code: func (c *Client) RegisterBlockEvent(filter ...fab.BlockFilter) (fab.Registration, <-chan *fab.BlockEvent, error) {
  	if !c.permitBlockEvents {
  		return nil, nil, errors.New("block events are not permitted")
  	}
  	return c.Service.RegisterBlockEvent(filter...)
  }
docs: // RegisterBlockEvent registers for block events. If the client is not authorized to receive
  // block events then an error is returned.