COMMENT ON 
{ TABLE [schema .] { table | view | materialized view }
| COLUMN [schema .] { table . | view . | materialized view . } column 
| OPERATOR [schema .] operator
| INDEXTYPE [schema .] indextype
}
IS 'text';

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