Introduce leaf directives

[chrisjsewell]

background

Restructured text allow for the syntax:

.. note:: This is a short note

It is a nice, terse, one-line syntax for an admonition.

This comes at a price though; the parsing of a directive's "structure" is dependent on the type of directive.
Because the body content can possibly be on the first line, this does not work:

.. note:: I want a bespoke title

    Then some content

It is simply treated as a note with two body paragraphs
This means you then have to then use a different directive 😒:

.. admonition:: I want a bespoke title
	:class: note

    Then some content

https://github.com/executablebooks/MyST-Parse currently follows this logic with colon_fence, e.g.

:::{note} This is a body paragraph
this is a continuation of the same paragraph
:::

However, https://myst-tools.org/docs/mystjs/admonitions#admonition-titles does not

:::{note} This is the title
This is the body paragraph
:::

proposal

I propose "disambiguating" this difference, by introducing a "leaf div" to compliment the block "div"

::{note} This is a leaf div. It is interpreted as a single body paragraph,
that can continue on to multiple lines if really necessary

:::{note} this is a block div title
This is a block div content
:::

In executablebooks/mdit-py-plugins#72, I have sketched out what this would look like for a markdown-it plugin

Note with block attributes, you could also provide options to leaf divs, e.g. this

{#name .class key=value}
::{note} A note

would be equivalent to

:::{note}
:name: name
:class: class
:key: value

A note
:::

[chrisjsewell]

thoughts @rowanc1 ?

[rowanc1]

Intriguing, is that leaf div syntax used elsewhere?

I will get the proposal @mmcky and I are stewing on posted tomorrow. I think it complements this well, although it is smaller in scope -- only about the block title changes.

[chrisjsewell]

is that leaf div syntax used elsewhere?

Relatively similar: https://talk.commonmark.org/t/generic-directives-plugins-syntax/444
https://github.com/remarkjs/remark-directive

and then I also opened jgm/djot#215

[rowanc1]

I really like this for things like iframes, and fenced directives that @mmcky has introduced which don't have body content and should be a single line but end up being two.

[chrisjsewell]

which don't have body content and should be a single line but end up being two.

A trick thing here though is: do you interpret the content of a leaf div, as its body, or its argument? or have some way of discriminating the two?

For example, for admonitions we definitely want the content to be the body, but for other things like images you would want it to be the argument:

.. note:: The body that can have *nested syntax*

.. image:: path/to/image.png

you might even what these as separate (leaf) syntaxes, something like:

::{note} The body that can have *nested syntax*

..{image} path/to/image.png

So :: and .. (or some other character?) is similar to the discrimination between ::: and ```

[chrisjsewell]

Here I guess you would call ..{image} path/to/image.png a "leaf fence", i.e. the content is not interpreted as MyST

[chrisjsewell]

Just to be clear:

• ::{name} content would "equal" {"name": "name", "argument": None, "body": "content"}

• ..{name} content would "equal" {"name": "name", "argument": "content", "body": None}

and, well, if you just wanted {"name": "name", "argument": None, "body": None}, I guess you could use either in principal (but ..{name} would be recommended)

[chrisjsewell]

what do you think of that ☝️ @rowanc1 @mmcky

[mmcky]

Oh this is interesting for gated directives like {exercise-start} and {exercise-end}. I will think about these syntax ideas as for the gated directive case you want to add options but there may be a more compact way.

For example in the exercise case the pattern is often:

```{exercise-start}
:label: ex1
```

```{code-cell} python
<some code>
```

```{exercise-end}
```

So config/options/meta is more important in this case than content 🤔

https://ebp-sphinx-exercise.readthedocs.io/en/latest/syntax.html#alternative-gated-syntax

[chrisjsewell]

so then your example above would potentially go to:

{label=ex1}
..{exercise-start}

```{code-cell} python
<some code>
```

..{exercise-end}

[chrisjsewell]

what do you think of that ☝️ @rowanc1 @mmcky

gentle nudge @rowanc1 😉

[rowanc1]

Leaf directives are a cool idea, and allow for really terse syntax, which I think is awesome. I also really like the idea that they have almost the same syntax as a colon directive.

I think that we probably don't need a difference between parsing an argument vs parsing markdown, and we just do it in the same way that we don't have syntax differences between :::{figure} img.png and :::{admonition} _title_. This logic already has a precedence for living in the parser, not the syntax.

I like saying to a user, "want to do this on one line":

:::{note}
Hello note!
:::

"remove a colon, and put it on one line!" 💥

::{note} Hello note!

[chrisjsewell]

I think that we probably don't need a difference between parsing an argument vs parsing markdown...

This is not the difference, though, it's the difference between using the argument vs the body

Lets say you had a directive that could look like this:

:::{name} argument
body
:::

what does this represent?

::{name} text