Returns whether the exit in the given direction from the given room is open. This means that it must first be a passable sort of exit, and second it must not currently be impeded by, for example, a closed door. The second argument is the direction, as one of the strings 'north', 'south', 'east', 'west', 'up', or 'down'.
While this function is not settable, the open status of a door can be set with the flag function.