Adam Klein

What about two different observers in the same realm? I think you'd want them to share records if possible (to avoid unnecessary record allocations).

There can be multiple `Object.observe` functions per object, just as there can be observer functions from multiple realms. I'm not clear on how @domenic's suggestion gives a clear answer about...

Which callback function? Objects only have one notifier. Are you suggesting we give them multiple notifiers, one per realm that's observing them?

Aha! Multiple notifier objects seems like it might be a bigger change...

See whatwg/webidl#937 for the existing issue against WebIDL asking how to specify this.