public function isDisplayable() {
        $displayable = $this->enable && $this->visible;
        if (true === $displayable) {
            return true;
        }
        foreach ($this->getNodes() as $current) {
            if (false === ($current instanceof AbstractNavigationNode)) {
                continue;
            }
            if (true === $current->isDisplayable()) {
                return true;
            }
        }
        return $displayable;
    }