woocommerce_purchase_order_item_types │ filter-hook │ WC 1.0

Usage

add_filter( 'woocommerce_purchase_order_item_types', 'wp_kama_woocommerce_purchase_order_item_types_filter' );

/**
 * Function for `woocommerce_purchase_order_item_types` filter-hook.
 * 
 * @param  $string 
 *
 * @return 
 */
function wp_kama_woocommerce_purchase_order_item_types_filter( $string ){

	// filter...
	return $string;
}

$string

-

Where the hook is called

$order->get_items( apply_filters( 'woocommerce_purchase_order_item_types', 'line_item' ) ),

$order_items           = $order->get_items( apply_filters( 'woocommerce_purchase_order_item_types', 'line_item' ) );

Where the hook is used in WooCommerce