> if the software is not distributed/shared/used by others, then it might as well not exist
Even if it is used by the author/modifier in private? "others" != "everyone".
In your example, Wix could have kept the usage of GPL code internal to their organization and not have to publicly release anything. If they allowed others (i.e., outside their organization) to use the derived work, they'd have to provide the same users with the source code. Of course, in their case, they allowed the public to use the derived work, so anyone who used their service should be given the source.
> Also in my first comment, when I said "work" I was talking about the source code, not the software
I don't see how this changes anything.
Also, note that the GPL uses "work" to refer to the software (and to other forms of copyrightable works, as applicable) in both source material form as well as the compiled and linked forms.
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Judging from your views expressed here regarding the GPL, I strongly suggest you talk to a copyright lawyer, or at least read what copyright lawyers say the GPL and/or copyleft is: https://copyleft.org/guide/
Even if it is used by the author/modifier in private? "others" != "everyone".
In your example, Wix could have kept the usage of GPL code internal to their organization and not have to publicly release anything. If they allowed others (i.e., outside their organization) to use the derived work, they'd have to provide the same users with the source code. Of course, in their case, they allowed the public to use the derived work, so anyone who used their service should be given the source.
> Also in my first comment, when I said "work" I was talking about the source code, not the software
I don't see how this changes anything.
Also, note that the GPL uses "work" to refer to the software (and to other forms of copyrightable works, as applicable) in both source material form as well as the compiled and linked forms.
----
Judging from your views expressed here regarding the GPL, I strongly suggest you talk to a copyright lawyer, or at least read what copyright lawyers say the GPL and/or copyleft is: https://copyleft.org/guide/