<!-- normal --> <details> <summary>Summary of details</summary> Details content. </details> <!-- open --> <details open> <summary>Summary of details</summary> Details content. </details>
Those three details elements could be open by default, and the user would have to deselect the option, or not.
My OS is Debian 10 (Buster); my perl versions are 5.28.1 local and 5.16.3 or 5.30.0 on web host depending on the shebang.