[1] Texas is used in response to a notrump opening when holding a six-card or longer major suit and at least game-going features; responder may have interest in slam via continuations in Blackwood or its variants.
The standard defense to the Texas transfer: double is one-suited and lead-directing, 4NT is for the minors, four of responder’s suit is a Michaels cuebid.
[2] NW ES The 4♦ response is the Texas transfer conventional bid, is alertable and requires opener to rebid 4♥.
[4] This effective pre-emptive sequence by East-West gives North-South no convenient way to discover their eight-card spade fit and a plausible 4♠ contract.
With minor suit bids being more distinctive, opener is more likely to recognize them as the partnership agreement requesting a transfer to a major.