Additional markdown headings in cell are ignored

Thanks again for the continued progress! I’ve noticed a regression – if a markdown cell in a notebook has more than one heading, for example:

# Level 1 heading
## Level 2 heading
# New level 1

Only the first Level 1 heading shows up in the TOC. It used to be the case that all headings were there, but now, to get them to show up, I have to split these markdown cells (into 3, for this example) so each has the heading as the first line of the cell. It would be nice if we were able to have the previous behavior back where all headings within a cell are captured.

[spencermathews]

I definitely appreciate that including all headers in a cell could lead to some complicated interactions with potential future features. Regardless of how that might be resolved, I would submit that including all headings in the TOC is simply the expected behavior, regardless of if they happen to be in the same cell.

[kenjioman]

I agree with the toggle feature.

A naive/ new user, I believe, will expect the table of contents to capture the full structure (headings/ sub-headings) of a document. Granted, going forward, document creators, knowing the limitation of jupyterlab’s TOC, can design their document with the constraint of having headings/sub-headings broken out into their own cells. However, the naive assumption will fail for past notebooks that weren’t designed this way.

I also recognize the desire for the collapse state from the TOC to propagate to what of the notebook is actually displayed as well (and the complexities this brings in the document model that kgryte mentioned above in https://github.com/jupyterlab/jupyterlab-toc/issues/54#issuecomment-553155370). In order to get the best of both worlds, I think a toggle would make sense – toggled one way, all headings show up, with collapse-ability turned off. Toggled the other way, notebooks sections can be hidden by TOC, but any additional headings don’t show up in TOC.

Granted, as a user that is not able to contribute to this feature request, I am fully appreciative of what has been done, what will be done, and design decisions made to simplify development 😃

Thanks again for all the awesome work with jupyterlab and TOC! This is a great contribution to the world: 🌎 🌏 🌍 😄