From English Wikipedia, article 'Rules of chess':
If a player delivers a checkmate, the game is over and that player wins, no matter what is subsequently noticed about the time on the clock.
If player A calls attention to player B being out of time while player A is not out of time and some sequence of legal moves leads to B being checkmated then player A wins automatically.
If player A does not have the possibility of checkmating B then the game is a draw.
Can anyone provide a more detailed explanation what is 'possibility of checkmating' and who or what governs it? For example, I know that a king and a knight can checkmate a king with a rook. However, I don't think a king and a knight can checkmate a king with a queen. I didn't find a single checkmate position for that case (for weakest side, of course).
So, after exactly one of players had run out of time, who or what determines if his or her opponent has the possibility of giving a checkmate? I think it's quite essential because it means difference between a win and a draw.