In my area it is relatively common to play 2D response to 1NT as three way.
EITHER Xfer to H,
OR balanced raise to 2NT without 4cd Major,
OR balanced slam try.
So a response of 2D is alerted (not announced) and opener usually rebids 2H.
Now suppose opener's LHO doubles 2H (having been silent before)
Again commonly this is played as T/O, because 2D is most frequently a transfer. If so is it alertable?
BB 4B2(d) suggests this is a Dbl of a suit bid that doesn't show the suit bid, thus T/O Dbl alertable.
But BB 4H5(b)says completions of Xfers are deemed to show the suit, thus T/O Dbl not alertable.
There is a twist to this, but I'd like a consensus on this issue first!