function externallinks() {
    var ls = document.getElementsByTagName('a');
    for (var i = 0; i < ls.length; i++) {
        if (ls[i].getAttribute('rel') == 'external') {
            ls[i].title += '(opens in new window)';
            ls[i].onclick = function() { window.open(this.href); return false }
        }
    }
}

window.onload = function() {
    if (!document.getElementById && !document.createTextNode) { return; }
    externallinks();
}