VMS Help RMS, RMS Control Block Macros, $XABRDT  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    The $XABRDT macro allocates and initializes a XABRDT. No value is
    returned for this assembly-time operation.

    Format

      $XABRDT  NXT=next-xab-address