Must you keep all cards when a stays-in-play effect is used, or can you choose which to keep?

Question

Accepted Answer

You cannot choose only some. The effect keeps all the cards it covers. Using it is optional, but if you choose to use it, you must do as much as possible.

Kingdom Legacy: Feudal Kingdom

Must you keep all cards when a stays-in-play effect is used, or can you choose which to keep?