react-spring/docs/scripts/mdx/rehype-highlight-word.js

/**
 * Credit to https://ped.ro/writing/code-blocks-but-better
 */

import { toHtml } from 'hast-util-to-html'
import { unified } from 'unified'
import parse from 'rehype-parse'

const CALLOUT = /__(.*?)__/g

export default function (code) {
  const html = toHtml(code)
  const result = html.replace(
    CALLOUT,
    (_, text) => `<span class="highlight-word">${text}</span>`
  )
  const hast = unified()
    .use(parse, { emitParseErrors: true, fragment: true })
    .parse(result)
  return hast.children
}