This entity works like a func_wall_fade with the difference that it encloses all the "func_" entities inside of it and treats them as a single func_wall_fade.
If you want to make an entity inside the zone to ignore the fading you need to check the flag "Not Fade (524288)" in that specific entity.
Starts Invisible (1)
If set, this func_fade_zone will start faded.
If you set a name for this entity, the func_fade_zone will need to be triggered to work, otherwise, it will automatically fade out if it obstructs the player.
On Receive Inputs
On -> Fade In (If a name is set).
Toggle -> Toggle Fade (If a name is set).
Off -> Fade Out (If a name is set).
Kill -> Destroy.