Library /sys$common/syshlp/dbg$help.hlb DEBUG, Built in Symbols, %LABEL  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    %LABEL n is the debugger syntax for referring to label n in your
    program. This is intended for languages like FORTRAN which have
    numeric program labels. You can qualify the label with a path
    name specifying the containing module.

    Example:

    DBG> SET BREAK MODULENAME\%LABEL 10

    The old syntax of %LABEL MODULENAME\n is no longer accepted.