code: function collection(id) {
      if(!this.resource) {
        throw new Error('This Entity does not have a Resource.');
      }
  
      var path = this.resource.path + '/collections';
  
      return Resource.constructorFactory(path, EVT.Entity.Collection)
        .call(this.resource.scope, id);
    }
docs: Custom nested resource constructor for Collections of a Collection.