In L4D (others maybe too) there is an entity named env_player_blocker. This entity is a point entity, and thus invisible. it also has these two properties that set the bounds of the entity (which blocks players from entering those bounds)
Code:
"origin" "6664 3918 608"
"mins" "-4 -90 -70"
"maxs" "4 80 80"
"initialstate" "1"
"BlockType" "0"
"classname" "env_player_blocker"
The mins and maxs set the bounds, creating a box of some sort. This is hard to create in the game as you can image, since you cannot visually see the bounds of the entity.
Can someone create a visualizer that would paint the bounds of this entity?
Some other handy things would be
1) Set entity position to where I'm pointing
2) Adjust entity XYZ position by VALUE
3) Set mins\max
4) set BlockType to 0,1,2
5) dump data out to text file of the current pointed-at entity