This package adds native a "fullscreen" button to Tk windows on Mac OS X 10.7 and later. The package adds the fullscreen button that, when pressed, will smoothly animate the window to fullscreen status. The window can be restored to its previous state by clicking the upper right-hand part of the screen and locating the button in the menubar. This package has no relationship to the standard Tk command "wm attributes $w -fullscreen 1," which also implements a fullscreen window and tracks its state internally through Tk. Under OS X, the "wm attributes" command uses different API's and its state can be tracked and configured via Tk. The "::fullscreen::fullscreen" only adds the fullscreen button to the window, and does not track the window's state; setting the window to fullscreen state is triggered by the user. The benefit of this command is that it provides better integration with modern Mac API's.