On this site the explanation of the batter hitting the ball while out of the batter’s box (rule 6.02) says if any part of the foot is outside the batters box the batter is out. But the rule says the entire foot has to be outside the batters box.
Where on the site did you see this information? The rulings here are very good, and 6.03 (not 6.02) rules that the foot must be entirely outside the batter’s box.