[YokoZar]

In general free open-source Wine has been developed with the philosophy of of not allowing application-specific code. Crossover (and presumably Photon), however, allows such patches for supported applications.

Patches can be motivated by specific apps, of course, but generally the requirement is to complete the patch implementing/fixing some API in a generic way, proven by additions to the test suite showing the same behavior on Windows.

[charcircuit]

The opposite it true too. Wine doesn't allow any code that isn't used. You have to find a specific app that uses it. If you don't know an app that calls a portion of a API you can not implement it even if the official documentation and behavior of using it on Windows makes it obvious how it should be implemented.

[bastawhiz]

That's pretty smart, though. There's no way to truly prove that the stuff you're implementing actually works if there's no software that runs it. Synthetic examples don't actually prove the API you implement works in a useful way for arbitrary software in the wild, it just proves that the pieces you've tested behave how you think they should.