A Boolean value that indicates whether the window is the key window for the application.
The value of this property is
true if the window is the key window for the application; otherwise,
Managing Key Status
Moves the window to the front of the screen list, within its level, and makes it the key window; that is, it shows the window.
Invoked automatically to inform the window that it has become the key window; never invoke this method directly.
Invoked automatically when the window resigns key window status; never invoke this method directly.