function rehypePaperEmoji() {
  function transform(node) {
    if (node.tagName === 'img' && node.properties.dataEmojiCh) {
      return { type: 'text', value: node.properties.dataEmojiCh };
    }
    node.children = node.children ? node.children.map(transform) : node.children;
    return node;
  }

  return transform;
}
Dropbox Paper outputs emoji characters as images, and stores the actual
emoji character in a `data-emoji-ch` attribute on the image. This plugin
replaces the images with the emoji characters.