Incorrect format for HTML tables

[cderv]

Here is a minimal reprex

---
title: "table format"
output: html_document
---

```{r}
knitr::kable(iris, "html")
```

This is caused by the change in #1895 and the fact that kable html output does not include odd and even on rows.

Discovered by a user while loading kableExtra.

---
title: "table format"
output: html_document
---

```{r}
library(knitr)
library(kableExtra)
knitr::kable(iris)
```

kableExtra is modifying the format for knitr::kable that default to markdown pipe output. By auto formating to html, just loading the package modify the behavior of kable.

Two solutions:

• We could revert and fix another solution for Headerless tables not formatted correctly #1893
• Modify knitr html table to include the odd and even class.

For now the former seems better, as there is a JS solution for #1893 (see #1893 (comment))

cc @apreshill

[cderv]

In fact this is not a regression. knitr html table where not formatted as Pandoc Markdown table because the JS code does not target them.
With rmarkdown 2.4, before the aforementioned fix I thought was the cause.

That means HTML tables from knitr where not displayed the same as Pandoc markdown table and the fix in #1893 was not the cause.

This leave us with the question: Do we want knitr html table to be formatted the same as Pandoc mardown table ?

We may also add a test so that we are sure table existing framework are not impacted by our change... or is it something we should wait for revdep check to find out ?

[cderv]

Documentation: https://bookdown.org/yihui/rmarkdown-cookbook/kable.html#customize-html-tables

[yihui]

This leave us with the question: Do we want knitr html table to be formatted the same as Pandoc mardown table ?

That would be great. The only tricky thing is that the knitr html table doesn't have any special identifier or classes, so it may be hard to reliably detect tables generated by kable(, 'html'). Or perhaps we find out tables that do not have any attributes (id or class) at all and apply the table table-condensed classes? That might work.

If that still feels risky, users have to specify the class by themselves:

knitr::kable(, 'html', table.attr = 'class="table table-condensed"')

[cderv]

Or perhaps we find out tables that do not have any attributes (id or class) at all and apply the table table-condensed classes? That might work.

I thought of that, but we would for example target flextable output which have no class or id on theader or tbody also. I tried it, and the output changed.

Without adding id or class to knitr output, I guess we need to rely on the table.attr as I think there is not really a way for the boostrap style table to target the right table without id or class.

The previous change we made (from tr.header to tr.odd) seems more target to pandoc tables.

[yihui]

Okay, let's just have users use table.attr if they really want the table to be styled with Bootstrap.

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