Linux.com

If you look at the Free Software Foundations stance on what a derivative work, by extending Joomla's classes and making direct function calls into its API, the extension is a derivative work. The Lesser GNU Public License can be used by libraries and classes to allow non-free software to utilize them without being required to be licensed the same way. The GPL though, requires this. The question at hand is whether or not copyright laws support this claim, and that is something that is case by case and localized country by country. There is a great deal of ambiguity here, but by the traditional interpretation and the original spirit of the GPL, the 3rd party extensions licensed by a non-GPL compatible license is in violation of GPL.

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