MailChimp: Grow sales with Customer Journey Smarts
Šime Vidas with the lowdown on what these pseudo-selectors are and why they will be useful:
:is() is to reduce repetition¹ of parts of comma-separated selectors.
:where() is the same, but nothing inside it affects specificity. The example of wrapping :where(:not()) is really great, as now there is a way to use :not() without bumping up the selector weight in a way you very likely don’t want.
This is something that CSS preprocessors are good at (via nesting). Another nice little example of community-built tech pushing forward and native tech coming up later to help once the idea is fleshed out.