Does the code from the ActionViewController in the Extension folder act as the intermediary between Safari and iOS?

I am have difficulty understanding what purpose these pieces of code serve in creating the extension. More specifically the viewDidLoad() func and the done() func.

class ActionViewController: UIViewController {
    @IBOutlet var script: UITextView!

    var pageTitle = ""
    var pageURL = ""

    override func viewDidLoad() {
        super.viewDidLoad()

        navigationItem.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: .done, target: self, action: #selector(done))

        if let inputItem = extensionContext?.inputItems.first as? NSExtensionItem {
            if let itemProvider = inputItem.attachments?.first {
                itemProvider.loadItem(forTypeIdentifier: kUTTypePropertyList as String) { [weak self] (dict, error) in 
                    guard let itemDictionary = dict as? NSDictionary else {
                        return }
                    guard let javaScriptValues = itemDictionary[NSExtensionJavaScriptPreprocessingResultsKey] as? NSDictionary else { return }
                    self?.pageTitle = javaScriptValues["title"] as? String ?? ""
                    self?.pageURL = javaScriptValues["URL"] as? String ?? ""

                    DispatchQueue.main.async {
                        self?.title = self?.pageTitle
                    }
                }
            }
        }

    }

    @IBAction func done() {
        let item = NSExtensionItem()
        let argument: NSDictionary = ["customJavaScript": script.text]
        let webDictionary: NSDictionary = [NSExtensionJavaScriptFinalizeArgumentKey: argument]
        let customJavaScript = NSItemProvider(item: webDictionary, typeIdentifier: kUTTypePropertyList as String)
        item.attachments = [customJavaScript]
        extensionContext?.completeRequest(returningItems: [item])

    }

}