How exit is detected in a custom container extension?

[nerg4l]

Hello!

I recently inherited a project which relies on Parsedown to parse markdown documents. Currently the project is moving a lot of stuff to frontend and I'm considering making the markdown parsing to the frontend library (Svelte). For this I'm evaluating micromark and markdown-it.

The project relies on some custom markdown rules, let's call them "legacy flavor". Based on the documentation for this, the best case is to use custom extensions. Example:

• < text becomes a spoiler tag
• -> text aligns the text to right
• -^ text aligns the text to center
• -< text aligns the text to left

These are really close to how block quotes work in CommonMark so my idea was to start with the spoiler tag which closely resembles block quotes and gradually move forward to the "more advanced" rules. Unfortunately, I'm facing issues with the exit tag and to be honest the lack of resources on how to build block level extensions makes it a bit hard to figure things out. By reading the source code, I slowly make progress, but maybe someone from the community can give me a few tips.

First I created a few types.

export const spoilerTypes = {
	base: 'spoiler' as TokenType,
	prefix: 'spoilerPrefix' as TokenType,
	marker: 'spoilerMarker' as TokenType,
	prefixWhitespace: 'spoilerPrefixWhitespace' as TokenType
};

Then created an extension and constructor objects.

const spoilerConstruct: Construct = {
	name: 'spoiler',
	tokenize: tokenizeSpoilerStart,
	continuation: { tokenize: tokenizeSpoilerContinuation },
	exit
};

export const spoiler: Extension = { text: { [codes.lessThan]: spoilerConstruct } };

The rest matches block-quote.js but my code uses the previously defined types and codes.lessThan instead of codes.greaterThan. I can share my attempt if needed. To my surprise, exit id not called.

Can someone provide any guidance about where should I look? Any useful example which might help me better understand the logic?

[nerg4l]

I think I found the problem, I had to register a document extension.

export const spoiler: Extension = { document: { [codes.lessThan]: spoilerConstruct } };

[wooorm]

Also this sounds a lot like directives, so https://github.com/micromark/micromark-extension-directive might be of interest!