[Request] Persisting class names inside <pre>

[daniyalhamid]

Is your request related to a specific problem you're having?
A clear and concise description of the problem itself. Ex. I'm always frustrated when [...]

There should be an option perhaps to persist existing class names inside pre / code tags, for example:

<pre>
const foo = <span class="wavy-error">bar</span>;
</pre>

The solution you'd prefer / feature you'd like to see added...
Allowing certain class names to be persisted and not removed when parsing happens would be a great addition.

Any alternative solutions you considered...
I tried creating a custom plugin for this, but can't figure out much with limited documentation on the subject.

Additional context...
The desired result I'm trying to achieve is like the following screenshot:

If it's already possible somehow to persist a class name, I'd really appreciate some guidance.

[joshgoebel]

This once upon a time was a feature, it's since been removed. This is a feature most users do not need and it only increases the risk that 99% of users shoot themselves in the foot introducing HTML/JS injection security issues - to assist the 1% of users who could benefit from this feature. Simply disallowing this entirely allows us to make it easier to catch these vulnerabilities during development - rather than after a project goes into production.

Ref: #2889

This can be done easily enough using a plugin (capture HTML before highlight, carefully re-insert it after) - someone just needs to step up to write/maintain it. The old code may or may not still work and is not supported.