function popup(url) {
    var breite = 200;
    var hoehe = 50;
    var links = (screen.width-breite)/2;
    var oben = (screen.height-hoehe)/2;
    Fenster = window.open(url ,"Fenstername", "width="+breite+",height="+hoehe+",left="+links+",top="+oben+",resizable=no");
    Fenster.focus();
}

function toggleTreeKlappe(elm, subid) {
    sub = document.getElementById(subid);
    if(sub.style.display != "block") {
        elm.value = "^";
        sub.style.display="block";
    } else {
        elm.value = "v";
        sub.style.display="none";
    }   
}