//change class name
function changeClassName(elementname, classnamedefault, classnamesecondary, evt) {
    
    //get element
    var element = document.getElementById(elementname);

    //set class name
    if (element.className == classnamedefault) element.className = classnamesecondary; else element.className = classnamedefault;
    
    //disable bubble-up
    var e=(evt)?evt:window.event;    
    if (window.event) e.cancelBubble=true; else e.stopPropagation();
};