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

    Creates a user-mode logical name in the specified table.

    User-mode logical names created within the process logical
    name tables are used for the execution of a single image; for
    example, you can create a user-mode logical name to allow an
    image executing in a command procedure to redefine SYS$INPUT.
    User-mode entries are deleted from the process logical name table
    when any image executing in the process exits (that is, after
    a DCL command or user program that executes an image completes
    execution). Also, user-mode logical names are automatically
    deleted when invoking and exiting a command procedure.