document.onclick = function(e)
{
  var target = e ? e.target : window.event.srcElement;

  while (target && !/^(a|body)$/i.test(target.nodeName))
  {
    target = target.parentNode;
  }

  if (target && target.getAttribute('rel')
      && target.rel == 'external')
  {
    var external = window.open(target.href);

    return external.closed;
  }
}

function externalLinks() { 
 if (!document.getElementsByTagName) return; 
 var anchors = document.getElementsByTagName("a"); 
 for (var i=0; i<anchors.length; i++) { 
   var anchor = anchors[i]; 
   if (anchor.getAttribute("href") && 
       anchor.getAttribute("rel") == "external") 
     anchor.title = "link opens in new window"; 
 } 
} 
window.onload = externalLinks;