I've only tested this in Edge and IE, but using this polyfill turns this:
<details open>
<summary>Open details</summary>
Show raw text<span> and text in elements</span>.
</details>
<details>
<summary>Closed details</summary>
Show raw text<span> and text in elements</span>.
</details>
Text outside the details.
into this:
▼Open details
Show raw text and text in elements.
►Closed details
Show raw text.
Text outside the details.
instead of the expected:
▼Open details
Show raw text and text in elements.
►Closed details
Text outside the details.