function externalLinks() {

  if (!document.getElementsByTagName) return;
  
  var anchors = document.getElementsByTagName("a");
  for (var i=0; i<anchors.length; i++) {
    var anchor = anchors[i];
    var relvalue = anchor.getAttribute("rel");
    
    if (anchor.getAttribute("href")) {
      var external = /external/;
      var relvalue = anchor.getAttribute("rel");
      if (external.test(relvalue)) { anchor.target = "_blank"; }
    }
  }
}
window.onload = externalLinks;