Some project like Wine forbids you to contribute if you ever have seen the source of MS Windows [1]. The meatball inside your head is tainted.
I don't remember the exact case now, but someone was cloning a program (Lotus123 -> Quatro or Excel???). They printed every single screen and made a team write a full specification in English. Later another separate team look at the screenshots and text and reimplement it. Apparently meatballs can get tainted, but the plain English text loophole was safe enough.
[1] From https://gitlab.winehq.org/wine/wine/-/wikis/Developer-FAQ#wh...
> Who can't contribute to Wine?
> Some people cannot contribute to Wine because of potential copyright
violation. This would be anyone who has seen Microsoft Windows source
code (stolen, under an NDA, disassembled, or otherwise). There are some
exceptions for the source code of add-on components (ATL, MFC, msvcrt);
see the next question.