An HTML disclosure widget in which information is visible only when the widget is toggled into an "open" state.
<details>[<summary>summary text</summary] >information text</details>
An optional summary can be provided using the <summary> element.
A disclosure widget is typically presented onscreen using a small triangle which rotates to indicate open/closed status.
If the first child of the <details> element is a <summary>, the contents of the <summary> element are used as the label for the disclosure widget.
<details><summary>[Click for spoiler]</summary>This text will only be revealed when you click to open</details>
<details> - Mozilla reference