void webAlert(string $msg[, $url]);

$modx->webAlert("hello world", "http://www.google.com"]);

function webAlert($msg, $url= "") {
        $msg= addslashes(mysql_escape_string($msg));
        if (substr(strtolower($url), 0, 11) == "javascript:") {
            $act= "__WebAlert();";
            $fnc= "function __WebAlert(){" . substr($url, 11) . "};";
        } else {
            $act= ($url ? "window.location.href='" . addslashes($url) . "';" : "");
        }
        $html= "<script>$fnc window.setTimeout(\"alert('$msg');$act\",100);</script>";
        if ($this->isFrontend($html))
            $this->regClientScript($html);
        else {
            echo $html;
        }
    }