The default value is Null. If this value is not changes, the C1RichTextBox control will show the simple Windows.UI.Popups.PopupMenu with the set of clipboard-related commands. You can set this property to the custom Windows.UI.Popups.PopupMenu object, or any object implementing C1.Xaml.IC1ContextMenu interface. In such case the C1RichTextBox control will show your custom context menu instead of default one.