get_registered_meta_keys example

function registered_meta_key_exists( $object_type, $meta_key, $object_subtype = '' ) {
    $meta_keys = get_registered_meta_keys( $object_type, $object_subtype );

    return isset( $meta_keys[ $meta_key ] );
}

/** * Unregisters a meta key from the list of registered keys. * * @since 4.6.0 * @since 4.9.8 The `$object_subtype` parameter was added. * * @param string $object_type Type of object metadata is for. Accepts 'post', 'comment', 'term', 'user', * or any other object type with an associated meta table. * @param string $meta_key Metadata key. * @param string $object_subtype Optional. The subtype of the object type. Default empty string. * @return bool True if successful. False if the meta key was not registered. */

    protected function get_registered_fields() {
        $registered = array();

        $meta_type    = $this->get_meta_type();
        $meta_subtype = $this->get_meta_subtype();

        $meta_keys = get_registered_meta_keys( $meta_type );
        if ( ! empty( $meta_subtype ) ) {
            $meta_keys = array_merge( $meta_keys, get_registered_meta_keys( $meta_type, $meta_subtype ) );
        }

        foreach ( $meta_keys as $name => $args ) {
            if ( empty( $args['show_in_rest'] ) ) {
                continue;
            }

            $rest_args = array();