After a little research I found out the following about the func_door's properties:
target triggers its target every time the door stops moving, regardless it's opening or closing. Therefore it is triggered twice in a door's moving cycle, once on open and once on close.
fire on close triggers its target only after the door has finished closing.
Neither property disables the other one, so if both are set, when the door closes both will be triggered.
However, there doesn't appear to be a "fire on open" (the opposite of "fire on close", triggered only when the door opens).
The point of this research is to find out whether I can use these triggers to make a door play a custom sound instead of the default ones. As this research shows, it cannot be done without the aid of trigger_multiples.
Where was I going?
...
Oh right. Is there an easy way to do that besides this?
Also, is there a way to make a func_door close completely even if a player is blocking its path? Because as far as I know, even if damage is set to 10000, as soon as it kills the player it will return to its previous position.
Thanks!