MGVTBL fields access

In the struct mgvtbl there're three trailing fields - svt_copy,
svt_dup, svt_local - that were added to it in the 5.8 series. Some
modules on CPAN use their own custom definitions of MGVTBL, with only
5 out 8 members, leaving those three fields out. This works because of
all accesses to them in core are guarded with appropriate MGf_ flags.
Some others check for the presence of a MGf_ definitions or for the
BCD version and define their structs correctly with all required
fields.

Are those modules that assume that all accesses to those three fields
are guarded by the corresponding MGf_ flag right? Or there's no such
promise from the core, so they have a bug lurking?

Best regards,
Sergey Aleynikov

• MGVTBL fields access by Sergey Aleynikov
• Re: MGVTBL fields access by Dave Mitchell