Re: Different comment syntaxes in within the same buffer?

On Fri, Apr 10 2026, Stefan Monnier via Users list for the GNU Emacs
text editor wrote:

>> I would like to ask the Lispers here whether there is a good solution
>> for having different comment syntaxes in the same buffer depending on
>> the point's position. For more context, a lot of web templating
>> languages (e.g., Svelte, Astro) have multiple syntaxes in the same file.
>> For example, Astro filles have a "frontmatter" section where JavaScript
>> can go, then after the frontmatter section goes CSS and/or HTML.
>
> Presumably you'd like Emacs to handle correctly not just the comments
> but also the highlighting of the rest, as well as the indentation,
> etc...
>
> IOW, you need a major mode that understands that the file is split into
> several sub parts each one using a different major mode.
> AKA "multi major modes".
>
> There are various packages that provide solutions for that, such as
> `mmm-mode` and `polymode`.
>
> The built-in `mhtml-mode` also does it for the specific case of HTML
> files including CSS and Javascript elements.

My specific case is that I'm using astro-ts-mode[1] for .astro files. So
although it can fontify the buffer just fine, it uses the same syntax
for comments regardless of where I am in it.

(If I could figure out how to have Emacs use a different comment syntax
when appropriate, then I was thinking I could open a PR to the package
maintainer to add the functionality.)

Ideally I'd use the existing astro tree-sitter grammar (rather than
`mmm-mode` or `polymode`, which I'm not familiar with) since it already
does its job well.


Footnotes:
[1]  https://git.isincredibly.gay/srxl/astro-ts-mode
-- 
Kind regards,
Kristoffer