FYI, castling rules are in the board's FAQ as well. I was looking for something that more specifically addressed your question, where say:

Black: Q-e4
White: K-e1, P-e2, R-a1

Now castling goes through the Q's attack on b1. I know this is a legal move to make. What I'm not certain of is whether the Q can then move to b1 and take the rook similar to en passent (spelling??)...

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