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.target = "_blank";
     }
    }
    window.onload = externalLinks;