I don't see any mention in that entire wiki page of marking the edges of pages vertically for reference when looking at the book from the side. In fact it flat

I don't see any mention in that entire wiki page of marking the edges of pages vertically for reference when looking at the book from the side. In fact it flat out misses it in the examples, "pointers are typically page numbers, paragraph numbers or section numbers" all of which require you to flip through pages manually instead of just looking at the side and getting a visual.