Detect mousedown button on polyline

[Pil]

Is there an official way to do that?

At the moment I'm using the property b (it's the second one) from the
MouseEvent object,
aka
google.maps.event.addListener(poly, "mousedown", function(evt) {

alert(evt.b.which);
});

But this isn't documented and therefore can change at any time without
notice.

[Enoch Lau (Google Employee)]

No, there's currently no supported way to get the mouse buttons. Please file a feature request: http://code.google.com/p/gmaps-api-issues/issues/list