function initializeDropDownMenu(){
	// get 'navbar' element
	var navbar=document.getElementById('navbar');
	if(!navbar){return};

	// get all menu items
	var menuitems=navbar.getElementsByTagName('li');
	if(!menuitems){return};
	for(var i=0;i<menuitems.length;i++){
		// assign 'over' class attribute to each menu item on 'mouseover'
		menuitems[i].onmouseover=function(){
			this.className+=' over';
		}
		
		// remove 'over' class attribute to each menu item on 'mouseout'
		menuitems[i].onmouseout=function(){
			this.className=this.className.replace(' over','');
		}
	
	}
	
}

// initialize drop-down menu when web page is loaded
window.onload=function(){
	if(document.all&&document.getElementById&&document.getElementsByTagName){
		initializeDropDownMenu(); 
	}
}