code: static public function getClasses($type)
      {
          switch ($type) {
              case static::TYPE_FORM:
                  return [CartInterface::class];
              case static::TYPE_QUOTE:
                  return [QuoteInterface::class];
              case static::TYPE_PROFORMA:
                  return [QuoteInterface::class, OrderInterface::class];
              case static::TYPE_CONFIRMATION:
                  return [OrderInterface::class];
              case static::TYPE_VOUCHER:
                  return [];
              default:
                  throw new InvalidArgumentException("Unexpected type '$type'.");
          }
      }
docs: Returns the sale classes supported by the given type for document generation.
  
  @param string $type
  
  @return array