Overprint question

If I were to select some text, then checkmark 'Overprint Fill' in the 'Attributes' pane, is there a way to tell with JavaScript that the text was set to overprint?

I've been experimenting with this code in ExtendScript, but it keeps returning false:

var doc = app.activeDocument;

$.write(doc.textFrames[0].textPath.fillOverprint + '\n');

Thanks.

Jay