Complex sentence: In other words, when the needed rotation of the fluid exceeds the maximum achievable with an oblique attached shock, the shock detaches from the body; hence beyond the shock the flow-field is subsonic so the boundary condition can be respected at the stagnation point.
Split into simpler sentences: In other words, when the needed rotation of the fluid exceeds the maximum achievable rotation angle for an oblique attached shock, the shock detaches from the body. Downstream of the shock, the flow-field is subsonic, and the boundary condition can be respected at the stagnation point.