@snusnu this is a tiny point, but @mbj and I have been actually been dropping the "class" and "module" prefixes and writing these as:

```ruby
  end # Mapper
end # ROM
```

@mbj made the argument to me that he sometimes flips something from a module to a class, and it's easy to overlook the comment and get things out of sync. The main reason we do this is that when we're in a file with a bunch of class declarations, and especially inner classes, we can visually identify where a class or module beings and ends; the type itself is not so important, the name is really all we need.