Re: Different comment syntaxes in within the same buffer?

On Fri, Apr 10, 2026 at 12:02 PM Stefan Monnier via Users list for the GNU
Emacs text editor <[email protected]> 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.
>

We've done this to a large degree in the new `markdown-ts-mode`.  All
fenced code blocks are fontified in their mode using either treesit or
conventional font-lock and special handling for embedded markdown code
blocks and also modes like php-ts-mode which itself hosts many
subordinate treesit parsers.  We made it so that commands run in the
context of each code-block's mode with some hacking so
`indent-for-tab-command` `newline` etc., work.  It's not Van Gogh but it
mostly works, so a da Vinci.

The code has not yet been installed and is under discussion.  I can send it
to you or you can look on the list if you want to see how it works.