// Make sure the function runs.
window.onload = documentLoad;

// Selects the first field in the first active form for input.
function documentLoad()
{
   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";
        }
   }
}