var currentNav;
function setBubVisible(e,visible){
	var innerDn = e.childNodes;
	for ( var j = 0; j < innerDn.length; j++) {
		var innerDnC = innerDn.item(j);
		if (innerDnC.nodeType == 1
				&& (innerDnC.tagName == "ul" || innerDnC.tagName == "UL")) {
			  innerDnC.style.display = visible?"block":"none";
		}
	};
}    

function isContainIn(p,e){
    e = e.parentNode;
    while(e){
       if(e == p){
           return true;
       }
       e = e.parentNode;
    }
    return false;
}
    
function initNavigation() {
	var dn = document.getElementById("dropdown_nav");
    dn.onmousemove = function(event){
    	event = window.event || event;
    	var target = event.srcElement || event.target;
    	if(currentNav){ 
    		if(isContainIn(target,currentNav)){
    			setBubVisible(currentNav,false);
    		}
    	}
    	if(target.className == 'nav_ao'){
    		if(currentNav && target.parentNode != currentNav){
    			setBubVisible(currentNav,false);
    		}
    		currentNav = target.parentNode;
    		setBubVisible(currentNav,true);
    	}
    	event.cancelBubble = true;
     };
      
     document.onmousemove = function(event){
    	 if(currentNav){ 
    		 setBubVisible(currentNav,false);
    	 }
     }
}