function target_blank() {
	if (!document.getElementsByTagName) {
		return;
	}
	var anchors = document.getElementsByTagName("a");
	var i;
	var enlace;

	for (i = 0; i < anchors.length; i++) {
		var enlace = anchors[i];
		if (enlace.getAttribute("href") && enlace.getAttribute("rel") == "external") {
			enlace.target = "_blank";
		}
	}

}

function attachEventListener(target, eventType, functionRef, capture) {
    if (typeof target.addEventListener != "undefined") {
        target.addEventListener(eventType, functionRef, capture);
    } else if (typeof target.attachEvent != "undefined") {
        target.attachEvent("on" + eventType, functionRef);
    } else {
        return false;
    }

    return true;
}

attachEventListener(window, "load", target_blank, false);