>> Do we still need such complicated functions as
>> mhtml-ts-mode--language-at-point, js--treesit-language-at-point, etc.
>> that duplicate the rules from 'treesit-range-rules'
>> when now the default language-at-point function could be implemented
>> just as
>> 
>>  (treesit-parser-language
>>   (or (seq-some (lambda (o) (overlay-get o 'treesit-parser))
>>                 (overlays-at (point) t))
>>       treesit-primary-parser))
>
> Yeah, we can provide a default language-at-point function now that
> determines the “most relevant parser” by embed level. But we should keep
> treesit-language-at-point-function because a) it’s already in a release
> version and b) we want major modes to be able to customize what parser to
> pick at any given point.

Ok, so here is a complete patch: