// match all instances of 'external'
function externalLinks() {
     if (!document.getElementsByTagName) return;
     var anchors = document.getElementsByTagName("a");
     for (var i=0; i<anchors.length; i++) {
          var pattern = /external/i;
          var anchor = anchors[i];
          var relative = anchor.getAttribute("rel");
          if (anchor.getAttribute("href") && pattern.test(relative)) {
               anchor.target = "_blank";
          }
     }
}

document.observe("dom:loaded", function() {
	externalLinks();
});