Take this 
````markdown
---
title: test
format: 
  revealjs:
    slideNumber: 'c/t'
---

## slide 1

## Slide 2
````

It won't work as expected because Quarto is quoting and adding parenthesis `'(c/t)' `

````html
        // Display the page number of the current slide
        slideNumber: '(c/t)',
````

https://github.com/quarto-dev/quarto-cli/blob/d6a6f945df0fb1654942d13ec1e255db23e2e67d/src/format/reveal/format-reveal.ts#L46-L50

The parenthesis needs to be removed.

cc @apreshill I think this is the error you encountered
2021-07-26T12:59:38Z
cderv
closed
revealjs quoting of some option is not correct
https://github.com/quarto-dev/quarto-cli/issues/62