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