How to implement custom markdown-it-py render to default Jupyter Notebook behavior?

[Pandaski]

I cannot raise a question in markdown-it-py so I put my question here, hope here is the right place.

I am new for JupyterBook/MyST/markdown-it-py. Currently I am able to create a custom markdown-it-py render by following the demo code at render. However I don't know how to make this custom render to jupyter notebook default behavior. i.e. I can get the expected rendered HTML (an iframe as the demo code implemented) by running below in a python cell

print(md.render("![](https://www.vimeo.com/123)"))

However, in a normal markdown cell, the same markdown code is still rendered as an image

![](https://www.vimeo.com/123)

I have installed jupytext, myst-nb, jupyterlab-myst, and started my jupyterlab as an editor tool. My goal is to add a custom markdown syntax to my owned jupyter notebook server (no plan to publish it before I fully understand the MyST).

Any suggestion is welcome and thanks in advance.