protected function loadBackgroundHash(array $hash)
    {
        $hash = array_merge(
            array(
                'title' => null,
                'keyword' => 'Background',
                'line' => 0,
                'steps' => array(),
            ),
            $hash
        );

        $steps = $this->loadStepsHash($hash['steps']);

        return new BackgroundNode($hash['title'], $steps, $hash['keyword'], $hash['line']);
    }