[Jim S]

Ah, you've fallen into the trap!
The passer may throw a legal pass from in or behind the neutral zone......but not the expanded neutral zone.
The expanded neutral zone is for blocking purposes.
It allows an offensive lineman to make immediate contact with a B player and drive them backwards as long as they stay in the expanded neutral zone.
Even if contact is maintained, if the player proceeds beyond the expanded zone, he is now downfield illegally.
The passer is restricted to the neutral zone as defined by the ball at the start of the play. In other words his feet can't go beyond the down box before the pass. (well if they do he CAN go back.....)