If I add a notice to my user page that my answers are licensed under the GPL, in addition to the "standard" site-wide Creative Commons license, how does this affect posts by other users that I edit or other users that edit my posts?

Personally, I don't mind if others can use my code to write useful plugins or contribute to the official WordPress Codex. However, both places require the content to be licensed under the GPL. I could just add a notice to my personal user page, but of course, if I edit a post from another user, that should not automatically make the whole post from that user GPL-licensed.

How can I formulate the text so that it applies to my contributions, without incorrectly implying extra rights about contributions from other users?

My first attempt is this:

In addition to the standard Creative Commons license of this site, I give permission to use all my contributions under the GPL license (version 2). Feel free to re-use it in plugins, themes, or in the Codex.

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So what is the right way to declare the license for one's code posted on WPSE? I also try to state explicitly that all of my WordPress-related code content is licensed under GPL, so I would like to add this similar wording to my profile (or wherever). –  Chip Bennett Jun 6 '11 at 16:36
    
@Chip: I don't know what is the right way, but I updated the question with the notice that I currently use. Specifying "my contributions" is probably enough to make the distinction between the content from me and from other users. –  Jan Fabry Jun 6 '11 at 17:05
    
I want to make scope more broad and ask higher powers if there is possibility of establishing extended dual license, because of strong GPL flavor of WP ecosystem. At moment moving code in both directions (from WPSE to code and from code to post on WPSE) can be viewed as problematic in license aspects. –  Rarst Jun 6 '11 at 17:11
    
@Jan Fabry: ah, ok, so in the free-text info box in the profile. I'll add something to mine, too! –  Chip Bennett Jun 6 '11 at 17:21
    
I made mine simple and straight-forward: Note: all code posted by me, in questions, answers, or comments is licensed under GPL version 2.0 (or, at your option, any later version). –  Chip Bennett Jun 6 '11 at 17:24
    
@Rarst: That was also my ultimate goal, but I think we can show clear community support via these individual actions. I think the Drupal SE will also be interested in this. The trick is how to deal with historical contributions: you can't re-license them without the users agreement. –  Jan Fabry Jun 6 '11 at 17:29
    
Edited my license statement, in light of SE terms of service: Note: all code posted by me, in questions, answers, or comments is dual-licensed under the GPL version 2.0 (or, at your option, any later version), and the CC-By-SA license required by the Stack Exchange terms of service. –  Chip Bennett Jun 6 '11 at 17:33
    
Chip: I like your verbiage there. I'm adding it to mine as well. I always just assumed that since I was posting the code in an open forum, it was free to use. –  Norcross Jun 13 '11 at 12:58

3 Answers 3

A Word about Licensing

Licensing via the GPL isn't so much to protect our rights as developers but to protect the rights of people receiving our code. In a nutshell, it guarantees that anyone using our stuff has permission to do so, permission to change what we wrote, and permission to distribute those changes.

As far as I'm concerned, licensing code snippets here should follow the same model, if not a more permissive one. You're posting your code for all the world to see, and all the world should be able to benefit. If not, you should re-evaluate what you're posting and why.

Which License to Use

For most of my public code (i.e. the stuff I don't actually sell) I use the MIT license. It's actually less restrictive than the GPL as it's not viral, but still extends the same rights of use, modification, and redistribution. I've seen others claim their code snippets as published in the public domain in order to do the same - if it's owned by the public, the public can do whatever they want.

The thing to remember, though, is that content on this site is licensed under the Creative Commons Attribution-ShareAlike license (the cc-wiki logo in the bottom right corner). This license is not actually compatible with the GPL ... so unless you make other specific statements when you write code, technically people shouldn't be using your stuff in GPL'd plugins and themes anyway.

So if you want to be specific, make a comment whenever you post a code snippet explaining which license you're using with, perhaps, a link to a blog post or something explaining why. I personally recommend you use the most permissive license you're comfortable with. As I said, I use MIT for a lot of my stuff (so my name stays tied to my work), but some use public domain to cut out any illusion of restrictions.

Contributions From Others

Here's where the slippery slope begins. It's one thing to claim a license for your own work. But since others can modify your code on the site, they can (accidentally?) become contributors to your work. My argument would be that whatever license the original author applies to the code will be the binding one, and any later edits/contributions would fall under the same.

If an author isn't applying a license when they write code, then the CC BY-SA license for the entire site would likely apply. So if you're adding edits, revising code, changing formatting, etc, remember that your edits would be tied to the same.

This is where a generic "all my stuff is GPL" on your profile would do more harm than good. Yes, you might intend all of your code to be GPL, but you can't apply the GPL on code already licensed as CC BY-SA. So if you edit someone else's post, your code contributions there wouldn't be GPL and your catchall profile statement might lead someone down the road to think otherwise and unintentionally violate a license.

I would encourage including a single line of text with each GPL'd contribution just to keep things crystal clear:

This code snippet is licensed under the terms of the GNU GPL, version 3.

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Copyright is actually quite straight-forward: whomever originated a copyrightable work, and fixed it in a tangible medium, holds the copyright for that work, and thus holds exclusive rights to determine the license for that work. There is a problem, however: the SE terms of service state explicitly that subscribers agree that all posted content is licensed under CC-By-SA, with no apparent provision for dual-licensing. I agree with Rarst that this apparent discrepancy really needs to be addressed. –  Chip Bennett Jun 6 '11 at 17:30
    
@EAMann: I could do this for all substantial code snippets (smaller ones will probably be just citations), but I explicitly want to allow all non-code contributions to be included in the Codex. I want to use the "fire" from this community to improve the Codex. So then I would need to add this line to all my posts? –  Jan Fabry Jun 6 '11 at 17:32
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@Chip: I don't think it is a problem that the site states all your content is CC-by-SA. It is not an exclusive license, you are free to license it again under other conditions. You just can't take anything away from the CC-by-SA freedoms. –  Jan Fabry Jun 6 '11 at 17:42
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@Chip That statement in the terms of service doesn't prohibit dual licensing either. It's there to protect the SE network's right to distribute the content under CC-BY-SA, not to limit your right to distribute the work under other terms as well. –  EAMann Jun 6 '11 at 18:06
    
@Jan and @EAMann thanks; that makes perfect sense! –  Chip Bennett Jun 6 '11 at 18:49
    
@EAMann so your interpretation of that TOS page is that we're free to license our content under the GPL, but all content we post here is also licensed under the CC BY-SA license? Seems like there'd be a conflict there, since the CC BY-SA requires that all distributions retain the CC BY-SA license: If you alter, transform, or build upon this work, you may distribute the resulting work only under the same or similar license to this one. –  tnorthcutt Jun 13 '11 at 12:45
    
No, there's no conflict. Just as there's no conflict to my dual licensing my code as GPLv2 and GPLv3, even though the two versions are incompatible. The important thing to remember is that you are still the original owner of your content. By posting here, you're agreeing to license your content as CC BY-SA for the site (to protect it). But nothing restricts you from also licensing it as something else. –  EAMann Jun 13 '11 at 14:08
    
Remember, a dual license gives the licensee the choice of which terms to be bound under. To keep content free on a SE site, content needs to be available under CC BY-SA. So long as you allow the "or" when people use your stuff, you should be in the clear. –  EAMann Jun 13 '11 at 14:10
    
@tnorthcutt: If you dual-license your content, you give the user the option to choose one of the two licenses for your work. If they choose to use it under the GPL license, the CC BY-SA clauses don't apply, and vice-versa. So there is no conflict. –  Jan Fabry Jun 13 '11 at 14:29
    
@Jan: It seems odd to me that a user of this site (someone who has explicitly agreed to the TOS of the site) could do something (state that their content is licensed under the GPL) that would enable a scenario whereby the language of the TOS (which states that all work here is licensed under the CC BY-SA license) is voided. I think the TOS (and the licensing language used in it) override anything stated on this site by a user of this site. Just because we state that our work is licensed under the GPL doesn't mean the site operator agrees to that. –  tnorthcutt Jun 13 '11 at 19:02
    
@EAMann & @Jan: I'm not ruling out the possibility that you may be right (nor am I trying to be disagreeable). I do think that some 'official' clarification would be quite helpful on this issue, perhaps from @Jeff-Atwood. –  tnorthcutt Jun 13 '11 at 19:05
    
The TOS only state that all submitted content is licensed under CC BY-SA and that you grant the SE permission to use it. That license doesn't override other licenses I apply to my code, nor is it inherently removed if I choose to dual-license a snippet. It's a matter of me writing something, giving the SE permission to use/archive/distribute it under the terms of CC BY-SA, and explicitly giving developers the option to use it under the terms of the GPL/MIT/Apache/whatever license. Reread section 3 of the TOS ... –  EAMann Jun 13 '11 at 19:29

I would imagine that edits (for clarification, grammatical or typographical errors) do not constitute copyrightable content. Thus, the original author of such Questions/Answers retains full copyright over the work in question. In which case, the copyright license remains whatever the original author applies.

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As always when it comes to licensing issues:

(Disclaimer) I'm no lawyer, so this is just my personal opinion.

Currently no one can tell if everything WP related inherits the license. There are (loads of) different opinions about it. One of the strongest arguments out there is

that WordPress is a derivate of php and therefore should be under the same license, if any plugin, theme or else must inherit the WordPress license.

Try to get on the safe side and note it on your personal page. I haven't thought about it before (regarding my activities on this site), but I will add these lines right after I wrote this answer here.

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