I’m just wondering, if I buy e.g. php based CMS from codecanyon with extended license, can I than make another script using the same source code and sell it on envato (e.g. classifields script based on the cms I bought)?
No. You would need explicit permission form the author (and extended licence).
Hi Charlie, thank you for your answer.
One more question, is that the same case with plugins/extension?
I mean, do I need authors approval for building an extension for his cms?
Yes basically you cannot use other scripts, plugins, themes etc form here in files for sale also on here without the right licenses and permission from the original author.
In some cases (e.g. big sliders) have their own license or agreements to use in themes etc. which ‘comes with permission’ to use it.
If in any doubt always double check things with the original author