protected function toString()
    {
        if ($this->rendered !== null) {
            return $this->rendered;
        }

        if (is_callable($this->callback)) {
            try {
                return $this->rendered = $this->invokeCallable($this->callback, $this->callbackArguments);
            } catch (\Exception $e) {
                trigger_error($e->getMessage(), E_USER_NOTICE);
            }
        }

        return $this->content ?: '';
    }