function a_external() {
   var a,l,i,d=document;
   if (!d.getElementsByTagName) return;
   a = d.getElementsByTagName("a");
    for (i=0;i<a.length;i++) {
         l = a[i];
         if (l.getAttribute("href") && l.getAttribute("rel") == "external") l.target = "_blank";
   }
}
window.onload = a_external;