Crampedin13A: "YTO would have made more sense than YYZ"

YTO is a code for a city while YYZ is a code for a specific airport. Many large cities worldwide have a city code (i.e. LON) and then many ariport codes all associated with the same city (i.e. LHR, LGW, etc.)

If YTO is used in the fare basis, it means that the basic fare (excluding taxes, fees, etc.) would, according to IATA rules, in theory, be exactly the same for flights in to/out of any Toronto (YTO) airport.