code: def layer(self, layer_name):
  		
  		if layer_name in self.__layers.keys():
  			return self.__layers[layer_name]
  		elif layer_name in self.__class__.__builtin_layers__:
  			return self.__class__.__builtin_layers__[layer_name]
  
  		raise RuntimeError('Invalid layer name')
docs: :meth:`.WMessengerOnionProto.layer` method implementation.