From Xojo Documentation
PresentContextualMenu displays the contextual menu assigned to the WebControl.
By using this method, the user does not need to right+click to trigger the contextual menu. For example, if PresentContextualMenu is called in the MouseEnter event, the contextual menu will display whenever the mouse enters the control.
Regardless of whether the menu is displayed by right-clicking or by calling PresentContextualMenu, the ContextualMenuAction event handler is called when a menu is selected.
Display the contextual menu attached to a Button: