code: function remark2rehype(destination, options) {
    if (destination && !destination.process) {
      options = destination
      destination = null
    }
  
    return destination ? bridge(destination, options) : mutate(options)
  }
docs: Attacher.  If a destination is given, runs the destination with the new hast tree (bridge-mode).   Without destination, returns the hast tree: further plugins run on that tree (mutate-mode).