The Invoke $FAO System Service to Format Output routine calls
    the $FAO system service, returning a string in the semantics
    you provide. If called with other than a fixed-length string
    for output, the length of the resultant string is limited to 256
    bytes and truncation occurs.

    Format

      LIB$SYS_FAO  character-string, [resultant-length]

                   ,resultant-string [,directive-argument

                   ,...]

1  –  Returns

    OpenVMS usage:cond_value
    type:         longword (unsigned)
    access:       write only
    mechanism:    by value

2  –  Arguments

 character-string

    OpenVMS usage:char_string
    type:         character string
    access:       read only
    mechanism:    by descriptor

    ASCII control string, consisting of the fixed text of the output
    string and FAO directives. The character-string argument contains
    the address of a descriptor pointing to this control string.

 resultant-length

    OpenVMS usage:word_unsigned
    type:         word (unsigned)
    access:       write only
    mechanism:    by reference

    Length of the output string. The resultant-length argument
    contains the address of an unsigned word integer that is this
    length.

 resultant-string

    OpenVMS usage:char_string
    type:         character string
    access:       write only
    mechanism:    by descriptor

    Fully formatted output string returned by LIB$SYS_FAO. The
    resultant-string argument contains the address of a descriptor
    pointing to this output string.

 directive-argument

    OpenVMS usage:varying_arg
    type:         unspecified
    access:       read only
    mechanism:    unspecified

    Directive argument contained in longwords. Depending on the
    directive, a directive-argument argument can be a value to
    be converted, the address of the string to be inserted, or a
    length or argument count. The passing mechanism for each of these
    arguments should be the one expected by the $FAO system service.