//<a rel="blank" href="http://www.google.com/">別ウィンドウで開きます。</a>
function targetBlank() {
	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 nofollow") || (anchor.getAttribute("rel") == "nofollow external") || (anchor.getAttribute("rel") == "external")))
			anchor.target = "_blank";
		}
}
window.onload = targetBlank;