code: func (h *Client) DocumentReferrer(documentReferrer string) *Client {
  	h.documentReferrer = documentReferrer
  	h.documentReferrerSet = true
  	return h
  }
docs: // Specifies which referral source brought traffic to a website.
  // This value is also used to compute the traffic source. The
  // format of this value is a URL.