How could licences be chosen to allow this?
As an example, how are things done with paid addons with Prestashop?
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Sign up to join this communityHow could licences be chosen to allow this?
As an example, how are things done with paid addons with Prestashop?
According to the GNU Licenses FAQ here and I quote
However, in many cases you can distribute the GPL-covered software alongside your proprietary system. To do this validly, you must make sure that the free and non-free programs communicate at arms length, that they are not combined in a way that would make them effectively a single program.
So I think you can combine it with proprietary as long as it's in an arms length.
For eg, Plugins/Add-ons, but make sure the core working of your program is not completely depended on that plugin.
Some Open source licenses such as MIT or BSD does allow you to sub-licensing.
Again it depends on what license is used.
Disclaimer: I'm just a programmer, not a laywer.