details and summary: expandable block with HTML

Useful to know

The <details> element creates a disclosure block, and <summary> provides its visible heading. The remaining content is shown when the block is open. For short supplementary information, this can replace a custom JavaScript mechanism. [1]

An example is <details><summary>What is included?</summary><p>Three files and instructions.</p></details>. The heading should indicate what will be revealed rather than simply saying “More”. This is a small illustrative component, not a description of a real product.