (1, 2);
trace (fmt2.size);
var fmt3:TextFormat = txt.getTextFormat (2, 3);
trace (fmt3.size);