Linedefs can be activated regardless of player's Z position

In any game that uses the Doom engine, linedefs can be activated regardless of the player's Z position. This has the side effect of allowing the player to flip a switch despite being at too high or low of a height to reach it, or even if it is hidden in the floor. In some maps, this can provide a shortcut of a varying degree depending on what the switch does.

A well-known instance of this in an IWAD occurs in Doom II MAP01: Entryway, where it is possible to activate the switch in the northernmost room leading to the secret in that area, even if the mainframes have already been lowered. A much more extreme example of this, however, is in HacX MAP16: Protean Cybex. The intended goal of the level is to find and trigger four switches throughout the level, in order to reveal the exit switch, which is hidden in the floor in the center of the map, right behind where the player starts. Because of this bug, however, the player can simply turn around, and hit the switch, ending the level as soon as it begins.