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;