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

       /EVENT=event-name

    Causes the debugger to break on the specified event (if that
    event is defined and detected by the current event facility).
    If you specify an address expression with /EVENT, causes the
    debugger to break whenever the specified event occurs for that
    address expression. You cannot specify an address expression with
    certain event names.

    Event facilities are available for programs that call Ada or SCAN
    routines or that use POSIX Threads services. Use the SHOW EVENT_
    FACILITY command to identify the current event facility and the
    associated event names.