trigger_hierarchy

trigger_hierarchy is a brush entity available in Portal 2.

Entity description

A trigger volume that can will check if any of trigger's children pass a secondary filter.

Child Filter Name <filter>: Filter to use to see if activator's children trigger me. See filter_activator_name for more explanation.
Delay Before Reset <integer>: Amount of time, in seconds, after the trigger_multiple has triggered before it can be triggered again. If set to -1, it will never trigger again (in which case you should just use a trigger_once).

TouchTest: Tests if the trigger is being touched and fires an output based on whether the value is true or false.

OnTrigger: Fired whenever the trigger is activated.
OnTouching: Fired when the TestTouch input is true (something is touching the trigger.)
OnNotTouching: Fired when the TestTouch input is not true (nothing is touching the trigger.)

Trigger:

OnEndTouch: Fired when an entity stops touching this trigger. Only entities that passed this trigger's filters will cause this output to fire. (activator is the exiting entity)
OnEndTouchAll: Fires when the last entity in the entity's area exits this trigger or when this entity is disabled. Only entities that passed this trigger's filters are considered. (activator is the last exiting entity)
OnTouching (New with Half-Life 2: Episode Two / Source 2007)
OnNotTouching (New with Half-Life 2: Episode Two / Source 2007): Fired when the TouchTest input is called.

TriggerOnce:

OnStartTouch: Fired when an entity starts touching this trigger. The touching entity must pass this trigger's filters to cause this output to fire. (activator is the toucher)
OnTrigger: Fired whenever the trigger is activated. (activator is the activator)

Targetname:

OnUser1 to OnUser4: These Outputs each fire in response to the firing of the like-numbered FireUser1 to FireUser4 Input; see User Inputs and Outputs.
OnKilled (Only in the Left 4 Dead series): This Output fires when the entity is killed and removed from the game.