Feature request: fragment-index for code-line-numbers

[maxpel]

One possibility to address the problem of setting fragment order easily in Rmarkdown for code-line-numbers, discussed here:

hakimel/reveal.js#3055 (comment)

Include a new option #| fragment-index: ""

```{r, echo=T}
#| fragment-index: "0"
#| code-line-numbers: "|1|2|3"
x <- 1:10
x
LETTERS[x]
```

This would set the "start" index of the first code highlighting fragment, which would already solve my use case, which would be going through code in one chunk with highlight fragments in one column, after all those fragments showing the plot output as a fragment in the second column and then displaying some text fragment in the first column below the code chunk.