public function save_field_post2post( $post_id, $field, $old, $new ) {
		delete_post_meta( $post_id, $field['meta'] );
		$new = (array) $new;
		$new = array_unique( $new );
		foreach ( $new as $id ) {
			add_post_meta( $post_id, $field['meta'], $id );
		}
	}