code: func (h *Client) ProductVariant(productVariant string) *Client {
  	h.productVariant = productVariant
  	h.productVariantSet = true
  	return h
  }
docs: // The variant of the product. Product index must be a positive
  // integer between 1 and 200, inclusive. For analytics.js the
  // Enhanced Ecommerce plugin must be installed before using
  // this field.