Sé que puedo usar REGEXP en WP_Query así: $query = new WP_Query(array( 'posts_per_page' => -1, 'post_status' => 'publish', 'meta_query' => array( array( 'key' => 'custom_fields', 'value' => 'foo[(][0-9][)]', // with regex stuff 'compare' => 'REGEXP', ), ), )); Pero...