VMS Help RMS, $WAIT, Argument  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 control-block

    type:
    access:
    mechanism:    0

 fab or rab

    OpenVMS usage:fab or rab
    type:         longword (unsigned)
    access:       modify
    mechanism:    by reference

    FAB or RAB control block whose contents are to be used as
    indirect arguments for the Open service call. The fab or rab
    argument is the address of the FAB or RAB control block.