For some obscure reason some of the code fences in .mld files get tagged as reasonml. For example the last code fence of this section:

https://erratique.ch/software/brr/doc/web_page_howto.html#running

Here's the source:

https://github.com/dbuenzli/brr/blob/fc66944ba44bdd2fca6c35e8c82926e4890c7577/doc/web_page_howto.mld#L150