When chunk options start with `.`, e.g. `.value = "foo"`, they become part of the `.cell` fenced div. Then pandoc fails to render the fenced divs because `.value` is an invalid HTML attribute name.

Here's a very minimal and contrived reprex:

````markdown
---
title: "Reprex dots in chunk opts"
format: html
engine: knitr
execute:
  keep-md: true
---

```{r reprex, .test = "foo"}
runif(1)
```
````

The markdown and html output are

````markdown
::: {.cell .test='foo'}

```{.r .cell-code}
runif(1)
```

::: {.cell-output .cell-output-stdout}
```
[1] 0.9368014
```
:::
:::
````

![image](https://user-images.githubusercontent.com/5420529/165957331-40a92f03-346e-4a19-ade2-8c4899328c75.png)

Here's a less-contrived example where `.`-prefixed chunk options are used by a knitr language engine:

````markdown
---
title: "Reprex dots in chunk opts"
format: html
engine: knitr
execute:
  echo: false
  keep-md: true
---

```{r setup}
library(glue)
rand_5 <- function() signif(mean(runif(5)))
```

```{glue expected}
The average of 5 random numbers is {rand_5()}.
```

```{glue problem, .open = "{{", .close = "}}"}
The average of 5 random numbers is {{rand_5()}}.
```

```{glue user-fixed, .open = "{{", .close = "}}"}
#| output: asis
The average of 5 random numbers is {{rand_5()}}.
```
````

In this second example, there is an easy work around of adding `output: asis`, but that solution is probably unique to this use case.

![image](https://user-images.githubusercontent.com/5420529/165957881-8d9b05e3-271b-4c69-8e94-f033b88a4714.png)

2022-04-29T13:50:16Z
gadenbuie
closed
knitr chunk option that start with `.` break output
https://github.com/quarto-dev/quarto-cli/issues/762