I'm not claiming a double toe tap does it. Look at the Jags TD we just watched. The receiver caught the ball, did a toe tap, lifted it off the turf and then went to the ground with the same foot where his foot touched and then rolled over to get the ankle/shin down. If a double tap was all that was needed, there wouldn't have been any discussion by the TV crew about having a shin down. As soon as the foot touched down the second time before rolling over, it's a catch no matter what. But because "both feet" are required and he didn't get his second foot down, you turn to the "OR" part of the rule that states any body part = both feet except a hand. So then you look for the ankle/shin down in bounds. Even without the first toe tap you look for the ankle/shin in the absence of "both feet." It's clear to me it has to be left and right foot but there's the "or" to use other body parts as a sub.
