private function getMergedOptions(array $options)
    {
        $options = array_merge(
            $this->getDefaultOptions(),
            $options
        );

        if (isset($options['formats'])) {
            $options['formats'] = self::mergeFormats($this->getDefaultFormats(), $options['formats']);
        } else {
            $options['formats'] = $this->getDefaultFormats();
        }

        if (is_null($options['line_ending'])) {
            $options['line_ending'] = $options['type'] === 'html' ? '<br/>' : "\n";
        }

        if (is_null($options['indentation'])) {
            $options['indentation'] = $options['type'] === 'html' ? '&nbsp;&nbsp;&nbsp;&nbsp;' : '    ';
        }

        // `parts_newline` requires `clause_newline`
        $options['parts_newline'] &= $options['clause_newline'];

        return $options;
    }