Question about the app module declaration

[nikmartin]

I'm curious about this code:

angular.module('popup', [
  'popup.services',
  'popup.controllers'
]);

Where does the dotted notation for the module dependencies come from, and what does it reference? There are no modules named 'services' or 'controllers', only folders inside /app that bear those names. Is this some type of folder level dependency injection I'm not aware of, or is this a bug? It doesn't actually seem to need any dependency injections, since the Controller is defined inside popup.html:

 <div ng-controller="MainController">