There is some debate about whether Wordpress plugins and Joomla extensions have to have a GPL compatible license.
The issue tends to get muddied because there are three issues rolled into one:
- Software licence – Does the GPL allow extensions or plugins to be developed using non-GPL licenses?
- Listing repository policies – Do the owners of the relevant extension/repository directories allow non-GPL licensed plugins or extensions?
- Trademark enforcement – Can the owners of the relevant trademarks prevent the trademarks being used in the names of extensions, domain names and other marketing materials?
GPL License and plugins extensions
The GPL license states:
These requirements apply to the modified work as a whole. If
identifiable sections of that work are not derived from the Program,
and can be reasonably considered independent and separate works in
themselves, then this License, and its terms, do not apply to those
sections when you distribute them as separate works. But when you
distribute the same sections as part of a whole which is a work based
on the Program, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it.
The Free Software Foundation (the GPL authors) believe that most plugins will be covered.
If the program dynamically links plug-ins, and they make function calls to each other and share data structures, we believe they form a single program, which must be treated as an extension of both the main program and the plug-ins. This means the plug-ins must be released under the GPL or a GPL-compatible free software license, and that the terms of the GPL must be followed when those plug-ins are distributed.
Joomla and Wordpress core developers also believe that plugins or extensions must be licenced under GPL.
This quote from Joomla FAQs:
It is our opinion that most extensions are derivative works of Joomla! and must be licensed under the GNU GPL. It is possible that an extension could work within Joomla! and not be considered a derivative work according to copyright law but this would have to be evaluated on a case-by-case basis. If you believe your extension is not a derivative work we strongly recommend that you seek professional legal advice.
There is an interesting thread on how the Joomla GPL policy has evolved at the Joomla Forums Be warned it will take a least a few hours to read it all!
See also comments about Wordpress plugins:
While others comments are that plugins are not required to licensed under GPL:
If you were hoping for a definitive answer then I have to let you down. It depends on how closely a plugin is integrated with the original system! A legal opinion is required.
Commercial decisions on repositories
The owners of the relevant repositories have complete commercial freedom to determine which plugins / extensions they will list in their repositories.
Both Joomla Extensions Directory and the Wordpress Plugins directory require submissions to be GPL compatible.
The impact for developers is that it will be hard to promote an extension without being listed on the relevant sites.
Use of trademark
Both Joomla and Wordpress restrict the use of their respective trademarks.
This may impact on your ability to use the trademarked words in domains, product names and marketing materials.
Joomla trademark restrictions FAQs
Wordpress domains policy
Discussion about Wordpress trademarks
You may be able to use trademarks under Fair Use of Trademarks rules. For example under Nominative Use you may refer to a trademark name as long as you don’t imply a relationship with the trademark holder.
DISCLAIMER: This article is not intended to give legal advice. If you have any questions about about usage of trademarks or licenses you should engage a lawyer to obtain advice specific to your circumstances
