code: func (h *Client) ProductCategory(productCategory string) *Client {
  	h.productCategory = productCategory
  	h.productCategorySet = true
  	return h
  }
docs: // The category to which the product belongs. Product index
  // must be a positive integer between 1 and 200, inclusive.
  // The product category parameter can be hierarchical. Use
  // / as a delimiter to specify up to 5-levels of hierarchy.
  // For analytics.js the Enhanced Ecommerce plugin must be installed
  // before using this field.