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On 12 May 2016 at 11:59, Jonathan Goble <> wrote:
> On Fri, May 6, 2016 at 11:46 AM, Roberto Ierusalimschy
> <> wrote:
>> - new semantics for empty matches ("Python rule")
> After thinking about it for a few days, I'm going to argue that this
> change flat-out does not belong in a bugfix release. It's not a bugfix
> at all; it's a change in the behavior of a feature that, although it
> is undocumented, is reasonably well-known enough that a
> non-insignificant number of people and libraries may be reliant upon
> the existing behavior, and is thus a backwards-incompatible change.
> The very fact that someone needed to start a thread a few days ago
> asking how to programmatically distinguish between 5.3.2 and the
> proposed 5.3.3 is indicative of the fact that this will break people's
> code, violating the trust that people have regarding bugfix releases
> being backwards compatible.
> Therefore, as a backwards-incompatible change, this feature should be
> removed from the 5.3.3 release candidate and should be delayed until
> 5.4 or 6.0 (whichever the next version ends up being).
> Thoughts on this?

Previously the behaviour was undefined.
Changes in undefined behaviour are allowed between implementations as
well as between bugfix releases.