I'm not sure if we disagree or not. Later this document says "The Reactive Streams API prescribes that all processing of elements (`onNext`) or termination signals (`onError`, `onComplete`) happens outside of the execution stack of the `Publisher`." This sounds as if it would refer to some previous description and explain it further. With `asynchronous` gone it seems that there's nothing in this paragraph that would actually spec it. (Maybe it's just a matter of wording.)