RFC: MDX comment syntax

As part of #1039 comment syntax currently only supports JS comment expressions:

# Hello, world!

{/* I am a comment */}

This syntax is nice because it feels more JSX-y than HTML comments. However, it comes at a cost of interoperability with Markdown (which uses HTML comments).

I’m inclined to think ensuring that we also support HTML comments (despite it being a bit precarious to have multiple syntaxes) is worth it so that your average Markdown/README file works with MDX out of the box.

# Hello, world!

{/* I'm a comment */}
<!-- I'm a comment, too! -->

Anyone have any thoughts or opinions here?

[ChristopherBiscardi]

I agree

[leebyron]

I was also surprised by this and it posed a real barrier to adopting MDX for me (I have many existing markdown files with comments that I wanted to migrate to MDX and could not). So I wrote a plugin:

https://github.com/leebyron/remark-comment

I think I have an acceptable navigation of the whole “JSX is not HTML” issue:

• HTML comments cannot be included in JSX. Preserves the idea that JSX is just JSX.
• HTML comments are not emitted to the rendered output. This was always something I wanted my markdown renderer to do anyway, so I saw this as a side benefit. However this also side-steps the problem of trying to decide how to emit an HTML comment as a JSX node. It just does not.

I’d love to see this behavior built into MDX proper, but for now am working well, albeit with a more complex config, with this plugin.