Many languages have a place for these 'module level' comments. The ones that I know of: - Java has package-info.java - Scala has package.scala - JavaScript/T

Many languages have a place for these 'module level' comments. The ones that I know of: - Java has package-info.java - Scala has package.scala - JavaScript/TypeScript has the @file annotation in the doc comment at the top of the file - OCaml has the doc comment at the top of the file When you want to document an entire sub-system, it makes sense to put the documentation in that sub-system's root module.