window.onload = externalLinks;

function externalLinks() {

if (!document.getElementsByTagName) return;

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";
	}

}