function toggle_visibility(id) {
       var divs = document.getElementsByTagName("div");
         for (var i=0; i<divs.length; i++ ) {
           if (divs[i].className.indexOf("section") == -1) continue;
           if (divs[i].getAttribute("id") != id) {
             divs[i].style.display = "none";
           } else {
             divs[i].style.display = "block";
           }
       }
    }