Elastica\Multi\Search::_getSearchData PHP Method

    protected function _getSearchData(BaseSearch $search)
    {
        $header = $this->_getSearchDataHeader($search);
        $header = empty($header) ? new \stdClass() : $header;
        $query = $search->getQuery();
        // Keep other query options as part of the search body
        $queryOptions = array_diff_key($search->getOptions(), array_flip(self::$HEADER_OPTIONS));
        $data = JSON::stringify($header) . "\n";
        $data .= JSON::stringify($query->toArray() + $queryOptions) . "\n";
        return $data;
    }