### Bug description

By chance, [I stumbled across the fact](https://fediscience.org/@andrew/109730300221529378) that Quarto (at least as of v1.3.56) supports nested tabsets, where a document like this:

````
---
title: Tabsets inside tabsets
---

:::: {.panel-tabset}
## A section

::: {.panel-tabset}
### A section within a section

### Another section inside a section

Neato.

:::

## Another section
::::

````

…would render like this, with a tabset inside the parent tabset:

<img width="852" alt="image" src="https://user-images.githubusercontent.com/73663/214765075-c9703d09-f4f3-4912-9f7c-ebde3d62c8ef.png">

Somewhere between v1.3.56 and v1.3.129, though, this broke. Using v1.3.129, that same example document renders like this, only showing the parent tabset:

<img width="848" alt="image" src="https://user-images.githubusercontent.com/73663/214765412-87b9e435-3880-4c0d-8839-303ec6096584.png">

I'm not sure when/at which version exactly the regression happened, or if it even counts as a regression since nested tabsets were never formally documented and perhaps never meant to be supported? I think it is a useful to have in more complicated notebook-type documents (checking lots of Bayesian diagnostic plots for a bunch of models in a compact way, for example—[see here for another use case](https://fediscience.org/@andrew/109730391347236604))

---

(This is all with R 4.2.2 on macOS Ventura 13.1 with Quarto v1.3.129)


### Checklist

- [X] Please include a minimal, fully reproducible example in a single .qmd file? Please provide the whole file rather than the snippet you believe is causing the issue.
- [X] Please [format your issue](https://quarto.org/bug-reports.html#formatting-make-githubs-markdown-work-for-us) so it is easier for us to read the bug report.
- [X] Please document the RStudio IDE version you're running (if applicable), by providing the value displayed in the "About RStudio" main menu dialog?
- [X] Please document the operating system you're running. If on Linux, please provide the specific distribution.
cscheid
2023-01-26T05:38:31Z
andrewheiss
bug regression tabsets
v1.3
closed
Nested tabsets no longer work
https://github.com/quarto-dev/quarto-cli/issues/4104