VMS Help MACRO, VAX MACRO Assembler, Operand Formats, Autoincrement deferred  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    The register contains an address that is the address of  the
    operand address  (a  pointer  to  the operand).  After evaluating
    the operand address, the processor increments the contents of the
    register  by  4 (the  size  in bytes of an address).  Autoincrement
    deferred mode can be used with index mode.

       @(Rn)+
       @(AP)+
       @(FP)+
       @(SP)+

    n

    A number in the range of 0 through 12