document.onkeydown = keyDown;
var currentLayerId = null;

function showLayer(layerId)
{
  if (currentLayerId != null)
    closeLayer();
    
  layer = document.getElementById(layerId);

  // si on utilise les dimentions a la mode netscape
  if (window.innerHeight)
  {
    layer.style.top = window.pageYOffset+window.innerHeight/2-layer.offsetHeight/2;
    layer.style.left = window.pageXOffset+window.innerWidth/2-layer.offsetWidth/2;
  }
  // sinon, on utiliser les dimentions a la mode IE
  else
  {
    layer.style.top = document.body.scrollTop+document.body.clientHeight/2-layer.clientHeight/2;
    layer.style.left = document.body.scrollLeft+document.body.clientWidth/2-layer.clientWidth/2;
  }
  
  layer.style.visibility='visible';
  currentLayerId=layerId;
}

function closeLayer ()
{
  if (currentLayerId == null)
    return
    
  document.getElementById(currentLayerId).style.visibility='hidden';
  modifyIsOpen=false;
  currentLayerId=null;
}

function keyDown(evenement)
{
  // on charge le keyCode ... a la mode netscape ou IE selon la situation ...
  if (window.event)
    var code=window.event.keyCode; // mode IE
  else
    var code = evenement.keyCode; // mode netscape
    
  if (code == 27)
     closeLayer();
}