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";
    }
  }
}