code: func getCollectionForModel(model Model) (*Collection, error) {
  	typ := reflect.TypeOf(model)
  	for e := collections.Front(); e != nil; e = e.Next() {
  		col := e.Value.(*Collection)
  		if col.spec.typ == typ {
  			return col, nil
  		}
  	}
  	return nil, fmt.Errorf("Could not find Collection for type %T", model)
  }
docs: // getCollectionForModel returns the Collection corresponding to the type of
  // model.