Allow region query in Relevanssi search

allow-region.php

// add region query variable

add_filter('query_vars', 'introduce_region_qv');
function introduce_region_qv($qv) {
	$qv[] = 'job_region';
	return $qv;
}

// filter relevanssi based on job_region query

add_filter('relevanssi_modify_wp_query', 'region_tax_query');
function region_tax_query($query) {
	$tax_query = array();
	if (!empty($query->query_vars['job_region'])) {
		$tax_query[] = array(
			'taxonomy' => 'region',
			'field' => 'id',
			'terms' => $query->query_vars['job_region']
		);
	}
	if (!empty($tax_query)) {
		$tax_query['relation'] = 'AND'; // you can also use 'OR' here
		$query->set('tax_query', $tax_query);
	}
	return $query;
}