<!DOCTYPE html> <!-- Any copyright is dedicated to the Public Domain. - http://creativecommons.org/publicdomain/zero/1.0/ --> <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>