on OSX, how can i set the "changed" flag, which shows as a red dot in the window icons?

On OSX every standard window frame has 3 circular icons in the upper left corner of the window, corresponding to red (close window), yellow (minimize), and green (maximize).

when the user changes the contents of their document, you are supposed to change the icon from a clear red icon to one with a black dot in the middle, indicating it has changed.

I can't find anywhere in NativeWindow to do this. Surely i can't be the first person to want to set the "changed" flag in the window frame.

help is appreciated.

edward