code: func (h *Client) CheckoutStep(checkoutStep int64) *Client {
  	h.checkoutStep = checkoutStep
  	h.checkoutStepSet = true
  	return h
  }
docs: // The step number in a checkout funnel. This is an additional
  // parameter that can be sent when Product Action is set to
  // 'checkout'. For analytics.js the Enhanced Ecommerce plugin
  // must be installed before using this field.