code: func RootError(ierr error) (nerr error) {
  	nerr = ierr
  	for i := 0; i < 20; i++ {
  		terr := unwrapError(nerr)
  		if terr == nil {
  			return nerr
  		}
  		nerr = terr
  	}
  	return fmt.Errorf("too many iterations: %T", nerr)
  }
docs: // Keep peeling away layers or context until a primitive error is revealed.