enable_spec

enable_spec 
      ::= 
      ( ( ( "unique" "(" column_list ")" ) 
      | ( "primary" "key" ) 
      | ( "constraint" constraint_name ) ) 
      [ "using" "index" index_storage { index_storage } ] 
      [ "exceptions" "into" [ schema_name "." ] table_name ] ) 
      | ( "all" "triggers" ) 

This rule is called by

alter_table_spec
create_table