All InteractiveObject based object can be focused :

You don’t need the fl.managers.FocusManager to set or remove the focus on objects :

// to set the focus
stage.focus = myTextField;

// to remove the focus
stage.focus = null;

If the focused InteractiveObject is hided, it loose the focus :

stage.focus = myTextField;

trace(stage.focus); // output : [object TextField]

myTextField.visible = false;

trace(stage.focus); // output : null

To remove the crappy yellow rect on all focused InteractiveObject :

stage.stageFocusRect = null;