docs: def onRightDown(self, event=None):
          """ right button down: show pop-up"""
          if event is None:
              return
          # note that the matplotlib event location have to be converted
          if event.inaxes is not None and self.popup_menu is not None:
              pos = event.guiEvent.GetPosition()
              wx.CallAfter(self.PopupMenu, self.popup_menu, pos)
          self.cursor_mode_action('rightdown', event=event)
          self.ForwardEvent(event=event.guiEvent)