Given the very heartening news that infinite-lookahead is viable in Chrome, I'd like to try and revisit one of our syntax changes caused by Nesting.

In the original version of the spec, you had to start a selector with &, so to handle the case where you want to add a type selector, we relaxed the restriction that a type selector had to be the first thing in a compound selector. This allowed &div to work, tho div& was theoretically okay (in cases like @nest div&).

In the current version of the spec, you still can't start a selector with an ident, so &div is still the right way to spell things most of the time (but again, still okay in theory to do the other way, like .foo div&).

Neither of these restrictions will apply anymore if #7961 goes thru. Which is good, because &div is terrible for Sass.

Sass essentially uses text concatenation for its nesting feature. If you write .foo { &div {...}} in Sass, it generates a .foodiv {...} rule - a single larger class selector. In CSS Nesting, this is instead equivalent to div.foo {...} - a type selector plus a class selector.

This mismatch in syntax was always going to be an enormous pain for Sass to migrate to CSS Nesting (possibly a straight-up blocker, requiring Sass users to explicitly opt into CSS Nesting instead), but when other factors made &div the preferred form, I accepted that it was just one of those painful situations that'll be worth it in the long term.

But given #7961, there's no longer any reason to prefer &div over div&. So we can simultaneously (a) remove a syntax change, preserving the original syntax of Selectors that has been stable for a long time, and (b) make Sass's task of migrating to CSS Nesting natively massively easier (along with any other preprocessor that has a similar feature, but I'm familiar with Sass's syntax here).

I've talked with @andruud about this and he's dropping a Use Counter into Chrome preemptively, to make sure we'll actually be able to make this change. (Since we're shipping the current Nesting spec in Chrome 112 which is just now releasing to Stable.)

/cc @nex3