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;