Add support for posting with Markdown syntax

[jessicarod7]

Pitch

Requests to add support for posting with Markdown formatting has come up many times in the past, so this is a proposal to formalize the recent efforts. I'm not against other forms of markup formatting, but am focusing this issue specifically on Markdown.

My understanding is that Markdown support has not been fully approved or denied. The previous PR in #10787 (based on issue #853) seems to have been rejected due to issues in the implementation (and a somewhat derailed discussion). Issues #13544 and #21643 are similar, but cover subsections of this larger topic. I consider this a continuation of the conversation in #18958.

Two main points stand out:

• Is there general agreement to add Markdown support? I think clearing up this question first will avoid the conflicts that appeared in the rejected PR.
• If yes, how should Markdown be implemented?
  • Markdown flavour: Depending on the user, they might be coming from CommonMark, the GitHub-Flavoured derivative, Reddit (where New Reddit is different from Old), Misskey, Redcarpet, or the original spec, to name a few. One of these needs to be selected to avoid issues from mixing them.
  • Scope: Supporting all of Markdown would be a massive effort and massively increase risks of security vulnerabilities, so a subset of Markdown would be used. The rich text support added in Add support for incoming rich text #23913 is a good starting point.
  • Locations: In addition to posts, should support be added to other places, like profiles? A small point, but it can matter (ex. supporting Markdown in profile metadata, but not display names)

Motivation

With proper support for markup syntax, users can emphasize key points, format code snippets, create lists, or quote blog posts. It allows a message to be more expressive, similar to custom emojis. Adding support also means that users will no longer have to emulate the use of markup syntax:

I would like to make **this point clear.**

This means the content of the message is properly formatted into HTML, and can be interpreted by screen readers and other accessibility tools. It then displays as formatted on other servers, like Misskey and Akkoma.

Edit to quote a reply I made in the rich-text PR:

Agreed that HTML should remain the main way of transferring messages. When supporting other types of formatting, we should use the existing definition in the ActivityPub spec, section 3.3. The source field stores the original formatting, with a Content-Type like text/markdown, and then the posting client is expected to convert to HTML for the content field.

[jessicarod7]

Putting my personal opinion in a separate comment:

• I'm in favour of implementing Markdown for the reasons stated above.
• My implementation concept uses the parts of CommonMark that align with Add support for incoming rich text #23913. I would've preferred at least some size differential for header, keeping <h1> through <h6> the same size, but all slightly bigger than regular text. but I think it's a good starting point otherwise. I'm divided on whether tables should be added, but currently lean no.
• Supported locations would be posts and profile descriptions, but not display names or metadata (I think those should be kept relatively clean).

[AkazaRenn]

As the PR had mentioned it's now in the status of the "owner" of the project "compromising" to everyone else to allow some formatting to be shown in the posts but will never allow users to send them.

[fredster33]

I'd like to advocate for GitLab Flavored Markdown (GLFM).

[crse]

I support for compability with Misskey-flavored Markdown, as it will minimize broken post like this:

[quazar-omega]

Going for MFM seems overkill to me, I think Commonmark would fit quite well, also for ease of implementation by third-party apps

[awebeer256]

Going for MFM seems overkill to me, I think Commonmark would fit quite well, also for ease of implementation by third-party apps

I would've said that this is too cautious, but only because I had not known anything at all about MFM until seeing the post before yours. That seems, uh, extremely excessive 😱.

[quazar-omega]

Yeah lol. To be fair, though, plain Commonmark is a bit too restrictive, I don't know which other specification is more featureful without being too much, but I think there are extensions that add support for the few missing things that could be added in (strikethrough, tables, superscript and subscript, others?)

[Erlendms]

IMO we'd get so far with just

# heading
_italics_
**bold**
- Unordered lists
1. Ordered lists
> Block quote
[links](https://links.com)
code + code blocks

I like the idea of displaying h1-h6 as the same.

[ApolloFops]

IMO we'd get so far with just

# heading
_italics_
**bold**
- Unordered lists
1. Ordered lists
> Block quote
[links](https://links.com)
code + code blocks

I like the idea of displaying h1-h6 as the same.

I think supporting strikethrough could also be quite useful.

I think supporting ~strikethrough~ could also be quite useful.

[sloanlance]

I don't post on Mastodon as often as some people do, but when I do, it's fairly likely that I'll want to use Markdown formatting. Fortunately, I found that the client named Elk works well and it supports Markdown.

A recent post I wrote, using Markdown formatting for code segments (e.g., `None` → None) as seen in Elk: https://elk.zone/mastodon.social/@sloanlance/111537007812879508