Quote Originally Posted by Curmudgeon View Post
A 541

Apart from blocking vision in one direction, the "window" of a Rope Trick is just an opening by which things can enter or leave the extradimensional space. You don't need special access procedures (no "opening" or "closing" the window) to get through in either direction, which means fireballs, missiles, and the like can also pass through (in either direction) without hindrance. To prevent spells from entering a space an opening must be less than 1 square foot, and the Rope Trick window is 15 square feet.
But still everything behind the window is not on the prime material plane (or wherever the rope rick was cast), so how can the fireball affect the contents of the extradimensional space?