Perl core

       This document is the master document which records all written policies
       about how the Perl 5 Porters collectively develop and maintain the Perl

   Perl 5 Porters
       Subscribers to perl5-porters (the porters themselves) come in several
       flavours.  Some are quiet curious lurkers, who rarely pitch in and
       instead watch the ongoing development to ensure they're forewarned of
       new changes or features in Perl.  Some are representatives of vendors,
       who are there to make sure that Perl continues to compile and work on
       their platforms.  Some patch any reported bug that they know how to
       fix, some are actively patching their pet area (threads, Win32, the
       regexp -engine), while others seem to do nothing but complain.  In
       other words, it's your usual mix of technical people.

       Over this group of porters presides Larry Wall.  He has the final word
       in what does and does not change in any of the Perl programming
       languages.  These days, Larry spends most of his time on Perl 6, while
       Perl 5 is shepherded by a "pumpking", a porter responsible for deciding
       what goes into each release and ensuring that releases happen on a
       regular basis.

       Larry sees Perl development along the lines of the US government:
       there's the Legislature (the porters), the Executive branch (the
       -pumpking), and the Supreme Court (Larry).  The legislature can discuss
       and submit patches to the executive branch all they like, but the
       executive branch is free to veto them.  Rarely, the Supreme Court will
       side with the executive branch over the legislature, or the legislature
       over the executive branch.  Mostly, however, the legislature and the
       executive branch are supposed to get along and work out their
       differences without impeachment or court cases.

       You might sometimes see reference to Rule 1 and Rule 2.  Larry's power
       as Supreme Court is expressed in The Rules:

       1.  Larry is always by definition right about how Perl should behave.
           This means he has final veto power on the core functionality.

       2.  Larry is allowed to change his mind about any matter at a later
           date, regardless of whether he previously invoked Rule 1.

       Got that?  Larry is always right, even when he was wrong.  It's rare to
       see either Rule exercised, but they are often alluded to.

       Perl 5 is developed by a community, not a corporate entity. Every
       change contributed to the Perl core is the result of a donation.
       Typically, these donations are contributions of code or time by
       individual members of our community. On occasion, these donations come
       in the form of corporate or organizational sponsorship of a particular

       o   We "officially" support the two most recent stable release series.
           5.12.x and earlier are now out of support.  As of the release of
           5.18.0, we will "officially" end support for Perl 5.14.x, other
           than providing security updates as described below.

       o   To the best of our ability, we will attempt to fix critical issues
           in the two most recent stable 5.x release series.  Fixes for the
           current release series take precedence over fixes for the previous
           release series.

       o   To the best of our ability, we will provide "critical" security
           patches / releases for any major version of Perl whose 5.x.0
           release was within the past three years.  We can only commit to
           providing these for the most recent .y release in any 5.x.y series.

       o   We will not provide security updates or bug fixes for development
           releases of Perl.

       o   We encourage vendors to ship the most recent supported release of
           Perl at the time of their code freeze.

       o   As a vendor, you may have a requirement to backport security fixes
           beyond our 3 year support commitment.  We can provide limited
           support and advice to you as you do so and, where possible will try
           to apply those patches to the relevant -maint branches in git,
           though we may or may not choose to make numbered releases or
           "official" patches available.  Contact us at
           <> to begin that process.

       Our community has a long-held belief that backward-compatibility is a
       virtue, even when the functionality in question is a design flaw.

       We would all love to unmake some mistakes we've made over the past
       decades.  Living with every design error we've ever made can lead to
       painful stagnation.  Unwinding our mistakes is very, very difficult.
       Doing so without actively harming our users is nearly impossible.

       Lately, ignoring or actively opposing compatibility with earlier
       versions of Perl has come into vogue.  Sometimes, a change is proposed
       which wants to usurp syntax which previously had another meaning.
       Sometimes, a change wants to improve previously-crazy semantics.

       Down this road lies madness.

       Requiring end-user programmers to change just a few language
       constructs, even language constructs which no well-educated developer
       would ever intentionally use is tantamount to saying "you should not
       upgrade to a new release of Perl unless you have 100% test coverage and
       can do a full manual audit of your codebase."  If we were to have tools
       capable of reliably upgrading Perl source code from one version of Perl
       to another, this concern could be significantly mitigated.

       disabled.  Which backward-incompatible changes are controlled
       implicitly by a 'use v5.x.y' is a decision which should be made by the
       pumpking in consultation with the community.

       When a backward-incompatible change can't be toggled lexically, the
       decision to change the language must be considered very, very
       carefully.  If it's possible to move the old syntax or semantics out of
       the core language and into XS-land, that XS module should be enabled by
       default unless the user declares that they want a newer revision of

       Historically, we've held ourselves to a far higher standard than
       backward-compatibility -- bugward-compatibility.  Any accident of
       implementation or unintentional side-effect of running some bit of code
       has been considered to be a feature of the language to be defended with
       the same zeal as any other feature or functionality.  No matter how
       frustrating these unintentional features may be to us as we continue to
       improve Perl, these unintentional features often deserve our
       protection.  It is very important that existing software written in
       Perl continue to work correctly.  If end-user developers have adopted a
       bug as a feature, we need to treat it as such.

       New syntax and semantics which don't break existing language constructs
       and syntax have a much lower bar.  They merely need to prove themselves
       to be useful, elegant, well designed, and well tested.

       To make sure we're talking about the same thing when we discuss the
       removal of features or functionality from the Perl core, we have
       specific definitions for a few words and phrases.

           If something in the Perl core is marked as experimental, we may
           change its behaviour, deprecate or remove it without notice. While
           we'll always do our best to smooth the transition path for users of
           experimental features, you should contact the perl5-porters
           mailinglist if you find an experimental feature useful and want to
           help shape its future.

           If something in the Perl core is marked as deprecated, we may
           remove it from the core in the next stable release series, though
           we may not. As of Perl 5.12, deprecated features and modules warn
           the user as they're used.  When a module is deprecated, it will
           also be made available on CPAN.  Installing it from CPAN will
           silence deprecation warnings for that module.

           If you use a deprecated feature or module and believe that its
           removal from the Perl core would be a mistake, please contact the
           perl5-porters mailinglist and plead your case.  We don't deprecate
           things without a good reason, but sometimes there's a
           counterargument we haven't considered.  Historically, we did not
           distinguish between "deprecated" and "discouraged" features.

           is removed, it will no longer ship with Perl, but will continue to
           be available on CPAN.

       o   New releases of maint should contain as few changes as possible.
           If there is any question about whether a given patch might merit
           inclusion in a maint release, then it almost certainly should not
           be included.

       o   Portability fixes, such as changes to Configure and the files in
           hints/ are acceptable. Ports of Perl to a new platform,
           architecture or OS release that involve changes to the
           implementation are NOT acceptable.

       o   Acceptable documentation updates are those that correct factual
           errors, explain significant bugs or deficiencies in the current
           implementation, or fix broken markup.

       o   Patches that add new warnings or errors or deprecate features are
           not acceptable.

       o   Patches that fix crashing bugs that do not otherwise change Perl's
           functionality or negatively impact performance are acceptable.

       o   Patches that fix CVEs or security issues are acceptable, but should
           be run through the mailing list
           rather than applied directly.

       o   Patches that fix regressions in perl's behavior relative to
           previous releases are acceptable.

       o   Updates to dual-life modules should consist of minimal patches to
           fix crashing or security issues (as above).

       o   Minimal patches that fix platform-specific test failures or
           installation issues are acceptable. When these changes are made to
           dual-life modules for which CPAN is canonical, any changes should
           be coordinated with the upstream author.

       o   New versions of dual-life modules should NOT be imported into
           maint.  Those belong in the next stable series.

       o   Patches that add or remove features are not acceptable.

       o   Patches that break binary compatibility are not acceptable.
           (Please talk to a pumpking.)

   Getting changes into a maint branch
       Historically, only the pumpking cherry-picked changes from bleadperl
       into maintperl.  This has scaling problems.  At the same time,
       maintenance branches of stable versions of Perl need to be treated with
       great care. To that end, as of Perl 5.12, we have a new process for
       maint branches.

       should have control over their work, and that it is a responsibility of
       the rest of the Perl community to ensure that they retain this control.
       It is an attempt to document the standards to which we, as Perl
       developers, intend to hold ourselves.  It is an attempt to write down
       rough guidelines about the respect we owe each other as Perl

       This statement is not a legal contract.  This statement is not a legal
       document in any way, shape, or form.  Perl is distributed under the GNU
       Public License and under the Artistic License; those are the precise
       legal terms.  This statement isn't about the law or licenses.  It's
       about community, mutual respect, trust, and good-faith cooperation.

       We recognize that the Perl core, defined as the software distributed
       with the heart of Perl itself, is a joint project on the part of all of
       us.  From time to time, a script, module, or set of modules (hereafter
       referred to simply as a "module") will prove so widely useful and/or so
       integral to the correct functioning of Perl itself that it should be
       distributed with the Perl core.  This should never be done without the
       author's explicit consent, and a clear recognition on all parts that
       this means the module is being distributed under the same terms as Perl
       itself.  A module author should realize that inclusion of a module into
       the Perl core will necessarily mean some loss of control over it, since
       changes may occasionally have to be made on short notice or for
       consistency with the rest of Perl.

       Once a module has been included in the Perl core, however, everyone
       involved in maintaining Perl should be aware that the module is still
       the property of the original author unless the original author
       explicitly gives up their ownership of it.  In particular:

       o   The version of the module in the Perl core should still be
           considered the work of the original author.  All patches, bug
           reports, and so forth should be fed back to them.  Their
           development directions should be respected whenever possible.

       o   Patches may be applied by the pumpkin holder without the explicit
           cooperation of the module author if and only if they are very
           minor, time-critical in some fashion (such as urgent security
           fixes), or if the module author cannot be reached.  Those patches
           must still be given back to the author when possible, and if the
           author decides on an alternate fix in their version, that fix
           should be strongly preferred unless there is a serious problem with
           it.  Any changes not endorsed by the author should be marked as
           such, and the contributor of the change acknowledged.

       o   The version of the module distributed with Perl should, whenever
           possible, be the latest version of the module as distributed by the
           author (the latest non-beta version in the case of public Perl
           releases), although the pumpkin holder may hold off on upgrading
           the version of the module distributed with Perl to the latest
           version until the latest version has had sufficient testing.

       In other words, the author of a module should be considered to have
       Larry.  If this is done, it must then be made explicit in the module as
       distributed with the Perl core that it is a forked version and that
       while it is based on the original author's work, it is no longer
       maintained by them.  This must be noted in both the documentation and
       in the comments in the source of the module.

       Again, this should be a last resort only.  Ideally, this should never
       happen, and every possible effort at cooperation and compromise should
       be made before doing this.  If it does prove necessary to fork a module
       for the overall health of Perl, proper credit must be given to the
       original author in perpetuity and the decision should be constantly re-
       evaluated to see if a remerging of the two branches is possible down
       the road.

       In all dealings with contributed modules, everyone maintaining Perl
       should keep in mind that the code belongs to the original author, that
       they may not be on perl5-porters at any given time, and that a patch is
       not official unless it has been integrated into the author's copy of
       the module.  To aid with this, and with points #1, #2, and #3 above,
       contact information for the authors of all contributed modules should
       be kept with the Perl distribution.

       Finally, the Perl community as a whole recognizes that respect for
       ownership of code, respect for artistic control, proper credit, and
       active effort to prevent unintentional code skew or communication gaps
       is vital to the health of the community and Perl itself.  Members of a
       community should not normally have to resort to rules and laws to deal
       with each other, and this document, although it contains rules so as to
       be clear, is about an attitude and general approach.  The first step in
       any dispute should be open communication, respect for opposing views,
       and an attempt at a compromise.  In nearly every circumstance nothing
       more will be necessary, and certainly no more drastic measure should be
       used until every avenue of communication and discussion has failed.

       Perl's documentation is an important resource for our users. It's
       incredibly important for Perl's documentation to be reasonably coherent
       and to accurately reflect the current implementation.

       Just as P5P collectively maintains the codebase, we collectively
       maintain the documentation.  Writing a particular bit of documentation
       doesn't give an author control of the future of that documentation.  At
       the same time, just as source code changes should match the style of
       their surrounding blocks, so should documentation changes.

       Examples in documentation should be illustrative of the concept they're
       explaining.  Sometimes, the best way to show how a language feature
       works is with a small program the reader can run without modification.
       More often, examples will consist of a snippet of code containing only
       the "important" bits.  The definition of "important" varies from
       snippet to snippet.  Sometimes it's important to declare "use strict"
       and "use warnings", initialize all variables and fully catch every
       error condition.  More often than not, though, those things obscure the
       lesson the example was intended to teach.
       doesn't need to fully describe how all old versions used to work.

       "Social Contract about Contributed Modules" originally by Russ Allbery
       <> and the perl5-porters.

perl v5.18.2                      2013-11-04                     PERLPOLICY(1)
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