From Xojo Documentation
Called when a contextual menu item is selected. This selected item is contained in Item.
This example populates a contextual menu in the Open event of a WebToolbar:
Me.ContextualMenu = menu
The menu selection will be handled in the ContextualMenuAction event when the user right-clicks on the control. For example, it can be of the form:
There are equivalent events and properties for managing contextual menus on WebPage as well.