Black 4 is perhaps questionable. Black chooses 4 instead, to make more of the position. This lets us out of the Magic Sword rut . It is one thing to realise that context changes everything in Go, something else again to implement that flexibility. White has allowed Black the corner, and needs an honest move at one of the 'x' points to make shape round here.
Innovation rolls on, however, especially in the Korean powerhouse of goal-directed research.
Play White 1 first, presumably getting the answer 2, before coming in at 3. The intention is to mix it after Black plays 4. The warlike 5 and 7 are a concerted attempt to isolate Black's corner, the heart, as you will recall, of Black's intended grand framework. Black can't go down this road with 8. White 9 sets up a well-known tactic for confinement.