Reference IDL [Exposed]

[leobalter]

One approach we can take here is to reference IDL [Exposed] as potential properties the host can provide to a realm, and select from those ones which have been adopted by multiple host types. In addition, not allowing access to this will put pressure on TC39 to re-standardize things that are already standard, and used. We already reference external specifications.

Speaking with @annevk, there was a proposal for something like [Exposed=*] to identify truly universal apis, though that hasn't materialized yet.

Originally posted by @codehag in #284 (comment)

[leobalter]

I like this idea, but I need more information on how to do it.

I'm opening this issue to avoid crossed discussions from #284.

[littledan]

I agree that we should use [Exposed] editorially to expose web APIs to Realms. We will need to do a lot of plumbing in WebIDL to specify how this will actually work. cc @Ms2ger

[erights]

I want to be explicit that, at this time, I do not agree or disagree. I need to understand this first.

[Ms2ger]

Plumbing should be pretty limited; own exposure set would need to be updated to allow a particular value for Realms and exposed should interpret it, and then define the global property references should be called somewhere from the host when creating the Realm. Interfaces that opt in to being exposed in Realms would then need a change like

-[Exposed=(Window,Worker)]
+[Exposed=(Window,Worker,Realm)]
 interface TextDecoder {

[caridy]

closing this in favor of #398