A) Planner declares only @V destination, template mentions {{flights}} {{hotels}} {{activities}}.
   omit nothing: Value for the variable 'hotels' is missing
   omit flights: Value for the variable 'hotels' is missing
   omit hotels: Value for the variable 'hotels' is missing
   omit activities: Value for the variable 'hotels' is missing

B) Planner declares @V destination, @V flights, @V hotels, @V activities.
   omit nothing: OK: Fly AI-101, stay at Hotel Alfama, ride Tram 28.
   omit flights: Missing argument: flights
   omit hotels: Missing argument: hotels
   omit activities: Missing argument: activities