code: func (s *Stack) similar(r *Stack, similar Similarity) bool {
  	if len(s.Calls) != len(r.Calls) || s.Elided != r.Elided {
  		return false
  	}
  	for i := range s.Calls {
  		if !s.Calls[i].similar(&r.Calls[i], similar) {
  			return false
  		}
  	}
  	return true
  }
docs: // similar returns true if the two Stack are equal or almost but not quite
  // equal.