Do people interpret this syntax to mean that you can only have an UNDER
clause when using the OF <user-defined type> clause as well?
<table definition> ::= CREATE [ <table scope> ] TABLE <table name> <table contents
source> [ ON COMMIT <table commit action> ROWS ]
<table contents source> ::= <table element list> | OF <user-defined type>
[ <subtable clause> ] [ <table element list> ] <subtable clause> ::= UNDER
<supertableclause>
