Relevanssi has the option to boost the weight of results which match all words of the search query. So when searching for “word1 word2” and a post’s title is “word1 word2 word3”, that post will appear extra high in the results, rather than simply treating it as a hit with 2 matches (1 for each word). This exact match boost only supports hits in the post title and post description by default. In some cases it can be useful to also be applied to meta data, since it’s quite common for a site to save additional types of content as metadata.

Based on the original function that works on title/description, I wrote an adaptation that applies to metadata:

// Add weight to exact matches in meta values
add_filter( 'relevanssi_results', function( $results ) {

	// Search term
	$query = strtolower( get_search_query() );

	// List of results as post-id => weight
	foreach ( $results as $post_id => $weight ) {

		// Boost exact meta value hits
		foreach ( get_post_meta( $post_id ) as $meta_key => $meta_values ) {
			foreach ( $meta_values as $meta_value ) {
				if ( stristr( $meta_value, $query ) != false ) {
					$results[ $post_id ] = $weight * 100;
				}
			}
		}

	}

	return $results;

} );