// (c) 2001 Douglas Crockford
  // 2001 June 3
  // The -is- object is used to identify the browser.  Every browser edition
  // identifies itself, but there is no standard way of doing it, and some of
  // the identification is deceptive. This is because the authors of web
  // browsers are liars. For example, Microsoft's IE browsers claim to be
  // Mozilla 4. Netscape 6 claims to be version 5.
  
  var is = {
      ie:      navigator.appName == 'Microsoft Internet Explorer',
      java:    navigator.javaEnabled(),
      ns:      navigator.appName == 'Netscape',
      ua:      navigator.userAgent.toLowerCase(),
      version: parseFloat(navigator.appVersion.substr(21)) ||
               parseFloat(navigator.appVersion),
      win:     navigator.platform == 'Win32'
  }
  is.mac = is.ua.indexOf('mac') >= 0;
  if (is.ua.indexOf('opera') >= 0) {
      is.ie = is.ns = false;
      is.opera = true;
  }
  if (is.ua.indexOf('gecko') >= 0) {
      is.ie = is.ns = false;
      is.gecko = true;
  }