Jim Stone breaks down the slide attack, where the middle attacker moves towards the right side and hits at the pin. The point of the slide is to beat the outside blocker to the ball and catch them off guard, but it's always important to gauge the opposing blockers and to have options for running slightly different slide options.
Stone gives his offense slide options by splitting the slide zone into four zones behind the setter: A, B, C and D.
A traditional slide is pushed to Zone D (all the way to the pin), but your setter can use the other zones if the blocker is already at the pin. Breaking the slide into zones allows more options for the hitter and setter to communicate about the blockers' location.