[ [[NOT] DEFERRABLE] [INITIALLY { IMMEDIATE | DEFERRED }]
| [INITIALLY { IMMEDIATE | DEFERRED }] [[NOT] DEFERRABLE]
]
[ RELY | NORELY ] [using_index_clause] [ ENABLE | DISABLE ] 
[ VALIDATE | NOVALIDATE ] [exceptions_clause]

For information on the symbols and conventions of Backus-Naur Form (BNF) syntax, see Appendix A.