function initAnchorRel() {

    var anchors, length, index, anchor, rel;

    anchors = document.getElementsByTagName("a");
    length = anchors.length;

    for (index = 0; index < length; index++) {

        anchor = anchors.item(index);
        rel = anchor.getAttribute("rel");

        if (rel == "external") {
            anchor.target = "_blank";
            anchor.title = "This link will open a page in a new window.";

        } else if (rel == "pdf") {
            anchor.target = "_blank";
            anchor.title = "This link will open a PDF in a new window.";

        } else if (rel == "xls") {
            anchor.target = "_blank";
            anchor.title = "This link will open an Excel spreadsheet in a new window.";
        }
    }
};

window.onload = initAnchorRel;