I was just playing around with a potential itinenaries for our trip and tried e.g. something like JNB-MRU-LHR-ARN-LHR-DFW-HNL-NRT-HKG-AKL-SYD-LHR-CDG-LHR-NBO -- two "stops" in Europe. While the route is presumably fine (four flights in EUR), the ..LHR-CDG-LHR-.. is just transits.
Perhaps MM could indicate the parts of a route when only transit is possible?