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A bid, not intended as a place to play, which denotes a control (usually first or second round). The control need not be in the denomination named, These bids are used to investigate slam
but then never actually refers to them anywhere else.
Maybe it's because they were only thinking of the slam investigations, which are usually above 3NT -- there's a general rule that bids above 3NT do not get immediate alerts starting with opener's rebid, so there's no need to say whether these are alertable. But that still suggests that they should get a delayed alert, which no one ever does, either.