warning when closing app on non-saved information on Envision page.

Make it so if you try to close a page while your editing Envision page that it will warn you that you haven't saved the information yet (or just auto saves it?) I was writing out my mission statement in it and I lost everything because I accidentally closed it before hitting save. Yes I should of just pushed save but most apps would warn you when you try to close their page with unsaved information.