function showSection(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";  
     }
   } 
 }
 
 
function prepareInternalnav() {
  if (!document.getElementsByTagName) return false;
  if (!document.getElementById) return false;
  if (!document.getElementById("internalnav")) return false
  var nav = document.getElementById("internalnav");
  var links = nav.getElementsByTagName("a");
  for (var i=0; i<links.length; i++) {
    var sectionId = links [i].getAttribute("href").split("#")[1];
    if (!document.getElementById(sectionId)) continue;
    document.getElementById(sectionId).style.display = "none";
    links[i].destination = sectionId;
    links[i].onclick = function() {
      showSection(this.destination);
      return false;
    }
  }
}

addLoadEvent(prepareInternalnav);