What of the lowly page number

One interesting I've noticed in older books is that instead of page numbers (which are sort of like indices in an array), they used a system of writing the first word of the recto (right page) at the bottom right corner of the verso (left page) creating a linked list of sorts.

You can see some examples in this book https://archive.org/details/opticksortreatis1730newt (although it has page numbers too).

Those animated section separators (<hr>) are very distracting. Consider that someone might want to focus on the text!

I worked on page number extraction for a large online retailer. There were some amazing places they could be located. Stacked numbers indicating location in book/section/chapter, middle of the outside margin, mixed up based on if it was a title page or main body page.

What of the lowly Page Down key? It certainly can't scroll this website.