[etc]

Я за точность

import flash.geom.*;
import flash.display.BitmapData;
getTextBounds = function(txt) {
	var x = txt._x;
	var y = txt._y;
	var w = txt._width;
	var h = txt._height;
	var xs = txt._xscale;
	var ys = txt._yscale;
	var scale = 20;
	txt._xscale = xs*scale;
	txt._yscale = ys*scale;
	var bmp = new BitmapData(txt._width,txt._height,true,0);
	var mtx = new Matrix();
	mtx.scale(scale,scale);
	bmp.draw(txt, mtx);
	bmp.colorTransform(bmp.rectangle,new ColorTransform(1,1,1,1,0,0,0,255));
	var rect = bmp.getColorBoundsRect(0xFF000000,0x00000000, false);
	bmp.fillRect(rect,0x80FFFF00);
	rect.x /= scale;
	rect.y /= scale;
	rect.width /= scale;
	rect.height /= scale;
	txt._xscale = xs;
	txt._yscale = ys;
	bmp.dispose();
	return rect;
}
rect = getTextBounds(txt);
beginFill(0xFF0000, 30);
trace(rect);
moveTo(txt._x+rect.x+2,txt._y+rect.y+2);
lineTo(txt._x+rect.x+rect.width+2,txt._y+rect.y+2);
lineTo(txt._x+rect.x+rect.width+2,txt._y+rect.y+rect.height+2);
lineTo(txt._x+rect.x+2,txt._y+rect.y+rect.height+2);
endFill();