(document.getElementById) ? dom = true : dom = false;

function hideIt(add) {
  if (dom) {document.getElementById('layer'+add).style.visibility='hidden';}
  if (document.layers) {document.layers["layer"+add].visibility='hide';}
 }
function showIt(add) {
 if (dom) {
  if (document.getElementById('layer'+add).style.visibility=='visible') { hideIt(add); }
  else {document.getElementById('layer'+add).style.visibility='visible'} }

 if (document.layers) {
  if (document.layers["layer"+add].visibility=='show') { hideIt(add); }
  else {document.layers["layer"+add].visibility='show'}  }
 }