Railsのクラスパスについて

railsの中身をみてみようと思い、まずはappフォルダなどrailsの各フォルダを読み込む処理をしているところはどこか色々みてみた
まずはrails/railties/lib/rails/engine/configuration.rbのpathsメソッドに書いてあった。

def paths
  @paths ||= begin
    paths = Rails::Paths::Root.new(@root)

    paths.add "app",                 eager_load: true, glob: "*"
    paths.add "app/assets",          glob: "*"
    paths.add "app/controllers",     eager_load: true
    paths.add "app/helpers",         eager_load: true
    paths.add "app/models",          eager_load: true
    paths.add "app/mailers",         eager_load: true
    paths.add "app/views"

    paths.add "app/controllers/concerns", eager_load: true
    paths.add "app/models/concerns",      eager_load: true

    paths.add "lib",                 load_path: true
    paths.add "lib/assets",          glob: "*"
    paths.add "lib/tasks",           glob: "**/*.rake"

    paths.add "config"
    paths.add "config/environments", glob: "#{Rails.env}.rb"
    paths.add "config/initializers", glob: "**/*.rb"
    paths.add "config/locales",      glob: "*.{rb,yml}"
    paths.add "config/routes.rb"

    paths.add "db"
    paths.add "db/migrate"
    paths.add "db/seeds.rb"

    paths.add "vendor",              load_path: true
    paths.add "vendor/assets",       glob: "*"

    paths
  end
end

それとrails/railties/lib/rails/application/configuration.rbにもあった。

def paths
  @paths ||= begin
    paths = super
    paths.add "config/database",    with: "config/database.yml"
    paths.add "config/secrets",     with: "config/secrets.yml"
    paths.add "config/environment", with: "config/environment.rb"
    paths.add "lib/templates"
    paths.add "log",                with: "log/#{Rails.env}.log"
    paths.add "public"
    paths.add "public/javascripts"
    paths.add "public/stylesheets"
    paths.add "tmp"
    paths
    end
end

ふむふむ。。
最初のメソッドみていると、app以下にフォルダ作ってもパスを通すように見える。。