Make sections foldable (collapsible headings)

[biva]

Spoilers/foldable details sections are tracked separately in #3646

This ticket remains about making existing sections like headings foldable.

Initial report

Is your feature request related to a problem? Please describe.
For large pages, it is hard to have a vision of the structure, or to navigate within the page to find the right section / paragraph.

Describe the solution you'd like
It would be great to be able to collapse (fold) and open (unfold) sections, thanks to a small arrow on the left. Sections would be based on headers (H1, H2, ...), with subsections that would also be collapsible (foldable). In addition, a button on the top would fold/unfold all.

Describe alternatives you've considered
Having a menu on the top or on the right sidebar (also with collapsible sections)

Additional context

• An example is described in the following link: https://gist.github.com/pierrejoubert73/902cc94d79424356a8d20be2b382e1ab
• Microsoft describes its own solution here: https://support.microsoft.com/en-us/office/video-collapsible-headings-c7b03e92-a397-479d-b989-57393daf2d65
• This other issue mentions a collapsible section for a specific file type: Support Frontmatter in MD files #145

[rinurinu]

I would love either this or the headline overview from the other issue being implemented (or both).

[max-nextcloud]

Thanks for proposing this.
As the outline view has been added now and provides an alternative way to achieve the same goals i'll close this issue.

[mejo-]

Well, to be honest we had this feature on our feature planning whiteboard recently and I agree that it's a useful one. So maybe let's keep this open? 😁

[luka-nextcloud]

There are 2 things to be added:

1. Collapsible sections #3646
2. Add collapse function on headings (like https://support.microsoft.com/en-us/office/video-collapsible-headings-c7b03e92-a397-479d-b989-57393daf2d65)

• steps:
  • Add toolbar item to fold/unfold all headings
  • Add fold/unfold functions on every headings
  • Handle copy/paste a folding heading
• issues to consider:
  • Only support folding on H1 level or all heading levels?
  • press "Enter" at the end of folding heading should force new line to have same heading level?

[juliushaertl]

You're right I totally missed #3646, let me actually extract the first part of this ticket and the discussion and move over to that one.