<!DOCTYPE html>
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<html>
<body>
<details open>
<summary>outer summary</summary>
<details open>
<summary>inner summary</summary>
<p>inner details</p>
<details open>
<summary>inner most summary</summary>
<p>inner most details</p>
</details>
</details>
<p>outer details</p>
</details>
</body>
</html>