Html: Cross-Origin-Opener-Policy: provide a clearer spec.

[empijei]

Currently COOP is being implemented in Firefox and there are plans to add this to all other major browsers.

This feels like we got to the point where a clear specifications with intentions, thread model and mechanics should be put together.

I'm mostly interested in

• avoiding different behaviors in different browsers
• state threat model and intentions clearly so that it is easy to reason about it

Currently there is a tentative spec for the algorithm and a rather long dicussion that contains all the step that this proposal went through.

I read all that to try and understand what the policy should accomplish and I think I got it, but I also think this should be easier for newcomers, users and implementers to tackle and understand.

/cc @arturjanc @domenic @rniwa @annevk @csreis @mystor

[annevk]

I agree that it'd be good to add this. I'm personally focusing on

• Iterating on the processing model gist pointed to above
• Tests

so it'd be great if someone were willing to pick this up.

[camillelamy]

@hemeryar, @ParisMeuleman or myself will pick this up once we're done with Chrome's implementation of COOP.

[camillelamy]

I have a draft PR at https://github.com/whatwg/html/pull/5334 that takes https://gist.github.com/annevk/6f2dd8c79c77123f39797f6bdac43f3e and merges it into the spec.