There are events that are scripted in the game, like Half-Life, only on steriods
. There's a lot of events that are there to provide atmosphere, some are for setting, some are gameplay (as in you interact with them for certain outcomes). It all depends upon that part of the game.
As for the Snipertown level for example. There are a few guys in there that are designed to die in certain sequences, but there are plenty others in your squad where if you don't get the sniper in time, they'll pick them off. Thus the size of your squad will diminish, making certain confrontations later in the level harder. There really isn't a single definition to cover all the events that happen across the game because they are all done to further the gameplay, or interaction, or atmoshpere at the desired times
.
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Latuh fuh U,
Benson
benson@2015.com
"We don't introduce or cause bugs in the game, we merely find and bring to light the inadequacies within the code."
-regarding level designers