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";
 }

 var forms = document.getElementsByTagName("form");
 for (var i=0; i<forms.length; i++) {
   var form = forms[i];
   if (form.getAttribute("action") &&
       form.getAttribute("rel") == "external")
     form.target = "_blank";
 }
}
window.onload = externalLinks;