Library /sys$common/syshlp/sysmanhelp.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 a spawned subprocess
    to which control passes. The process must already exist, be part
    of your current job tree, 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.