Currently this type of document will output resulting text without comment

````markdown
---
title: "Title"
format: 
  html: default
---

```{r}
1 + 1
```
````
![image](https://user-images.githubusercontent.com/6791940/138082612-e4053019-216d-488f-b0f3-a57b23a9e730.png)

This is different than with R Markdown but it stay readable. For reference, we have that with Rmd
![image](https://user-images.githubusercontent.com/6791940/138082796-7f8d1d62-a2ca-4160-9663-36aa34acfda2.png)

But when we add `collapse = TRUE`, I think we should add back a comment line. We get this with Quarto: 
![image](https://user-images.githubusercontent.com/6791940/138082896-994ee6e5-95cc-4c97-84e6-3a0f86527ed7.png)

And this with rmarkdown
![image](https://user-images.githubusercontent.com/6791940/138082982-b61cf0f4-b58d-41c5-9815-4306e6b6d9e0.png)


In quarto, source code is not really differentiable from resulting line. 

This is causing issue with highlighting too as with `collapse = TRUE`, everything is in one chunk. 

What about setting `comment = "#>"` or `comment = "##"` using an option hook when `collapse = TRUE` ? 

I can do a PR if that is ok.

Otherwise, we should maybe rethink the way `collapse = TRUE` is supported or not for Quarto.

2021-10-20T11:18:33Z
cderv
closed
Document with knitr engine and collapse = FALSE should probably have comment before text line
https://github.com/quarto-dev/quarto-cli/issues/140