Some code blocks are always detected as JSX

[alecmev]

By the way an user reported that some code blocks languages were always detected as jsx, it would be cool to list all available languages in the docs and default to no language by default

I assume now the language is detected from the class of the code tag

Originally posted by @remorses in #132 (comment)

[alecmev]

Yep, the language is extracted from the class (via some heuristics), but the fallback should be Markdown (essentially plain text). Can you share a sample HTML value of the code block that's being detected as JSX?