code: func IsFatalError(err error) bool {
  	if e, ok := err.(interface {
  		Fatal() bool
  	}); ok {
  		return e.Fatal()
  	}
  	if parent := parentOf(err); parent != nil {
  		return IsFatalError(parent)
  	}
  	return false
  }
docs: // IsFatalError indicates that the error is fatal and the process should exit
  // immediately after handling the error.