Anchored Headings for Portable Text

Wondering how we would do something similar to this...

https://www.sanity.io/schemas/anchored-headings-for-portable-text-a6c70b6e - created by @kmelve

I think I understand how to create the new block definitions for h1, h2 etc..., or a complete handler like in the example above, but in the code below, I don't believe node is available from props? And I'm not sure what to return instead of return PortableText.defaultSerializers.types.block(props) (since defaultSerializers is no longer on PortableText)

const components: PortableTextComponents = {
  block: props => {
    const { node, children } = props
    const { style, _key } = node

    if (/^h\d/.test(style)) {
      const HeadingTag = style
      // Even though HTML5 allows id to start with a digit, we append it with a letter to avoid various JS methods to act up and make problems
      const headingId = `h${_key}`
      return (
        <HeadingTag id={headingId}>
          <a href={`#${headingId}`} aria-hidden="true" tabIndex={-1}>
            #
          </a>
          <span>{children}</span>
        </HeadingTag>
      )
    }
    // ... you can put in other overrides here

    // or return the default ones 👇
    return PortableText.defaultSerializers.types.block(props)
  }
}

Any thoughts or suggestions greatly appreciated.

Start with the linked Sanity anchored-headings example and the PortableTextComponents block callback shown in the issue. Determine how heading block data and the default block renderer are supported in the current API; done means a documented or implemented path that preserves default rendering while adding anchored headings.