}

        private ActivationFrame nextFrame(String property) {
            return new ActivationFrame(property, Optional.empty());
        }

        private <P> ActivationFrame nextFrame(String property, Function<P, InputLocationTracker> child) {
            @SuppressWarnings("unchecked")
            final Optional<P> parent = (Optional<P>) stk.peek().parent;
            return new ActivationFrame(property, parent.map(child));