I think I now know what's happening (at least mostly). perl5db.pl uses the magic typeglob PL_DBline (aka DB::dbline) to set breakpoints. The magic for this typeglob calls Perl_magic_setdbline, which sets op_private of the COP associated with the breakpoint to 1 or 0 as appropriate. Im not sure where the value 2 comes into play, though. -- That he said that that that that is is is debatable, is debatable.