Fair, but you sounded like you're really planning to crack down on it. Especially with your original statement that says "hidden" means that the target can't even be aware that a potential attacker exists. If that requirement is loosened, then there would be a lot more potential situations where hiding would be possible.The second section about the DM determining the circumstances that allow a character hide is Rules as Written though - you can find it in the errata for the PHB (or in the text of the second edition)
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