This is a popular pattern in apps or other "frameworky" code, especially in C++.

I can think of at least two open source C++ apps I used where every time I checked in the IRC channel, the main dev wasn't talking about new app features, but about how to adopt even newer cooler C++ abstractions in the existing code. With the general result that if you want to know how some algorithm backing a feature works, you can't find it.