Add_Custom_Fields_To_Search::cf_search_join( string $join )

		public function cf_search_join( $join ) {
			global $wpdb;

			if ( ! is_search() || $this->is_media_library() ) {
				return $join;
			}

			// join to search post meta values like year, make, model, trim, etc.
			$join .= " LEFT JOIN $wpdb->postmeta searchmeta ON $wpdb->posts.ID = searchmeta.post_id ";

			// these joins are so taxonomy terms like Sport Utility Vehicle => suv are included.
			$join .= "LEFT JOIN $wpdb->term_relationships tr ON $wpdb->posts.ID = tr.object_id "
				. "INNER JOIN $wpdb->term_taxonomy tt ON tt.term_taxonomy_id = tr.term_taxonomy_id "
				. "INNER JOIN $wpdb->terms t ON t.term_id = tt.term_id ";

			return $join;
		}