function relTags() {

   if (document.getElementsByTagName) {
	
	   var anchors = document.getElementsByTagName( "a" );
	   
	   for (var loop = 0; loop < anchors.length; loop++) {
	       
	       var anchor = anchors[loop];
	       if (anchor.getAttribute("href") && anchor.getAttribute("rel") == "external") {
	           anchor.target = "_blank";
	       }
	   }
	}
}

window.onload = function() {

	relTags();

}