How does reading mode work in browsers?

Question

Google Chrome

How does reading mode work in browsers?
1) The browser itself analyzes the site, finds the main article and removes everything superfluous: advertising, sidebar, menu, etc.? Or do website developers prepare ahead of time with markup and the like?
2.1) If the first option, how does the browser parse?
2.2) Where can I read about this markup?

Answer 1

Using the correct markup, browsers themselves choose what to show them in reading mode. And here is an article for a more detailed deepening into this matter.