Sub-chapters are not collapsed when having headings

[jkr-ariel]

Problem

The chapter folding option does not behave as expected when having headings in the page being currently opened. When clicking the collapse button on the sidebar, only the headings are collapsed, leaving any sub-chapter expanded.

Steps

1. Create an empty directory: mkdir -p /tmp/testbook && cd /tmp/testbook
2. Init the book: mdbook init
3. Add the following to book.toml:

[output.html.fold]
enable = true
level = 0

4. Edit SUMMARY.md:

# Summary

- [Foo](./foo/index.md)
  - [Chapter 1](./foo/chapter1.md)
  - [Chapter 2](./foo/chapter2.md)

5. Create the files: mkdir -p src/foo && touch src/foo/{index,chapter1,chapter2}.md
6. Build the book and load up a browser: mdbook serve -o
7. The browser should be on the "Foo Index" page, and the subchapters are expanded,
8. Click the collapse button on the sidebar and notice that only the headings in "Foo Index" got collapsed.

Possible Solution(s)

No response

Notes

No response

Version

mdbook v0.5.0-alpha.1