function Is() {
  var agent = navigator.userAgent.toLowerCase();
  this.major = parseInt(navigator.appVersion);
  this.minor = parseFloat(navigator.appVersion);
  this.ns = ((agent.indexOf('mozilla')!=-1) && ((agent.indexOf('spoofer')==-1) &&
(agent.indexOf('compatible') == -1)));
  this.ns2 = (this.ns && (this.major == 3));
  this.ns3 = (this.ns && (this.major == 3));
  this.ns4b = (this.ns && (this.minor < 4.04));
  this.ns4 = (this.ns && (this.major >= 4));
  this.ie = (agent.indexOf("msie") != -1);
  this.ie3 = (this.ie && (this.major == 2));
  this.ie4 = (this.ie && (this.major >= 4));
  this.op3 = (agent.indexOf("opera") != -1);
  this.win = (agent.indexOf("win")!=-1);
  this.mac = (agent.indexOf("mac")!=-1);
  this.unix = (agent.indexOf("x11")!=-1);
}