     
     public var customHTTPHeaderFields: [String : String]?
     
-    private var _validSchemes = Set<String>(["http", "https", "tel", "file"])
+    private var _validSchemes = Set<String>(["http", "https", "file"])
     
     private var progressContext = 0
     private var pageTitleContext = 0

            let script = """
                var script = document.createElement('meta');
                script.name = 'viewport';
                script.content=\"width=device-width, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0, user-scalable=no\";
                document.getElementsByTagName('head')[0].appendChild(script);
            """
            let scaleScript = WKUserScript(source: script, injectionTime: .atDocumentEnd, forMainFrameOnly: false)

    }
    
    fileprivate func launchExternalApp(url: URL) {
        let systemSchemes = ["tel", "sms", "mailto"]
        if let scheme = url.scheme,
            systemSchemes.contains(scheme) {
            if #available(iOS 10.0, *) {
                UIApplication.shared.open(url)
            } else {
                UIApplication.shared.openURL(url)
            }
        } else {
            let alertController = UIAlertController(title: "Leave current app?", message: "This web page is trying to open an outside app. Are you sure you want to open it?", preferredStyle: .alert)
            let cancelAction = UIAlertAction(title: "Cancel", style: .cancel, handler: nil)
            alertController.addAction(cancelAction)
            let openAction = UIAlertAction(title: "Open App", style: .default) { (action) in
                if #available(iOS 10.0, *) {
                    UIApplication.shared.open(url)
                } else {
                    UIApplication.shared.openURL(url)
                }
            }
            alertController.addAction(openAction)
            UIApplication.shared.keyWindow?.rootViewController?.present(alertController, animated: true)
        }
    }
}

