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

       /JSB
       /NOJSB

    (VAX only) Qualifies /INTO. Use with /INTO and one of the
    following qualifiers:

       /BRANCH
       /CALL
       /INSTRUCTION
       /INSTRUCTION=(opcode[, . . . ])
       /LINE
       /VECTOR_INSTRUCTION

    The /JSB qualifier is the default for all languages except DIBOL.
    It lets the debugger break within routines that are called by the
    JSB or CALL instruction. The /NOJSB qualifier (the DIBOL default)
    specifies that breakpoints not be set within routines called
    by JSB instructions. In DIBOL, application-declared routines
    are called by the CALL instruction and DIBOL Run-Time Library
    routines are called by the JSB instruction.