what does "they knew their viva subscribers."mean?
"President John F. Kennedy, visiting the Alamo City for the first time, flew into San Antonio Thursday to a wildly enthusiastic greeting." The editors of the Light hadn't been guessing. They had known the greeting would be enthusiastic, because they knew their viva subscribers. A school holiday had been proclaimed, stores had put up their Christmas decorations a week early, labor was out in force, the Democratic organization was marshaling the party faithful.