public void Update()
        {
            lock (TestPage)
            {
                TestPage.Clear();
                TestPage.AddEntry("<h1> Video content delivery test: </h1><br>");
                TestPage.AddEntry("<br><iframe src=\"who.mp4\" width=\"100%\" height=\"300\" style=\"border:1px solid black;\">\r\n<br></iframe>");

                TestPage.AddEntry($"<br><br>It is {DateTime.Now}.");
                TestPage.AddEntry(
                    $"Thread pool threads: {ThreadPool.ThreadCount}, pending: {ThreadPool.PendingWorkItemCount}, completed: {ThreadPool.CompletedWorkItemCount}");
                if (PoemIndex < _poem.Length)
                {
                    TestPage.AddEntry(_poem[PoemIndex++]);
                }
                else
                {
                    PoemIndex = 0;
                }
            }
        }