// start handling visibility
targetView.visibility
    .changed { state in
        switch state {
        case .visible:
            // visible process here
        case .invisible:
            // invisible process here
    }
}

// stop handling visibility
targetView.visibility.invalidate()

targetView.visibility
    .setConfig { config in
        config.timeInterval = 1.0
        config.intersectionRatio = 0.8
        config.transparencyRatio = 0.5
    }
    .changed { state in
        ...
    }