id). * @return array */ public function delete_meta( &$data, $meta ); /** * Add new piece of meta. * * @param WC_Data $data Data object. * @param object $meta Meta object (containing ->key and ->value). * @return int meta ID */ public function add_meta( &$data, $meta ); /** * Update meta. * * @param WC_Data $data Data object. * @param object $meta Meta object (containing ->id, ->key and ->value). */ public function update_meta( &$data, $meta ); }