A question about table rate module

[youcanget]

Hi, friends,

There are a function in file includes/modules/shipping/table.php,

  function quote($method = '') {
    global $order, $shipping_weight, $shipping_num_boxes, $total_count;

    // shipping adjustment
    switch (MODULE_SHIPPING_TABLE_MODE) {
      case ('price'):
        $order_total = $_SESSION['cart']->show_total() - $_SESSION['cart']->free_shipping_prices() ;
        break;
      case ('weight'):
        $order_total = $shipping_weight;
        break;
      case ('item'):
        $order_total = $total_count - $_SESSION['cart']->free_shipping_items();
        break;
    }
.............
.............

  }

I want to know which code will assign the value of$shipping_weight?