code: func (h *Client) Affiliation(affiliation string) *Client {
  	h.affiliation = affiliation
  	h.affiliationSet = true
  	return h
  }
docs: // The store or affiliation from which this transaction occurred.
  // This is an additional parameter that can be sent when Product
  // Action is set to 'purchase' or 'refund'. For analytics.js
  // the Enhanced Ecommerce plugin must be installed before using
  // this field.