Support for custom extension

[alibell]

Context

The MyST-NB tool rely on MyST parser and support some pre-defined extensions. The markdown-it-py parser let it possible for user to create custom extensions, MyST inherit from this possibility using the use method.

In a current work, I developed some custom markdown extension for generating tables and figures for a data science report which rely on the Jupyter Book library.

My main issue is that I cannot declare my extension in Sphinx which rely on MyST-NB. I actually from with a kind of dirty fork of MyST-NB which load my custom extension directly in the parser.py file.

Proposal

• Let the user declare custom extension in the myst_enable_extensions parameter.
• Each custom extension should be named as: package.extension_name
• The parser should dynamically import the package and incorporate the extension named extension_name

Tasks and updates

No response

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[chrisjsewell]

Heya, I would be hesitant to tie myst-parser/myst-nb to markdown-it-py: the use of markdown-it-py is a design implementation that could change in the future and, as such, is not exposed to the user.

More generally, I would prefer to ultimately allow for the user just to provide the actual parser. The parser would be "loaded" with the configuration, then convert a source text to a JSON AST in a specified format (this is essentially what happens now). Then the myst-parser render would handle converting that JSON to the docutils/sphinx doctree.

Note, its normally more difficult than this though, to add a markdown-it extension, because there usually also has to be some logic added to themyst-parser renderer, to handle the new tokens created.