The answer at 1a dictates the rules of the game.
Rule 1 affects FIVE clues in both wordplay and grid entry.
Rule 2 affects FIVE other clues in both wordplay and grid entry.
Rule 3 disallows something which appears in the grid as an unbroken sequence of letters. These letters are omitted from wordplay in FIVE clues whose answers pass through them.
One grid solution breaks Rule 1, another breaks Rule 2.
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