This property is not relevant for this class.

You can use this property to switch between complete menu sets at run time. For example, you can define one System.Windows.Forms.MainMenu to be displayed when your multiple document interface (MDI) form has no active MDI child forms and another System.Windows.Forms.MainMenu to display when a child window is displayed. You can also use a different System.Windows.Forms.MainMenu when specific conditions that require displaying a different menu set exist in your application.