Elastica\Multi\Search::_getSearchDataHeader PHP Method

    protected function _getSearchDataHeader(BaseSearch $search)
    {
        $header = $search->getOptions();
        if ($search->hasIndices()) {
            $header['index'] = $search->getIndices();
        }
        if ($search->hasTypes()) {
            $header['types'] = $search->getTypes();
        }
        // Filter options accepted in the "header"
        return array_intersect_key($header, array_flip(self::$HEADER_OPTIONS));
    }