UUID(size) should be disallowed

It is possible to specify a length for a UUID column:

MariaDB [test]> CREATE TABLE t (

    ->     uuid UUID(24)

    -> );

Query OK, 0 rows affected (0.040 sec)

As far as I can tell, this has no effect, so it shouldn't be allowed or it should at least produce a warning. But if it has an effect, it should be documented.