A 2♥ or 2♠ opening is a weak two: a long major and a weak hand. The range is 3–9 HCP. The bids are fairly undisciplined. Not vulnerable, a 5-card suit is common; vulnerable, a 5-card suit is a surprise and a 7-card suit is possible. Many 9-point hands with a 6-card suit are opened at the 1-level instead.
A new suit by responder is natural and forcing. A raise of opener's major is preemptive, meant to take away bidding room, not to invite. A jump to 4 of the major is to play.
The 2NT response is a mixed raise. It shows a good fit for opener's major with constructive-plus values, more than a simple preemptive raise. It is not an asking bid, so opener does not describe strength in steps; opener simply carries on to game with a maximum and passes or signs off with a minimum. A new suit by responder is natural and forcing.
2NT Mixed raise. Good fit, constructive-plus values. Not an asking bid. 3M Preemptive raise. Furthers the preempt, not invitational. 4♣ Preempt RKC. Agrees the major and asks for keycards. 4M To play.
A 4♣ response is Roman Keycard Blackwood for opener's major. Opener answers keycards in steps.
4♦ 0 keycards. 4♥ 1 keycard, no trump queen. 4♠ 1 keycard, with the trump queen. 4NT 2 keycards, no trump queen. 5♣ 2 keycards with the trump queen. Unlikely for a weak two.