section, article, and aside

The section, article, and aside elements are often confused because all three can contain headings and paragraphs. Their purpose is different.

• article represents a self-contained composition that could make sense independently, such as a news story, forum post, or product review.
• section groups content by a common theme, usually with a heading.
• aside contains content that is related but not central to the main flow, such as a sidebar note or related links.

<main>
  <article>
    <h1>How browser caching works</h1>
    <p>...</p>
    <section>
      <h2>Freshness and revalidation</h2>
      <p>...</p>
    </section>
  </article>
  <aside>
    <h2>Related reading</h2>
    <a href="/guides/http/">HTTP basics</a>
  </aside>
</main>

A section should have a reason to exist beyond styling. If you only need a wrapper for CSS or scripting and the content has no distinct theme, a div may be the better choice. An article can contain sections when the relationships make sense.