Punctuation symbols are:

      [ ]       Brackets  enclose  an  optional  portion  of   a   format.
                Brackets  around  vertically stacked entries indicate that
                you can select one of the  enclosed  elements.   You  must
                include all punctuation as it appears in the brackets.

      { }       Braces enclose a mandatory portion of  a  general  format.
                Braces around vertically stacked entries indicate that you
                must choose one of the  enclosed  elements.   Braces  also
                group  portions  of  a format as a unit.  You must include
                all punctuation as it appears in the braces.

      ...       An ellipsis indicates that you can repeat the  immediately
                preceding  language  element.   An  ellipsis  following  a
                format unit enclosed in brackets or braces means that  you
                can  repeat  the  entire  unit.   If  repeated elements or
                format units must be separated by commas, the ellipsis  is
                preceded by a comma (,...).