Reasoning: I do not see much sense in the use of additional brackets (option 3), since "&" already serves as a separator. I also do not see much sense in the use of the more verbose "@nest" (option 2), since conventional selector syntax uses single-character keywords already and there is no real parallel to things like "@media" or "@page" (as this isn't related to rendering and formats).
Reasoning: I do not see much sense in the use of additional brackets (option 3), since "&" already serves as a separator. I also do not see much sense in the use of the more verbose "@nest" (option 2), since conventional selector syntax uses single-character keywords already and there is no real parallel to things like "@media" or "@page" (as this isn't related to rendering and formats).