wc-cart-checkout-classic

WooCommerce custom cart item data flows to order lines by hooking into checkout processing to copy cart values directly into WC_Order_Item_Product metadata, ensuring bespoke add-to-cart options persist at the line item level rather than as general order meta.

You add custom fees to WooCommerce classic cart totals by applying them within the correct WooCommerce fee hook during totals recalculation, which applies the surcharge safely without causing price mutation compounding across cart items.

WooCommerce HPOS requires special handling for order line item meta updates because direct post meta writes break the high-performance order storage architecture, meaning you must use HPOS-safe order APIs to update line item data during classic checkout processing.

You customize WooCommerce classic shortcode checkout fields by extending the checkout field array, adding server-side validation for the posted values, and ensuring the custom data maps correctly to the order without conflicting with the Checkout Block StoreAPI boundary.

WooCommerce cart items with custom add-to-cart options fail to merge correctly when cart item data hooks are not implemented properly, causing items to be treated as separate line items instead of merging when the custom identity parameters match.

The best way to mutate WooCommerce cart item prices dynamically is during the totals recalculation phase, applying absolute price mutations through the required cart hooks so the custom pricing updates accurately without multiplying or compounding the adjusted amounts.