Are you sure about that? When I read quotes like "web content (JavaScript, HTML, layout, etc) lives in a separate process from the application UI", that conjures images of a rather drastic and fundamental change. I'm not sure how you'd achieve that with just a new API layer.
Yes, I'm sure. The same core rendering engine, known as WebCore, is shared between both WebKit1 and WebKit2 on OS X. WebKit1 is used by most applications that use a WebView to display web content, while WebKit2 is used by Safari. The different API layers set up different delegate callbacks for WebCore so that they can tweak the behavior to fit their architecture (single process vs separate web and UI processes).
