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

                   ,...]