protocol WebkitBrowsable: WKUIDelegate {
    var webView: WKWebView { get }
    var progressView: UIProgressView { get }

    var URL: NSURL? { get }
    var cachePolicy: NSURLRequestCachePolicy { get }
    var timeoutInterval: NSTimeInterval { get }

    init(withURL URL: NSURL?, withCachePolicy cachePolicy: NSURLRequestCachePolicy?, withTimeoutInterval timeoutInterval: NSTimeInterval?)
}