code: func (api *API) Index(ctx context.Context, indexName string) (*Index, error) {
  	span, _ := tracing.StartSpanFromContext(ctx, "API.Index")
  	defer span.Finish()
  
  	if err := api.validate(apiIndex); err != nil {
  		return nil, errors.Wrap(err, "validating api method")
  	}
  
  	index := api.holder.Index(indexName)
  	if index == nil {
  		return nil, newNotFoundError(ErrIndexNotFound)
  	}
  	return index, nil
  }
docs: // Index retrieves the named index.