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;