function Is() {
    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.ns6    = (this.ns && (this.major     >=    5));
    this.ns4   = (this.ns && (this.major      >=    4) &&
					!(this.ns6));   
    this.ie    = (agent.indexOf("msie")       !=   -1);
    this.ie4   = (this.ie && (this.major      ==    4) &&
                 (agent.indexOf("msie 5.0")   ==   -1) &&
				 (agent.indexOf("msie 5.5")   ==   -1));
    this.ie5   = (this.ie && (this.major      ==    4) &&
                 (agent.indexOf("msie 5.0")   !=   -1));
    this.ie55  = (this.ie && (this.major      ==    4) &&
                 (agent.indexOf("msie 5.5")   !=   -1));
	this.mac   = (navigator.platform.indexOf("Mac") != -1)
}

	var is = new Is();
	
	if (is.ie4 ||is.ie5 || is.ie55) { 
		doc = 'document.all.';
		styl = '.style';
		on = "'visible'";
		off= "'hidden'";
		htm = ".document"
	} else
	if (is.ns4) {
		doc = 'document.layers.';
		styl = '';
		htm="";
		on = "'show'";
		off = "'hide'";
	} else
	if (is.ns6) {
		doc = "document.getElementById('";
		styl = "').style";
		on = "'visible'";
		htm="";
		off= "'hidden'";
	} else { 
		alert("Warning: This page works not properly with the browser you are using. We advise to use the Internet Explorer 5.x");
	}