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") == "newwindow") 
    anchor.target = "_blank"; 
} 
} 
window.onload = externalLinks;