function toggle(id){
  if (toggleDisplayByID(id) == "block") 
    openSubMenu = id;
  else 
    openSubMenu = false;
}

function toggleDisplay(node){
  if (node.style.display == 'none'){ 
    node.style.display = '';
  } else {
    node.style.display = 'none';
  }
  return node.style.display;
}

function toggleDisplayByID(id){
  node = document.getElementById(id);
  return toggleDisplay(node);
}