I claim that an improved option 4 would be: parent { ...parent rules... } @nest { ...nested rules... } by analogy with `try { ... }

I claim that an improved option 4 would be: parent { ...parent rules... } @nest { ...nested rules... } by analogy with `try { ... } catch { ... }` syntax. Looks a lot better than the line noise `} {` thing. An improved option 3 would be to unconditionally require the &. Another alternative would be to stick with Sass syntax but require nested selectors to use :where: parent { ...parent rules... :where(child:pseudo) { ...nested rules... } } and maybe allow :nest(...) as an alias of :where(...), except disallow it at the top level. parent { ...parent rules... :nest(child:pseudo) { ...nested rules... } } Or play a similar weird trick to the original option 3 and only require :where(...)/:nest(...) for selectors that begin with a letter. But that starts to look a lot like option 3. Especially if you always require &, because then & can be used to disambiguate the child:pseudo parsing problem. I'm not familiar with the past discussion of any of this, though.