<summary>

When to use it

First child of details, phrased so the closed state makes sense on its own.

When not to

No interactive content inside it (links/buttons in a summary fight the toggle), and only valid inside details.

Example

<details>
  <summary>Transcript</summary>
  <p>Welcome to the field guide…</p>
</details>

Authoritative references

• MDN: the <summary> element
• Specification entry
• See it used in context in the help center example