Anyone can contribute to the documentation, the code, etc. You have to follow the procedures and rules but it's not some walled garden.

If someone needs a comprehensive 8 pages long explanation for what's exactly happening here, I recommend reading "Item 22: When using the Pimpl Idiom, define special member functions in the implementation file" from "Effective Modern C++" by Scott Meyers.

@SGaist
It happens even to the best ... at the very least we both support it, so that has to account for something ;)