* Update: Tested up to WooCommerce 4.0.0.
* Fix: Script errors when multiple forms are on the same page.
* New: Quantity inputs are empty by default, use WC4 placeholders.
* New: Filter for getting the posted configuration.
* New: Dynamic filter for validating container based on context.
* New: Script supports passing custom configuration when triggering container update.
* New: Filter the child item's configuration data.
* Fix: Check child cart item is set in cart before accessing.