docs: function createErrorHandler(opts, transform) {
    return err => {
      if ('emit' === opts.error) {
        transform.emit('error', err)
      }
      else if ('function' === typeof opts.error) {
        opts.error(err)
      }
      else {
        const message = colors.red(err.name) + '\n' + err.toString()
          .replace(/(ParseError.*)/, colors.red('$1'))
        log(message)
      }
  
      transform.emit('end')
  
      if (opts.callback) {
        opts.callback(through2())
      }
    }
  }