Well, raw graphical content is the easy part. A live layout tree that has to be repainted and composited yet intersect with arbitrary layers like an accessibil

Well, raw graphical content is the easy part. A live layout tree that has to be repainted and composited yet intersect with arbitrary layers like an accessibility tree and what would naively be N:N style calculations is completely different architecture. Consider examples where people toy with the concept of replacing the DOM with a canvas but basic things like text selection don't even work anymore.