code: func WrappedErr(err error) error {
  	cast, ok := err.(*Error)
  	if !ok {
  		return err
  	}
  	return cast.WrappedErr()
  }
docs: // WrappedErr returns the wrapped error, if the current error is simply
  // wrapping some previously returned error or system error. If the error isn't
  // hierarchical it is just returned.