Enhancement request to expose H3 headings in the page TOC

[dipikabh]

Summary

The case for the page TOC ("In this article") to additionally show H3 headings in the page has been made here mdn/mdn-community#162. There is a consensus on the requirement.

Opening this issue so that the engineering team can plan this task. This might also require design inputs as highlighted in the discussion.

URL

An example link: https://developer.mozilla.org/en-US/docs/Learn/CSS/Building_blocks/Cascade_and_inheritance

Reproduction steps

Any and all pages on MDN contain the in-page TOC with only the H2 headings

Expected behavior

Both H2 and H3 headings in the page TOC

Actual behavior

The page TOC shows the H2 headings

Device

Laptop

Browser

Firefox

Browser version

Stable

Operating system

Mac OS

Screenshot

No response

Anything else?

No response

Validations

• I have read the Community Participation Guidelines.
• I have verified that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• I have checked that this is a concrete bug. For Q&A open a GitHub Discussion.

[wbamberg]

If you don't mind: I'd like to suggest if possible that rather than collapsing H2s that contain H3s, we consider making the ToC scrollable.

In most scenarios (outside mobile, and maybe even there) I think we will comfortably fit a ToC that contains H3 headings, and having them all visible makes it much easier to find things than having to expand H2s looking for them. Then scrolling the ToC should be a fairly rare fallback when the ToC is actually too long.

[wbamberg]

What is the status of this request, and how can it be triaged/moved foward?

I'm working on a page that discusses APIs that PWAs can use for background operation. It would make logical sense for some of the sections to be H3 headings, but that makes them non-discoverable in the current ToC implementation: mdn/content#25305 (comment).