I think the cause for header/footer tags is that there's no way for another program (like googlebot, browser extensions that use JavaScript to access the DOM, p

I think the cause for header/footer tags is that there's no way for another program (like googlebot, browser extensions that use JavaScript to access the DOM, page scrapers, etc) to figure out where the header and footer are. Sure, it's easy for you to figure that out if you wrote the page, but how does a program that's reading the page figure that out? I'm sure there are readability-like algorithms to figure this out, but I'd also imagine that they're not 100% accurate and need hints from the page's creator from time to time (just like readability).