Hello webkit-dev,

I've been working on a new header called Origin-Isolation, which is a way of allowing origins  to opt-out of using document.domain and cross-origin sharing of WebAssembly.Module, and thus allowing the browser to put them into an origin-keyed agent cluster instead of a site-keyed one. This could in turn allow the browser to make better behind-the-scenes decisions for process isolation, or other resource allocation decisions, since sites no longer have any ways to synchronously communicate cross-origin.

Relevant links:

* Explainer: https://github.com/WICG/origin-isolation

* HTML spec PR: https://github.com/whatwg/html/pull/5545

* Test suite: https://github.com/web-platform-tests/wpt/tree/master/origin-isolation

* Gecko "worth prototyping" standards position: https://mozilla.github.io/standards-positions/#domenic-origin-isolation

A natural question one might ask is how this relates to COOP+COEP? The explainer has that covered: https://github.com/WICG/origin-isolation#coop--coep

Thanks for your time!

-Domenic