Is a first baseman standing on the foul line in fair territory?

There is no such rule Official Baseball rule book section 4.03: When the ball is put in play at the start of, or during a game, all fielders other than the catcher shall be on fair territory. However the N.A.P.B.L. Umpires Manual also states: Do not insist on the first baseman playing with both feet in fair territory unless the offensive team protest. Then enforce it equally for both teams.