function show_menu(){
    addhandler_functie(document.body);
    up_obj = document.getElementById('up');
    down_obj = document.getElementById('down');
    upknop_obj = document.getElementById('upknop');
    downknop_obj = document.getElementById('dropknop');
    down_obj.style.visibility = 'visible';
    up_obj.style.visibility = 'hidden';
    downknop_obj.style.visibility = 'hidden';
    upknop_obj.style.visibility = 'visible';
    return true;
}
function addhandler_functie(n){
    if (n.nodeType == 1){
        n.onmouseup = hide_menu;
    }
    var children = n.childNodes;
    for (var i=0; i < children.length; i++){
        addhandler_functie(children[i]);
    }
}
function hide_menu(){
    up_obj = document.getElementById('up');
    down_obj = document.getElementById('down');
    upknop_obj = document.getElementById('upknop');
    downknop_obj = document.getElementById('dropknop');
    down_obj.style.visibility = 'hidden';
    up_obj.style.visibility = 'visible';
    downknop_obj.style.visibility = 'visible';
    upknop_obj.style.visibility = 'hidden';
    up_obj.onclick = show_menu;
    downknop_obj.onclick = show_menu;
    return true;
}