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";   
    }   
}