Presumably cpan-upstream module changes are soaked by cpan testers successfully before appearing in blead. That doesn't happen with our blead-upstream patches, and that can lead to problems. I believe we need to institute some procedures to ensure that we don't inadvertently break blead-upstream modules when run on older perls. Obviously, changing a comment or documentation accompanied by a version dump isn't likely to break things, and wouldn't need to be subject to any procedures we may institute. I'm writing this because Devel::PPPort is now broken on Perl 5.13.0 (and presumably earlier) by this recent commit: commit 7169efc77525df70484a824bff4ceebd1fafc760 *Author: Tony Cook <tony@develop-help.com> Date: Thu Jul 15 13:13:03 2021 +1000 skip using gcc brace groups for STMT_START/END This warns (and warns a lot) on clang, and since these are documented to only work to make a single statement, so there's little value to allowing them to work in an expression. An alternative would be to disable GCC brace groups on clang, but these are used extensively in DEBUGGING builds to add extra checks in sv.h. I certainly wouldn't have predicted the breakage from reading the commit code; the way it showed up was I was trying to incorporate it into the next release of D:P, and this involves testing on early perls. But this could happen to any dual life moduleThread Next