We use namespaces to delimit the visibility of functions and classes defined in the various subdirectories of the project. Namespaces provide a convenient layered structure to the project and we use them as a convention to signal which functions and classes are supposed to be used in any given layer. The top-level namespace is called pcm and includes all functions and classes that can be called from the outside world, i.e. a C++ API. Each subdirectory introduces a new namespace of the same name, nested into pcm. Code that can be used outside of a given subdirectory is put directly in the pcm namespace, i.e. the outermost layer. Finally, the namespace detail, at the third level of nesting, is used for functions and classes that are used exclusively within the code in a given subdirectory.