How does \Magento\Sales\Model\Order\Shipment::register() work?

Context: How is «Submit Shipment» implemented?

958164/app/code/Magento/Sales/Model/Order/Shipment.php#L236-L268

/**
 * Registers shipment.
 *
 * @return $this
 * @throws \Magento\Framework\Exception\LocalizedException
 */
public function register()
{
	if ($this->getId()) {
		throw new \Magento\Framework\Exception\LocalizedException(
			__('We cannot register an existing shipment')
		);
	}

	$totalQty = 0;

	/** @var \Magento\Sales\Model\Order\Shipment\Item $item */
	foreach ($this->getAllItems() as $item) {
		if ($item->getQty() > 0) {
			$item->register();

			if (!$item->getOrderItem()->isDummy(true)) {
				$totalQty += $item->getQty();
			}
		} else {
			$item->isDeleted(true);
		}
	}

	$this->setTotalQty($totalQty);

	return $this;
}