A single-line whip is a guide to what the party's policy would indicate, and notification of when the vote is expected to take place; this is non-binding for attendance or voting. A two-line whip , sometimes known as a double-line whip , is an instruction to attend and vote; partially binding for voting, attendance required unless prior permission given by the whip. A three-line whip is a strict instruction to attend and vote, breach of which would normally have serious consequences.
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