code: def register_drops(self, dropin):
          
          drops = self.app.extensions['dropin'].setdefault(self.drops_type, [])
          drops.extend(self.load_drops(dropin))
docs: Register the `drops` in given `dropin` to a flask app.
  
          Args:
              app (Flask): the flask app to be initialized
              dropin (string): path of a python module or object, e.g. dropin.auth
  
  
          This is the only method that a drops loader **must** implment. The default
          behavior in the base loader is to store all the drops object in the app's
          extentions dict.
  
          For example, the drops with type `models` will be stored in a list which
          is accessible through::
  
              app.extensions['dropin']['models']
  
          or through DropInManager instance which provide a simple proxy to the dropin
          extension of `current_app`::
  
              dropin = DropInManager()
              dropin.models
  
          Whereas the BlueprintsLoader overrided this method to actually register
          the blueprints to the app.