Hi all. I am new in licensing. I read more then 20 article and i have still have question about GPL.
Q 1 - Can i use any theme in the wp.org as a starting theme? Off course i don’t use css and images. and link credit in the license text
Q 2 - Some themes on the themeforest have 100% GPL license. Can i integrate their header builder to my theme?
Q 3 - I know HTML and PHP are freely use but what about JS?
Thank you 
GPL means you can use the code in both commercial and free projects only in one condition keep the original author credit some how.
If any theme or plugin states that it is 100% GPL, you can use it to build anything you want either from personal or commercial perspective.
You can use parts or all of a GPL product but:
You cannot take parts or in whole of a 100% GPL item found in the marketplace here and use it to build something to resell here. This is the marketplace protecting it’s authors, so if this is what you intend to do, then don’t.
For personal/commercial use outside this marketplace, it’s fine.
But the author give away their code rights under GPL, why envato protect their right? Could you send a quote from envato policy?
Envato should protect their graphics, design and that’s it. If envato support 100% GPL and the product itself give their right, envato respect own author decision.
To be honest I’d like to believe that no marketplace worth their salt would allow someone other than the creator of a theme or plugin to sell it. Certainly at ThemeForest we would prohibit anyone trying such a thing.
Thank you Typps. If you know about GPL could you please tell me, is this against GPL? You may be say “Envato say whatever they want”, but you can’t change the rules for your own. GPL is GPL. Code is FREE to use anywhere for any purpose.
BTW, i am not going to take any code from themeforest. At first, this is not ethical for me. but it can be possible.
Haven’t you ever used a jQuery plugin inside your themes ? If you did then you used such a plugin to create something entirely different which is not against GPL rules however lets say you used GPL jQuery plugin to build on top of it other jQuery plugin this case is not againest GPL as well only if you are going to release your new plugin under GPL
When money is concerned, do not blindly invest your time into creating something based on someone elses code. Especially when the license is GPL. It’s viral nature can have several implications.
Whatever the license says, always contact the creator, the person that wrote the code and ask them for permission.
Sometimes, they may even relicense it to you under more favorable terms for a small fee 