code: func (fs *FS) NewRequestHandler() RequestHandler {
  	fs.once.Do(fs.initRequestHandler)
  	return fs.h
  }
docs: // NewRequestHandler returns new request handler with the given FS settings.
  //
  // The returned handler caches requested file handles
  // for FS.CacheDuration.
  // Make sure your program has enough 'max open files' limit aka
  // 'ulimit -n' if FS.Root folder contains many files.
  //
  // Do not create multiple request handlers from a single FS instance -
  // just reuse a single request handler.