One of my favourite webpages. Have used it countless times over the years.

This also isn't complete because it doesn't show code between or around the various tables. I used to think of iptables as dumb filters that manipulate raw packets before/after the rest of the kernel sees them, but this view is wrong, and doesn't explain, for example, how it does NAT.

And the answer is it doesn't do NAT. The code is already preparing to do NAT, and that code merely consults the table to find out what kind of NAT it should do. The diagram makes it look like you can just move a NAT rule to a filter or mangle rule because the kernel just applies these tables in sequence anyway, but you can't because they are consulted by different blocks of code for different purposes.

I use this all the time when writing iptable rules.