Do <article> tags go inside of <sections> or the other way around?

html
#1

The answer is that it is totally up to you to use the tags as they make sense contextually. If you have many articles inside of a designated section, then it would make sense to nest it like this.

<section>
  <article></article>
  <article></article>
  <article></article>
</section>

If you have a large article with many content-specific sections in it, you can build it like that, too.

<article>
  <section></section>
  <section></section>
</article>

You can even have sections inside of an article inside of a section!

<section>
  <article>
    <section></section>
    <section></section>
  </article>
  <article>
    <section></section>
    <section></section>
  </article>
</section>

These tags are really just <div> tags renamed to make it easier to read the code and for screen readers and web crawlers to try and make sense of your page. The example in the textbook is just a sample.

Here is a relevant stack overflow