var nb_nav_down = 3;

function hideAll(){
	for(i = 1; i <= nb_nav_down; i++){
		document.getElementById('nav_down0'+i).style.visibility = 'hidden';
	}
	return true;
}
function show(num){
	if(hideAll()){
		document.getElementById('nav_down0'+num).style.visibility = 'visible';
	}				
}
function bodyOnClick(){ 
  hideAll(); 
}
		  
function roll(item){	
	var srcDep= document.images[item].src;
	
	if (srcDep.search("_off")!=-1) {
		var srcFin=srcDep.replace(/_off/,"_on");		
	} else {
		var srcFin=srcDep.replace(/_on/,"_off");
	}
	document.images[item].src= srcFin;	
}