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.getAttribute("rel") == "ext")) 
        {
            anchor.target = "_blank";
        }
    }
}

window.onload = externalLinks;