private async void BtnGetMetadata_Click(object sender, RoutedEventArgs e)
        {
            string urls = UrlBox.Text;
            List <DocumentClosure> documentCollection = new List <DocumentClosure>();

            foreach (var url in urls.Split(new string[] { Environment.NewLine }, StringSplitOptions.None))
            {
                Document        document        = semanticsSessionScope.GetOrConstructDocument(new ParsedUri(url));
                DocumentClosure documentClosure = document.GetOrConstructClosure(semanticsSessionScope.MetadataServicesClient);

                documentCollection.Add(documentClosure);
            }

            foreach (var documentClosure in documentCollection)
            {
                documentClosure.Continuations += this.MetadataDownloadComplete;
                documentClosure.GetMetadata();
            }
        }