function triggerNav(id) {
    var tohide = document.getElementById(id);
    if (tohide != null) {
        if (tohide.style.visibility == 'visible') {
            tohide.style.visibility = 'hidden';
            tohide.style.display = 'none';
        } else {
            tohide.style.visibility = 'visible';
            tohide.style.display = 'block';
        }
    }
}