/**
 * Displays the drop-down menu.
 */
function showMenu(menuName) {
	submenu = document.getElementById(menuName);
	if (submenu != null) {
		submenu.style.visibility = "visible";
	}
}

/**
 * Hides the drop-down menu.
 */
function hideMenu(menuName) {
	submenu = document.getElementById(menuName);
	if (submenu != null) {
		submenu.style.visibility = "hidden";
	}
}