System updates

[palexdev]

Can someone clarify this section of the documentation?

It is more convenient to upgrade and OTA; when upgrading KernelSU, you can directly install it in the manager without flashing manually; after the system OTA, you can directly install it to the second slot without manual flashing.

After the system OTA I can't install anything as I already lost root at that point. This sentence makes no sense to me? Can I make KernelSU survive system updates and what are the passages