public function setFiles($filenames)
    {
        if ($this->isReference()) {
            throw $this->tooManyAttributes();
        }
        if (!empty($filenames)) {
            $tok = strtok($filenames, ", \t\n\r");
            while ($tok !== false) {
                $fname = trim($tok);
                if ($fname !== "") {
                    $this->filenames[] = $tok;
                }
                $tok = strtok(", \t\n\r");
            }
        }
    }