Font size according to field area

Hi All

Got a dynamic text box which get text from outer source, (fits to 20 chars).
I want the whole text to keep inside the box and shrink (font size) if text is too long.
Tried all of this options, none of them shirk the font size:(instance name=boxer)

//boxer.autoSize = TextFieldAutoSize.CENTER;
//boxer.wordWrap = true;
//boxer.width = 100;
//boxer.textWidth = 100;
//boxer.autoSize = "CENTER";
//boxer.scaleX = 1;
//boxer.multiline = false;
//boxer.textWidth = boxer.width;

Is there a simple code telling the text to stay in the text box and shirk its size ?