code: func Contents(filters ...Filter) ([]string, error) {
  	var result []string
  	err := ForEach(Sequence(filters...), func(s string) {
  		result = append(result, s)
  	})
  	if err != nil {
  		result = nil // Discard results on error
  	}
  	return result, err
  }
docs: // Contents returns a slice that contains all items that are
  // the output of filters.