x

    A character, such as a left parenthesis or bracket, that you can
    specify to precede the number or letter. You must enclose the
    character in quotation marks (" ") or apostrophes (' ').

 y

    One of the following one- or two-letter codes:

    Code  Form of Sequence and Case

    D     Decimal numbers
    O     Octal numbers
    H     Hexadecimal numbers
    RU    Roman uppercase numerals
    RL    Roman lowercase numerals
    RM    Roman mixed case numerals - only first numeral is uppercase
    LU    Letters, uppercase
    LL    Letters, lowercase
    LM    Letters, mixed case - only first letter is uppercase

 z

    A character, such as a right parenthesis or bracket, that you
    can specify to follow the number or letter. You must enclose the
    character in quotation marks (" ") or apostrophes (' ').