Detecting a text change in a dynamic text field

I have a dynamic text box that gets its content from an XML file. When the use clicks on a nav item, a different node in the XML is displayed in the text box.

I’m looking for a way for the text box to be able to detect if the text it contains has changed.

I tried this, but it doesn’t seem to work:

function test(event:Event): void {
trace(“The text has changed”);
}

contentTxt.addEventListener(Event.CHANGE, test);

Is there a way to do this?