Run-Time Problem
Attempt to move the player off-stage (P61)
    

Most problems are detected when Inform translates the source text, but this is one of the exceptions, a "run-time problem" which emerges only during play.


The player always has to be inside some room, though sometimes indirectly so - for example, it's okay for the player to be on a table inside a room, or in a box on that table. But it's not okay (for example) to write now the player is on the oak table and then now the oak table is nowhere.