/sys$common/syshlp/helplib.hlb Lexicals, F$STRING, Argument  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 expression

    The integer or string expression to be evaluated.

    If you specify an integer expression, the F$STRING function
    evaluates the expression, converts the resulting integer to
    a string, and returns the result. If you specify a string
    expression, the F$STRING function evaluates the expression and
    returns the result.

    When converting an integer to a string, the F$STRING function
    uses decimal representation and omits leading zeros. When
    converting a negative integer, the F$STRING function places a
    minus sign at the beginning string representation of the integer.