mouse_valid
		Indicates whether the mouse pointer is within the engine window. This flag can be used to suspend mouse reactions when the mouse is outside the window.
Range:
		1 - mouse pointer within the engine window.
        
 0 - mouse pointer outside the engine window.
        Type:
		var, r/o
		Example:
        if (mouse_valid) {
  force.x = key_force.x + mouse_force.x; 
} else { 
  force.x = key_force.x; 
}
        See also:
        mouse_sync