function externalLinksBlank() {
 if (!document.getElementsByTagName) return false;
 var links = document.getElementsByTagName("a");
 if (links.length == 0) return false;
 for (var i=0; i < links.length; i++) {
   var relation = links[i].getAttribute("rel");
   if (relation == "external")
      links[i].target = "_blank";
 }
}