# How to keep giallo from rewriting unknown langs to "plain"

**URL:** <https://zola.discourse.group/t/how-to-keep-giallo-from-rewriting-unknown-langs-to-plain/2906>\
**Category:** Support\
**Created:** [February 20, 2026, 10:34am UTC](https://zola.discourse.group/t/how-to-keep-giallo-from-rewriting-unknown-langs-to-plain/2906 "2026-02-20T10:34:33Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![penryu](https://yyz2.discourse-cdn.com/free1/user_avatar/zola.discourse.group/penryu/32/1586_2.png) [@penryu](https://zola.discourse.group/u/penryu)\
**Post date:** [February 20, 2026, 10:34am UTC](https://zola.discourse.group/t/how-to-keep-giallo-from-rewriting-unknown-langs-to-plain/2906/1 "2026-02-20T10:34:33Z")

</div>

**Background**

I use a third-party library Klipse (link below) to augment code blocks for some languages, usually JavaScript and Clojure. It uses CSS selectors to find specific code blocks in a page and attaching dynamic logic to them. I was using it under Cryogen when I came over to Zola.

In previous versions of Zola, the old highlighting engine would take whatever string I put next to the markdown codeblocks and use it as a CSS class name for the rendered element.

Eg, this content:

````markdown
```klipse-js
var flooble = "whatsit";
```

````

Would create the following HTML when rendered:

```xml
<pre class="language-klipse-js" data-lang="klipse-js">
    ...
    <code class="language-klipse-js" data-lang="klipse-js">...</code>
    ...
</pre>

```

This allowed me to use the CSS selector `.language-klipse-js` in my config to let Klipse find my code blocks.

I don’t think this was ever officially supported, but it was convenient for my purposes, and everything worked.

**How It’s Going**

As the release notes and docs describe, the old highlighting engine has been replaced by a new crate, `giallo`, and it’s working very well for normal highlighting.

I could even use a different CSS selector to use the `data-lang` attribute instead of the `class`, except that Giallo is picky about languages it doesn’t support.

If I set `error_on_missing_language = false`, and try to use languages like `klipse-js` again, it silently rewrites the `::before` headers to `PLAIN`, and changes the tag attributes to `data-lang=”plain”` as well.

**My Workaround**

I’m currently able to work around this by creating dummy grammars for the bogus languages like this:

```json
// extra_grammars/klipse-js.json
{"name": "klipse-js", "scopeName": "source.js"}

```

It doesn’t do much, obviously but it’s the bare minimum JSON required to declare a grammar, so that giallo doesn’t rewrite it to `plain`.

**The Request**

Like I said, this is a functional workaround, but it’s really fragile and requires me to create 20+ dummy grammar files for each langauge the Klipse library supports.

Is there a way to prevent Giallo from rewriting unrecognized/unknown languages to “plain”? A configuration option I haven’t been able to find?

If not, is there any interest in supporting this? Something like

```ini
[markdown.highlighting]
rewrite_unknown_languages_as_plain = true

```

…or something, that defaults to `true` but can be disabled?

I may even be able to help implement and/or test it if there this sounds useful, but wanted to gauge interest before dropping a PR in people’s laps.

The Klipse repo can be found here: [https://github.com/viebel/klipse](https://github.com/viebel/klipse)

And you can see it in action here (via an older build of Zola): [Give Me a Sine | lexical snark](https://lex.pun.ninja/give-me-a-sine/)

Thanks for your time! And thank you for such an amazing framework!

-Tim

---

<div class="post-metadata">

**Author:** ![keats](https://avatars.discourse-cdn.com/v4/letter/k/34f0e0/32.png) [@keats](https://zola.discourse.group/u/keats)\
**Post date:** [February 20, 2026, 11:14am UTC](https://zola.discourse.group/t/how-to-keep-giallo-from-rewriting-unknown-langs-to-plain/2906/2 "2026-02-20T11:14:56Z")

</div>

You can pass any metadata to the markdown fence and it will pass that as data- attributes on the `<code>` element. so you can do

````auto
```klipse=js
my code here
```

````

it will mark it as plain so no highlighting but you can then get the `data-klipse=”js”` attribute on the code

---

<div class="post-metadata">

**Author:** ![penryu](https://yyz2.discourse-cdn.com/free1/user_avatar/zola.discourse.group/penryu/32/1586_2.png) [@penryu](https://zola.discourse.group/u/penryu)\
**Post date:** [February 20, 2026, 2:03pm UTC](https://zola.discourse.group/t/how-to-keep-giallo-from-rewriting-unknown-langs-to-plain/2906/3 "2026-02-20T14:03:04Z")

</div>

Oh! That is beautiful!

I didn’t notice at first that you wrote `klipse=js` instead of `klipse-js`, but I can confirm it _does_ create a `data-klipse=”js”` attribute!

THANK YOU!

**For others trying to integrate Klipse with Zola v0.22+, here’s what I’ve done and confirmed works.**

For the markdown fence, I’m using:

````markdown
```clj,klipse=cljs
(defonce an-atom (atom 1))
```

```js,klipse=js
const stuff = ['thing1', 'thing2'];
```

````

This way it gracefully falls back to giallo’s highlighting if the client has javascript disabled.

For the CSS selector, I’m matching on the outer `<pre>` tag, so I used selectors of this form in the klipse config:

```javascript
selector: 'pre:has(code[data-klipse="cljs"])',
selector_eval_js: 'pre:has(code[data-klipse="js"])',
// etc.

```

Thank you so much for your help, @keats!  
-Tim