How to find HWND of vruby VRForm

This is most likely down to my lack of experience with Ruby but I am
struggling to obtain the microsoft windows HWND relating to a VRForm
object when using VRuby.

The class hierarchy indicates
that VRForm inherits from SWin::Window which has the property hWnd.

However, attempting to refer to this property using the following;

puts MyForm.hWnd

gives the error;

undefined method `hWnd’ for MyForm:Class (NoMethodError)

If I create an SWin::Window I can successfully refer to the hWnd

Since VRForm derives SWin::Window why can’t I refer to that property?