Don't emit unnecessary classes in HTML tables

[ThomasSoeiro]

It is currently not possible to prevent pandoc from adding attributes to the HTML output from a Markdown input (e.g. .header, .odd, .even in the ReprEx below). It is only possible to drop attributes using filters.

Since both the CommonMark and GitHub Flavored Markdown specs do not mention default attributes in HTML output, shouldn't this be opt-in by default? Or possible to opt-out at least?

ReprEx

Using e.g. this input:

| foo | bar |
| --- | --- |
| baz | bim |
| baz | bim |

And converting to HTML using pandoc --from gfm --to html5, we get:

<table>
<thead>
<tr class="header">
<th>foo</th>
<th>bar</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td>baz</td>
<td>bim</td>
</tr>
<tr class="even">
<td>baz</td>
<td>bim</td>
</tr>
</tbody>
</table>

[jgm]

These are harmless; just don't add CSS rules that do things with them.

I don't think adding the option to avoid these is worth the increase in complexity.

[jgm]

Further note: the commonmark spec says

Note that not every feature of the HTML samples is mandated by the spec. For example, the spec says what counts as a link destination, but it doesn’t mandate that non-ASCII characters in the URL be percent-encoded. To use the automatic tests, implementers will need to provide a renderer that conforms to the expectations of the spec examples (percent-encoding non-ASCII characters in URLs). But a conforming implementation can use a different renderer and may choose not to percent-encode non-ASCII characters in URLs.

The spec is not about HTML output, it's about specifying how the commonmark document should be parsed into a structured document.

[ThomasSoeiro]

These are harmless; just don't add CSS rules that do things with them.

I agree this is not a big deal. However, these are common class names that are likely to be used elsewhere in a project. It would require to either drop them to reuse the class names, or use less meaninful class names.

[jgm]

Agreed -- we could use something like table-header, even-row, odd-row.
Of course, it would be a backwards-incompatible change, so I'm not sure it's a good idea.

[ThomasSoeiro]

My concern was for the sake of dropping "unecessary" classes to prevent name clashes since we can easely select .header using thead and .odd/even using variations of tbody tr:nth-child(2n).

Anyway, if you think theses classes are useful, you can close the issue as is.

Thanks a lot for your work on Pandoc!

[jgm]

My concern was for the sake of dropping "unecessary" classes to prevent name clashes since we can easely select .header using thead and .odd/even using variations of tbody tr:nth-child(2n).

This is true, though it wasn't in earlier versions of pandoc (when nth-child wasn't supported in CSS and we didn't put the header in thead!).

I think it might be worth stopping using these classes, and using the alternative you suggest instead.

[tarleb]

Could this be a "good first issue"?

[jgm]

Yes, it would be an easy one -- just have to change the HTML writer, the styles.html template, and some tests I think.

[ThomasSoeiro]

Could you point me to the HTML writer please?
(I'll have a look but I don't know Pandoc internals nor haskell...)

[jgm]

I think that if you can't find the HTML writer yourself, you're unlikely to be able to fix this issue, so I'll leave that as an exercise to the reader. :)