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