// rozwijanie submenu
function submenu() {
	var subMenu = document.getElementById('mainMenu').getElementsByTagName('li');
	for (i=0; i<subMenu.length; i++){
		if (subMenu[i].className == "subMenu"){
			subMenu[i].onclick = function (){
				var subMenuVisibility = this.getElementsByTagName('ul')[0];
				if (subMenuVisibility.style.display == "block") {
					subMenuVisibility.style.display = "none";
				}
				else {
					subMenuVisibility.style.display = "block";
				}
			}
		}
	}
}

//onload
window.onload = function (){
	submenu();
}