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func wall
From Quake Wiki
This is a solid brush with a few extra controls and characteristics;
It has a Targetname, which means you can perform the following actions during play;
Killtarget it If you put its targetname in the 'killtarget field of another entity, the func_wall will be removed when that entity fires. Typically a trigger_relay is used to do this, but be aware that it will not work properly under standard progs if the trigger_relay has both a target and a killtarget.
Swap its texture If the func_wall has a texture named +something then, when triggered by another entity it will change its texture to +asomething.
Because func_walls are brush entities, they do not create shadows and do not impact on vis compilation time.
Bug: Flickering entity This occurs when a large and/or complex brush entity crosses two or more vis leafs. It's a visual error whereby the entity will go invisible when the player is stood in a certain spot (ie. vis leaf).
The proper fix must come engine-side, the only mapside fix that can be done is to divide the func_wall into smaller ones that do not cross leafs.