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;