function createProcessor(options) {
  const rehypePlugins = options.rehypePlugins || emptyPlugins
  const remarkPlugins = options.remarkPlugins || emptyPlugins
  const remarkRehypeOptions = options.remarkRehypeOptions
    ? {...options.remarkRehypeOptions, ...emptyRemarkRehypeOptions}
    : emptyRemarkRehypeOptions

  const processor = unified()
    .use(remarkParse)
    .use(remarkPlugins)
    .use(remarkRehype, remarkRehypeOptions)
    .use(rehypePlugins)

  return processor
}
Set up the `unified` processor.

@param {Readonly<Options>} options
  Props.
@returns {Processor<MdastRoot, MdastRoot, Root, undefined, undefined>}
  Result.