Allow for `:::admonition` syntax (without curly brackets)

[choldgraf]

Right now our special admonition syntax uses the same curly-bracket structure that we use for directives. AKA:

```{note}
my note
```

is equivalent to

:::{note}
my note
:::

What do people think about supporting the Pandoc-style of admonition classes w/o curly brackets:

:::note
my note
:::

This could be a comma-separated list of admonition labels, so we could allow for :::note,admonition and this would behave like :::{note,admonition}.

One benefit of this would potentially be interoperability with other markdown specs. For example, in HackMD :::info blocks will render as special "info" blocks, whereas the curly brackets are a more MyST-specific thing so less likely to interoperate with other flavors of markdown.

[chrisjsewell]

I think if you want this it should work a bit like the code fences, in that they would be interpreted as a special case.

i.e.

we intepret

```python
...
```

as

```{code-block} python
...
```

note I was thinking of just making these ::: blocks act the same as ``` blocks, as in the content inside would not be parsed initially by the markdown-it-py parser, but in a recursive manner by myst-parser. Then they would just work for any directive (maybe making a special case for https://myst-parser.readthedocs.io/en/latest/using/syntax-optional.html#markdown-figures)

[choldgraf]

Yeah - so something like:

:::note
my note
:::

would be interpreted as

```{note}
my note
```

?

Another possibility is what we could make these behave the same as how Pandoc treats them (e.g. they become divs with classes in them), except for a few special-cases (like "note", "admonition", etc). However that is deviating even further from your ::: behaves the same as ``` vision :-/

I actually looked into the HackMD reference and it seems like it could be a nice reference to work from. It's all based on markdown-it extensions and they're all listed here:

https://hackmd.io/c/codimd-documentation/%2F%40codimd%2Fmarkdown-syntax

here's the one about their "container" behavior:

https://hackmd.io/c/codimd-documentation/%2F%40codimd%2Fmarkdown-syntax#markdown-it-container

Obviously we probably don't wanna just copy over the same extensions etc, but could be a nice comparison

[chrisjsewell]

yep there already a lot of these extensions in markdown-it-py/myst-parser 👍
see https://markdown-it-py.readthedocs.io/en/latest/plugins.html
or if there are more you see, add them to https://github.com/executablebooks/markdown-it-py/issues/23

[chrisjsewell]

note also parsing direct url links (like https://example.com) is coming soon: executablebooks/markdown-it-py#78

[chrisjsewell]

I'm closing this, because in #273 ::: now act exactly the same as ```, which precludes not having the curly braces