VMS Help MACRO, /MIGRATION, Parameters  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 filespec[+...]

    Specifies a VAX MACRO assembly language source file to be
    compiled. If you specify more than one file, separate the
    file specifications with plus signs (+).  File specifications
    separated by plus signs are concatenated into one input file and
    produce a single object file and, if indicated, a listing file.

                                   NOTE

       Unlike the VAX assembler, the MACRO-32 compiler does not
       support the creation of separate object files when the
       source files are separated by a comma (,).

    You cannot include a wildcard character in a file specification.
    For each file specification, the compiler command supplies a
    default file type of MAR.

    The compiler creates output files of one version higher than the
    highest version existing in the target directory.