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perlpolicy: clarify what "feature can be replaced" means
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1=encoding utf8
2
48cb5b3a 3=head1 NAME
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9a7064ee 5perlpolicy - Various and sundry policies and commitments related to the Perl core
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6
7=head1 DESCRIPTION
8
9This document is the master document which records all written
10policies about how the Perl 5 Porters collectively develop and maintain
11the Perl core.
12
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13=head1 GOVERNANCE
14
15=head2 Perl 5 Porters
16
17Subscribers to perl5-porters (the porters themselves) come in several flavours.
18Some are quiet curious lurkers, who rarely pitch in and instead watch
19the ongoing development to ensure they're forewarned of new changes or
20features in Perl. Some are representatives of vendors, who are there
21to make sure that Perl continues to compile and work on their
22platforms. Some patch any reported bug that they know how to fix,
23some are actively patching their pet area (threads, Win32, the regexp
24-engine), while others seem to do nothing but complain. In other
25words, it's your usual mix of technical people.
26
27Over this group of porters presides Larry Wall. He has the final word
28in what does and does not change in any of the Perl programming languages.
29These days, Larry spends most of his time on Perl 6, while Perl 5 is
30shepherded by a "pumpking", a porter responsible for deciding what
31goes into each release and ensuring that releases happen on a regular
32basis.
33
34Larry sees Perl development along the lines of the US government:
35there's the Legislature (the porters), the Executive branch (the
36-pumpking), and the Supreme Court (Larry). The legislature can
37discuss and submit patches to the executive branch all they like, but
38the executive branch is free to veto them. Rarely, the Supreme Court
39will side with the executive branch over the legislature, or the
40legislature over the executive branch. Mostly, however, the
41legislature and the executive branch are supposed to get along and
42work out their differences without impeachment or court cases.
43
44You might sometimes see reference to Rule 1 and Rule 2. Larry's power
45as Supreme Court is expressed in The Rules:
46
47=over 4
48
49=item 1
50
51Larry is always by definition right about how Perl should behave.
52This means he has final veto power on the core functionality.
53
54=item 2
55
56Larry is allowed to change his mind about any matter at a later date,
57regardless of whether he previously invoked Rule 1.
58
59=back
60
61Got that? Larry is always right, even when he was wrong. It's rare
62to see either Rule exercised, but they are often alluded to.
63
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64=head1 MAINTENANCE AND SUPPORT
65
66Perl 5 is developed by a community, not a corporate entity. Every change
67contributed to the Perl core is the result of a donation. Typically, these
68donations are contributions of code or time by individual members of our
69community. On occasion, these donations come in the form of corporate
70or organizational sponsorship of a particular individual or project.
71
72As a volunteer organization, the commitments we make are heavily dependent
73on the goodwill and hard work of individuals who have no obligation to
74contribute to Perl.
75
3b4ebcde 76That being said, we value Perl's stability and security and have long
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77had an unwritten covenant with the broader Perl community to support
78and maintain releases of Perl.
79
80This document codifies the support and maintenance commitments that
81the Perl community should expect from Perl's developers:
82
83=over
84
85=item *
86
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87We "officially" support the two most recent stable release series. 5.14.x
88and earlier are now out of support. As of the release of 5.20.0, we will
89"officially" end support for Perl 5.16.x, other than providing security
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90updates as described below.
91
92=item *
93
94To the best of our ability, we will attempt to fix critical issues
e26b5c49 95in the two most recent stable 5.x release series. Fixes for the
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96current release series take precedence over fixes for the previous
97release series.
98
99=item *
100
101To the best of our ability, we will provide "critical" security patches
f50f542d 102/ releases for any major version of Perl whose 5.x.0 release was within
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103the past three years. We can only commit to providing these for the
104most recent .y release in any 5.x.y series.
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105
106=item *
107
108We will not provide security updates or bug fixes for development
109releases of Perl.
110
111=item *
112
113We encourage vendors to ship the most recent supported release of
114Perl at the time of their code freeze.
115
116=item *
117
118As a vendor, you may have a requirement to backport security fixes
119beyond our 3 year support commitment. We can provide limited support and
120advice to you as you do so and, where possible will try to apply
121those patches to the relevant -maint branches in git, though we may or
122may not choose to make numbered releases or "official" patches
123available. Contact us at E<lt>perl5-security-report@perl.orgE<gt>
124to begin that process.
125
126=back
127
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128=head1 BACKWARD COMPATIBILITY AND DEPRECATION
129
130Our community has a long-held belief that backward-compatibility is a
131virtue, even when the functionality in question is a design flaw.
132
133We would all love to unmake some mistakes we've made over the past
134decades. Living with every design error we've ever made can lead
135to painful stagnation. Unwinding our mistakes is very, very
136difficult. Doing so without actively harming our users is
137nearly impossible.
138
139Lately, ignoring or actively opposing compatibility with earlier versions
140of Perl has come into vogue. Sometimes, a change is proposed which
141wants to usurp syntax which previously had another meaning. Sometimes,
339a461d 142a change wants to improve previously-crazy semantics.
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143
144Down this road lies madness.
145
146Requiring end-user programmers to change just a few language constructs,
147even language constructs which no well-educated developer would ever
148intentionally use is tantamount to saying "you should not upgrade to
149a new release of Perl unless you have 100% test coverage and can do a
150full manual audit of your codebase." If we were to have tools capable of
151reliably upgrading Perl source code from one version of Perl to another,
152this concern could be significantly mitigated.
153
154We want to ensure that Perl continues to grow and flourish in the coming
155years and decades, but not at the expense of our user community.
156
157Existing syntax and semantics should only be marked for destruction in
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158very limited circumstances. If they believed to be very rarely used,
159stand in the way of actual improvement to the Perl language or perl
160interpreter, and if affected code can be easily updated to continue
161working, they may be considered for removal. When in doubt, caution
162dictates that we will favor backward compatibility. When a feature is
163deprecated, a statement of reasoning describing the decision process
164will be posted, and a link to it will be provided in the relevant
165perldelta documents.
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166
167Using a lexical pragma to enable or disable legacy behavior should be
168considered when appropriate, and in the absence of any pragma legacy
169behavior should be enabled. Which backward-incompatible changes are
170controlled implicitly by a 'use v5.x.y' is a decision which should be
171made by the pumpking in consultation with the community.
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172
173Historically, we've held ourselves to a far higher standard than
174backward-compatibility -- bugward-compatibility. Any accident of
175implementation or unintentional side-effect of running some bit of code
176has been considered to be a feature of the language to be defended with
177the same zeal as any other feature or functionality. No matter how
178frustrating these unintentional features may be to us as we continue
179to improve Perl, these unintentional features often deserve our
180protection. It is very important that existing software written in
181Perl continue to work correctly. If end-user developers have adopted a
182bug as a feature, we need to treat it as such.
183
184New syntax and semantics which don't break existing language constructs
185and syntax have a much lower bar. They merely need to prove themselves
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186to be useful, elegant, well designed, and well tested. In most cases,
187these additions will be marked as I<experimental> for some time. See
188below for more on that.
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189
190=head2 Terminology
191
192To make sure we're talking about the same thing when we discuss the removal
193of features or functionality from the Perl core, we have specific definitions
194for a few words and phrases.
195
196=over
197
198=item experimental
199
200If something in the Perl core is marked as B<experimental>, we may change
201its behaviour, deprecate or remove it without notice. While we'll always
202do our best to smooth the transition path for users of experimental
203features, you should contact the perl5-porters mailinglist if you find
204an experimental feature useful and want to help shape its future.
205
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206Experimental features must be experimental in two stable releases before being
207marked non-experimental. Experimental features will only have their
208experimental status revoked when they no longer have any design-changing bugs
209open against them and when they have remained unchanged in behavior for the
210entire length of a development cycle. In other words, a feature present in
211v5.20.0 may be marked no longer experimental in v5.22.0 if and only if its
212behavior is unchanged throughout all of v5.21.
213
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214=item deprecated
215
216If something in the Perl core is marked as B<deprecated>, we may remove it
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217from the core in the future, though we might not. Generally, backward
218incompatible changes will have deprecation warnings for two release
219cycles before being removed, but may be removed after just one cycle if
220the risk seems quite low or the benefits quite high.
221
222As of
70e4a83b 223Perl 5.12, deprecated features and modules warn the user as they're used.
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224When a module is deprecated, it will also be made available on CPAN.
225Installing it from CPAN will silence deprecation warnings for that module.
226
227If you use a deprecated feature or module and believe that its removal from
228the Perl core would be a mistake, please contact the perl5-porters
229mailinglist and plead your case. We don't deprecate things without a good
230reason, but sometimes there's a counterargument we haven't considered.
231Historically, we did not distinguish between "deprecated" and "discouraged"
232features.
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233
234=item discouraged
235
236From time to time, we may mark language constructs and features which we
237consider to have been mistakes as B<discouraged>. Discouraged features
5c5fd8eb 238aren't currently candidates for removal, but
70e4a83b 239we may later deprecate them if they're found to stand in the way of a
9a7064ee 240significant improvement to the Perl core.
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241
242=item removed
243
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244Once a feature, construct or module has been marked as deprecated, we
245may remove it from the Perl core. Unsurprisingly,
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246we say we've B<removed> these things. When a module is removed, it will
247no longer ship with Perl, but will continue to be available on CPAN.
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248
249=back
48cb5b3a 250
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251=head1 MAINTENANCE BRANCHES
252
253=over
254
255=item *
256
257New releases of maint should contain as few changes as possible.
258If there is any question about whether a given patch might merit
259inclusion in a maint release, then it almost certainly should not
260be included.
261
262=item *
263
264Portability fixes, such as changes to Configure and the files in
265hints/ are acceptable. Ports of Perl to a new platform, architecture
266or OS release that involve changes to the implementation are NOT
267acceptable.
268
269=item *
270
b6538e4f 271Acceptable documentation updates are those that correct factual errors,
17c80487 272explain significant bugs or deficiencies in the current implementation,
b6538e4f 273or fix broken markup.
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274
275=item *
276
277Patches that add new warnings or errors or deprecate features
278are not acceptable.
279
280=item *
281
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282Patches that fix crashing bugs, assertion failures and
283memory corruption that do not otherwise change Perl's
17c80487 284functionality or negatively impact performance are acceptable.
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285
286=item *
287
288Patches that fix CVEs or security issues are acceptable, but should
289be run through the perl5-security-report@perl.org mailing list
290rather than applied directly.
291
292=item *
293
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294Patches that fix regressions in perl's behavior relative to previous
295releases are acceptable.
296
297=item *
298
17c80487 299Updates to dual-life modules should consist of minimal patches to
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300fix crashing or security issues (as above).
301
302=item *
303
bd21af11 304Minimal patches that fix platform-specific test failures or build or
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305installation issues are acceptable. When these changes are made
306to dual-life modules for which CPAN is canonical, any changes
307should be coordinated with the upstream author.
308
309=item *
310
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311New versions of dual-life modules should NOT be imported into maint.
312Those belong in the next stable series.
313
314=item *
315
316Patches that add or remove features are not acceptable.
317
318=item *
319
320Patches that break binary compatibility are not acceptable. (Please
321talk to a pumpking.)
322
323=back
324
325
326=head2 Getting changes into a maint branch
327
328Historically, only the pumpking cherry-picked changes from bleadperl
e566981e 329into maintperl. This has scaling problems. At the same time,
fcf56c88 330maintenance branches of stable versions of Perl need to be treated with
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331great care. To that end, as of Perl 5.12, we have a new process for
332maint branches.
fcf56c88 333
e566981e 334Any committer may cherry-pick any commit from blead to a maint branch if
fcf56c88 335they send mail to perl5-porters announcing their intent to cherry-pick
17c80487 336a specific commit along with a rationale for doing so and at least two
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337other committers respond to the list giving their assent. (This policy
338applies to current and former pumpkings, as well as other committers.)
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339
340=head1 CONTRIBUTED MODULES
341
342
343=head2 A Social Contract about Artistic Control
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344
345What follows is a statement about artistic control, defined as the ability
346of authors of packages to guide the future of their code and maintain
347control over their work. It is a recognition that authors should have
348control over their work, and that it is a responsibility of the rest of
349the Perl community to ensure that they retain this control. It is an
350attempt to document the standards to which we, as Perl developers, intend
351to hold ourselves. It is an attempt to write down rough guidelines about
352the respect we owe each other as Perl developers.
353
354This statement is not a legal contract. This statement is not a legal
355document in any way, shape, or form. Perl is distributed under the GNU
356Public License and under the Artistic License; those are the precise legal
357terms. This statement isn't about the law or licenses. It's about
358community, mutual respect, trust, and good-faith cooperation.
359
360We recognize that the Perl core, defined as the software distributed with
361the heart of Perl itself, is a joint project on the part of all of us.
aaa2bbb1 362From time to time, a script, module, or set of modules (hereafter referred
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363to simply as a "module") will prove so widely useful and/or so integral to
364the correct functioning of Perl itself that it should be distributed with
9a7064ee 365the Perl core. This should never be done without the author's explicit
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366consent, and a clear recognition on all parts that this means the module
367is being distributed under the same terms as Perl itself. A module author
368should realize that inclusion of a module into the Perl core will
369necessarily mean some loss of control over it, since changes may
370occasionally have to be made on short notice or for consistency with the
371rest of Perl.
372
373Once a module has been included in the Perl core, however, everyone
374involved in maintaining Perl should be aware that the module is still the
375property of the original author unless the original author explicitly
376gives up their ownership of it. In particular:
377
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378=over
379
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380=item *
381
9a7064ee 382The version of the module in the Perl core should still be considered the
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383work of the original author. All patches, bug reports, and so
384forth should be fed back to them. Their development directions
385should be respected whenever possible.
6ee623d5 386
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387=item *
388
389Patches may be applied by the pumpkin holder without the explicit
390cooperation of the module author if and only if they are very minor,
391time-critical in some fashion (such as urgent security fixes), or if
392the module author cannot be reached. Those patches must still be
393given back to the author when possible, and if the author decides on
394an alternate fix in their version, that fix should be strongly
395preferred unless there is a serious problem with it. Any changes not
396endorsed by the author should be marked as such, and the contributor
397of the change acknowledged.
398
399=item *
400
401The version of the module distributed with Perl should, whenever
402possible, be the latest version of the module as distributed by the
403author (the latest non-beta version in the case of public Perl
404releases), although the pumpkin holder may hold off on upgrading the
405version of the module distributed with Perl to the latest version
406until the latest version has had sufficient testing.
407
408=back
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409
410In other words, the author of a module should be considered to have final
411say on modifications to their module whenever possible (bearing in mind
412that it's expected that everyone involved will work together and arrive at
413reasonable compromises when there are disagreements).
414
415As a last resort, however:
416
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417
418If the author's vision of the future of their module is sufficiently
419different from the vision of the pumpkin holder and perl5-porters as a
420whole so as to cause serious problems for Perl, the pumpkin holder may
9a7064ee 421choose to formally fork the version of the module in the Perl core from the
48cb5b3a 422one maintained by the author. This should not be done lightly and
c4f5d98d 423should B<always> if at all possible be done only after direct input
48cb5b3a 424from Larry. If this is done, it must then be made explicit in the
9a7064ee 425module as distributed with the Perl core that it is a forked version and
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426that while it is based on the original author's work, it is no longer
427maintained by them. This must be noted in both the documentation and
428in the comments in the source of the module.
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429
430Again, this should be a last resort only. Ideally, this should never
431happen, and every possible effort at cooperation and compromise should be
432made before doing this. If it does prove necessary to fork a module for
433the overall health of Perl, proper credit must be given to the original
434author in perpetuity and the decision should be constantly re-evaluated to
435see if a remerging of the two branches is possible down the road.
436
437In all dealings with contributed modules, everyone maintaining Perl should
438keep in mind that the code belongs to the original author, that they may
439not be on perl5-porters at any given time, and that a patch is not
440official unless it has been integrated into the author's copy of the
441module. To aid with this, and with points #1, #2, and #3 above, contact
442information for the authors of all contributed modules should be kept with
443the Perl distribution.
444
445Finally, the Perl community as a whole recognizes that respect for
446ownership of code, respect for artistic control, proper credit, and active
447effort to prevent unintentional code skew or communication gaps is vital
448to the health of the community and Perl itself. Members of a community
449should not normally have to resort to rules and laws to deal with each
450other, and this document, although it contains rules so as to be clear, is
451about an attitude and general approach. The first step in any dispute
452should be open communication, respect for opposing views, and an attempt
453at a compromise. In nearly every circumstance nothing more will be
454necessary, and certainly no more drastic measure should be used until
455every avenue of communication and discussion has failed.
3c78fafa 456
70e4a83b 457
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458=head1 DOCUMENTATION
459
460Perl's documentation is an important resource for our users. It's
461incredibly important for Perl's documentation to be reasonably coherent
462and to accurately reflect the current implementation.
463
464Just as P5P collectively maintains the codebase, we collectively
465maintain the documentation. Writing a particular bit of documentation
466doesn't give an author control of the future of that documentation.
467At the same time, just as source code changes should match the style
468of their surrounding blocks, so should documentation changes.
469
470Examples in documentation should be illustrative of the concept
471they're explaining. Sometimes, the best way to show how a
472language feature works is with a small program the reader can
473run without modification. More often, examples will consist
474of a snippet of code containing only the "important" bits.
475The definition of "important" varies from snippet to snippet.
1bb8a155 476Sometimes it's important to declare C<use strict> and C<use warnings>,
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477initialize all variables and fully catch every error condition.
478More often than not, though, those things obscure the lesson
479the example was intended to teach.
480
481As Perl is developed by a global team of volunteers, our
482documentation often contains spellings which look funny
483to I<somebody>. Choice of American/British/Other spellings
484is left as an exercise for the author of each bit of
485documentation. When patching documentation, try to emulate
486the documentation around you, rather than changing the existing
487prose.
488
489In general, documentation should describe what Perl does "now" rather
490than what it used to do. It's perfectly reasonable to include notes
491in documentation about how behaviour has changed from previous releases,
9e9fdd5d 492but, with very few exceptions, documentation isn't "dual-life" --
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493it doesn't need to fully describe how all old versions used to work.
494
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495=head1 STANDARDS OF CONDUCT
496
497The official forum for the development of perl is the perl5-porters mailing
498list, mentioned above, and its bugtracker at rt.perl.org. All participants in
499discussion there are expected to adhere to a standard of conduct.
500
501=over 4
502
503=item *
504
505Always be civil.
506
507=item *
508
509Heed the moderators.
510
511=back
512
513Civility is simple: stick to the facts while avoiding demeaning remarks and
514sarcasm. It is not enough to be factual. You must also be civil. Responding
515in kind to incivility is not acceptable.
516
517If the list moderators tell you that you are not being civil, carefully
518consider how your words have appeared before responding in any way. You may
519protest, but repeated protest in the face of a repeatedly reaffirmed decision
520is not acceptable.
521
522Unacceptable behavior will result in a public and clearly identified warning.
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523Repeated unacceptable behavior will result in removal from the mailing list and
524revocation of rights to update rt.perl.org. The first removal is for one
525month. Subsequent removals will double in length. After six months with no
526warning, a user's ban length is reset. Removals, like warnings, are public.
17c80487 527
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528The list of moderators will be public knowledge. At present, it is:
529Aaron Crane, Andy Dougherty, Ricardo Signes, Steffen Müller.
3b4ebcde 530
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531=head1 CREDITS
532
3b4ebcde 533"Social Contract about Contributed Modules" originally by Russ Allbery E<lt>rra@stanford.eduE<gt> and the perl5-porters.
3c78fafa 534