[JonathonW]

I'm sure there's a reason here that I'm not seeing, but it feels like it's being different for the sake of being different to me-- requiring `&` even in the simple case where you're combining them with the descendant combinator (plain space), but then also requiring `@nest` in any situation where `&` is not at the start of each selector.

SASS takes the opposite approach-- there's an implicit `&` at the beginning if you don't specify it elsewhere, and it can appear anywhere (i.e. the example `:not(&)` does not have to have anything like the `@nest` syntax in SASS).

[ihuman]

There's an explanation in section 2, in the green box that says "Why can’t everything be directly nested?"