code: func IsInternal(file string) bool {
  	// fs cannot import config, so we hard code .stfolder here (config.DefaultMarkerName)
  	internals := []string{".stfolder", ".stignore", ".stversions"}
  	for _, internal := range internals {
  		if file == internal {
  			return true
  		}
  		if IsParent(file, internal) {
  			return true
  		}
  	}
  	return false
  }
docs: // IsInternal returns true if the file, as a path relative to the folder
  // root, represents an internal file that should always be ignored. The file
  // path must be clean (i.e., in canonical shortest form).