Library /sys$common/syshlp/dbg$help.hlb DEBUG, SET, PROCESS, Qualifiers, /VISIBLE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Makes the specified process the visible process. This switches
    your debugging context to the specified process, so that symbol
    lookups and the setting of breakpoints, and so on, are done
    in the context of that process. When using /VISIBLE, you must
    specify one process.