Pass heading classes via Goldmark to render-heading hook

[peaceiris]

This previous work may be helpful.

A way to add parameters to image and link render hooks

While there’s a proposal to add parameters to render hooks, I found a somewhat decent solution which uses the title attribute and the transform.Unmarshal function. Links and images in markdown allow you to specify a title parameter.  [Link text](url 'title') Using the transform.Unmarshal function, we can set the title to a JSON string which can then make the parameters. For example, here’s how you can use the title to add additional attributes to the rendered link tag…