Textfield not visible in parent Sprite

programming flash
1

Given this:

var container:Sprite = new Sprite();

var _myriad = new _Myriad();
var tff:TextFormat = new TextFormat(_myriad.fontName, 24);

var tf:TextField = new TextField();
tf.embedFonts = true;
tf.autoSize = TextFieldAutoSize.LEFT;
tf.text = "Hello world";
tf.setTextFormat(tff);

…why is it that I can see my text when I do this:

addChild(tf);

but I can’t see my text when I do this:

container.addChild(tf);