VMS Help MACRO, /MIGRATION, Macros for 64-Bit Addressing, $IS DESC64, Parameters  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 desc_addr

    The address of the descriptor to test.

 target

    The label to branch to if the descriptor is in 64-bit format.

  size=long

    The size of the address pointing to the descriptor. Acceptable
    values are "long" (the default) and "quad".