markdown-it/docs/development.md

# Development recommendations

Prior to continue, make sure you've readed:

1. [README](https://github.com/markdown-it/markdown-it#markdown-it)
2. [API documentation](https://markdown-it.github.io/markdown-it/)
3. [Architecture description](architecture.md)


## General considerations for plugins.

1. Try to understand, where your plugin rule sould be located.
  - Will it conflict with existing markup (by priority)?
    - If yes - you need to write inline or block rule.
    - If no - you can morth tokens in core chain.
  - Remember, that tokens morphing in core is always more simple than writing
    block / inline rules (if you don't copy existing one). However,
    block & inline rules are usually faster.
  - Sometime it's enougth to modify renderer only (for example, to add
    header IDs or `target="_blank"` for the links).
2. Search existing
   [plugins](https://www.npmjs.org/browse/keyword/markdown-it-plugin)
   or [rules](https://github.com/markdown-it/markdown-it/tree/master/lib),
   doing something similar. It can me more simple to modify existing code,
   instead of writing all from scratch.
3. If you did all steps above, but still has questions - ask in
   [tracker](https://github.com/markdown-it/markdown-it/issues). But, please:
   - Be specific. Generic questions like "how to do plugins" and
     "how to learn programming" are not accepted.
   - Don't ask us to break [CommonMark](http://commonmark.org/) specification.
     Such things should be discussed first on [CommonMark forum](http://talk.commonmark.org/).


## Notes for NPM packages

To simplify search:

- add to `package.json` keyswords `markdown-it` and `markdown-it-plugin` for plugins.
- add keyword `markdown-it` for any other related packages.


## FAQ


#### I need async rule, how to do it?

Sorry. You can't do it directly. All complex parsers are sync by nature. But you
can use workarounds:

1. On parse phase, replace content by random number and store it in `env`.
2. Do async processing over collected data.
3. Render content and replace those random numbers with text
   (or replace first, then render).

Or you can render html, then parse is to DOM (or
[cheerio](https://github.com/cheeriojs/cheerio) AST) and apply transformations
in more convenient way.


#### How to replace part of text token with link?

Righ sequence is to split text to several tokens and add link tokens between.
Result will be: `text` + `link_open` + `text` + `link_close` + `text`.

See implementations of [linkify](https://github.com/markdown-it/markdown-it/blob/master/lib/rules_core/linkify.js) & [emoji](https://github.com/markdown-it/markdown-it-emoji/blob/master/lib/replace.js) - those do text token splits.

__Note.__ Don't try to replace text with html markup! That's not secure.


#### Why my inline rule is not executed?

Inline parser skips peases of texts for the best speed. It stops only on [small set of chars](https://github.com/markdown-it/markdown-it/blob/master/lib/rules_inline/text.js), which can be tokens. We did not made this list extendable, also for performance reasons.

If you are absolutely sure, that something important is missed there - create a
ticket and we will consider adding new charcodes.


#### Why do you reject some useful things?

We do markdown parser. It should keep "markdown spirit". Other things should
be kept separate (in plugins, for example). We have no clear criteria, sorry.
Probably, you will find useful to read [CommonMark forum](http://talk.commonmark.org/) to understand us better.

Of cause, if you find architecture of this parser interesting for another type
of markup - you are welcome to reuse it in another project.