Clean Room Guidelines
Wine developers often run into undocumented behavior or interfaces in Windows. When this happens, they use clean-room design techniques to work around the problem without infringing on any Microsoft copyrights.
Here are some techniques believed to be safe for Wine contributors:
- When trying to understand a Windows API function, write a test program that verifies its behavior, and contribute it to Wine's conformance test suite.
- It's also ok to look at MSDN (but take it with a grain of salt).
- But play it safe - if a test program will do, don't look at any Microsoft doc or headers.
- When in doubt, ask on the wine-devel mailing list!
Here's a short list of things for Wine contributors to avoid. It is by no means a complete list; all contributors need to be thoughtful about copyrights and avoid violating any law.
- Don't write a test program that prints out the values of an internal table.
- Don't disassemble Microsoft code.
- Don't look at any Microsoft source code, even if it's made "public" under some license, e.g. don't look at the C runtime library source code that ships with their C compiler. Note that as an exception, code that is released under the MIT license (or another LGPL-compatible license) is OK to look at and copy from (with proper attribution).
- Don't use +relay with native components. In general, try to avoid debugging with native components, as that leaks information about what function calls those components make.
- Don't examine debug symbols for Microsoft code.
- Don't look at ReactOS code either (not even header files). A lot of it was reverse-engineered using methods that are not appropriate for Wine, and it's therefore not a usable source of information for us. 
"For what it's worth, the policy I've personally been using has been to simply avoid unnecessary risk."