import flash.events.FocusEvent;

stage.addEventListener(FocusEvent.FOCUS_IN, onStage_FOCUS_IN);

function onStage_FOCUS_IN(event:FocusEvent):void
{
	focusInPath(DisplayObject(event.target));
}

function focusInPath(dispObj : DisplayObject, s : String = ""):void
{
	if (dispObj.parent != null) {
		focusInPath(dispObj.parent, s + "." + dispObj.name);
	} else {
		var a:Array = s.split(".").reverse();
		var output:String = "";
		for (var i : Number = 0; i < a.length; i++) {
			output = output + "." + a[i];
		}
		trace("FOCUS_IN: " + output.substr(1, output.length - 2));
	}
}

This code traces out the name (and display list path) of the object that currently has focus. This handy when you are testing the tab order and you can't see a yellow rectangle anywhere.

AS3 Keep Track of Where FocusRect Is Whilst Tabbing

path

ActionScript 3