{ ROWS | RANGE }
{ BETWEEN
  { UNBOUNDED PRECEDING
  | CURRENT ROW
  | value_expr { PRECEDING | FOLLOWING }
  } 
  AND
  { UNBOUNDED FOLLOWING
  | CURRENT ROW
  | value_expr { PRECEDING | FOLLOWING }
  }
| { UNBOUNDED PRECEDING
  | CURRENT ROW
  | value_expr PRECEDING
  }
}

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