/sys$common/syshlp/helplib.hlb ATTACH, Parameter  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 process-name

    Specifies the name of a parent process or spawned subprocess to
    which control passes. The process must already exist, be part of
    your current job, and share the same input stream as your current
    process. However, the process cannot be your current process or a
    subprocess created with the /NOWAIT qualifier.

    Process names can contain from 1 to 15 alphanumeric characters.
    If a connection to the specified process cannot be made, an error
    message is displayed.

    The process-name parameter is incompatible with the
    /IDENTIFICATION qualifier.