anchor.diff:    /// The engine that powers Edge.
     edge,
   
  +  /// The engine that powers Internet Explorer 11.
  +  ie11,
  +
     /// We were unable to detect the current browser engine.
     unknown,
   }
  
positive.code: 
    // Assume blink otherwise, but issue a warning.
    print('WARNING: failed to detect current browser engine.');
  
    return BrowserEngine.unknown;
  }
  
  
negative.code: 
  BrowserEngine _detectBrowserEngine() {
    final String vendor = html.window.navigator.vendor;
    final String agent = html.window.navigator.userAgent.toLowerCase();
    if (vendor == 'Google Inc.') {
      return BrowserEngine.blink;
    } else if (vendor == 'Apple Computer, Inc.') {
      return BrowserEngine.webkit;
    } else if (agent.contains('edge/')) {
      return BrowserEngine.edge;
    } else if (agent.contains('trident/7.0')) {
      return BrowserEngine.ie11;
    } else if (vendor == '' && agent.contains('firefox')) {
      // An empty string means firefox:
      // https://developer.mozilla.org/en-US/docs/Web/API/Navigator/vendor
      return BrowserEngine.firefox;
  