WooCommerce日本語開発者向け情報サイト https://validator.w3.org/feed/docs/rss2.html checkout-flow-and-events filtering-payment-methods payment-method-integration README additional-cart-checkout-inner-block-types cart-line-items checkout-and-place-order-button coupons order-summary-items totals-footer-item README available-endpoints-to-extend extend-store-api-add-custom-fields extend-store-api-add-data extend-store-api-formatters extend-store-api-update-cart cart-coupons cart-items cart checkout-order checkout order product-attribute-terms product-attributes product-brands product-categories product-collection-data product-reviews product-tags products README additional-checkout-fields available-slot-fills checkout-utilities dom-events how-checkout-processes-an-order removing-checkout-fields README dom-events register-product-collection README README cart checkout collections payment query-state schema store-notices validation