ZDoom

Essentially, jumps to the offset/state if the actor is moving onto a floor lower than it's maxdropoffheight (direction 0) or higher than it's maxstepheight (direction 1.)

For monsters that jump up to floors a bit too high for them to step onto or too low for them to fall on them.

Can't be done in DECORATE. Furthermore, such moves are disallowed by the physics code so the situation will never happen to monsters that check these variables unless some sector's height changes below them.