Advanced availability calculation

The advanced price modification present a powerful way to derive prices of the products in the feed, taking inputs from Shopify product price, compare at price, product and variant metafields in math expressions. 

By default, the availability in the feed are derived from product variant inventory using the following rule:

• If track inventory is not checked, or variant quantity is greater than 0, item is "in stock"
  
• Otherwise, if inventory policy is set to "continue", and there is a value set for the availability date, item stock status is "backorder".
  
• Otherwise, item status is "out of stock"

Do note that the variant quantity can be narrowed down to selected store locations, which is configured in the Metadata tab.

The default expression of availability is sensible for most use cases. However there are cases you might want to modify it. For example:

•  Make use of the "preorder" status in Google, with the status provided by a product metafield, and availability date from another.