// Otherwise, Go does not return to its caller until main does, at which point it returns nil.
// After it returns, you cannot call future ui functions/methods meaningfully.
// (TODO ideally we would want to be able to call ui.MsgBoxError() to report failures to the user, but I would need to figure out how to do this on platforms other than Windows.)
// AppQuit is pulsed when the user decides to quit the program if their operating system provides a facility for quitting an entire application, rather than merely close all windows (for instance, Mac OS X via the Dock icon).
// You should assign one of your Windows's Closing to this variable so the user choosing to quit the application is treated the same as closing that window.