anchor.diff:  
   _IE Protect Mode_ will cause `window.open()` return `null` as:
   
  -[quote, https://msdn.microsoft.com/library/ms536651(v=vs.85).aspx]
  +[quote]
   ____
   Internet Explorer 7 on Windows Vista: Opening a new window from an application (other than the Internet Explorer process) may result in a null return value. This restriction occurs because Internet Explorer runs in protected mode, by default. One facet of protected mode prevents applications from having privileged access to Internet Explorer when that access spans process boundaries. Opening a new window by using this method generates a new process. For more information about protected mode, see https://msdn.microsoft.com/zh-cn/library/bb250462(v=vs.85).aspx[Understanding and Working in Protected Mode Internet Explorer]. This commonly occurs for applications that host the WebBrowser control.
   ____
  
positive.code: * (WPAD) Proxy Script. If the user’s proxy configuration is “Automatically detect settings” or “Use automatic configuration script” inside Tools > Internet Options > Connections > LAN Settings, the browser will run the FindProxyForUrl function in the specified WPAD proxy configuration script to determine which proxy should be used for each request. If the script returns "DIRECT", the browser will bypass the proxy and the site will be mapped into the Local Intranet Zone. When mapping a URL to a Zone, URLMon will call the FindProxyForUrl function to determine if the bypass rule applies. One interesting twist is that the proxy script may itself call dnsResolve to get a site’s IP address and use that information as a part of its determination.
  ____
  
  
negative.code: 
  [source,javascript]
  ----
  service.popup = window.open(url, pendingRequestKey, optionsString); //// <1>
  
  if (service.popup && !service.popup.closed) {
    service.popup.focus();
  