The ZAD/concede question

[thejinhong]

In the Sharhrazad subgame, I Sword my opponent's Tog.  In response, he Brainstorms, finds no Force, and before Sword resolves, he concedes.  In response to the first Sword, I play a second Sword on the Tog.    

So the question: Does concession follow the stack?  And can you do it again and again as many times as you like?

[Kowal]

Concession doesn't use the stack.  When it's declared, the game is over.

[Jacob Orlove]

Concession doesn't use the stack.  When it's declared, the game is over.

And if you're in a subgame, that means you immediately return to the main game, and the loser is down 1/2 of his life.