code: func removeInvalidAtIndex(i int, runes []rune) []rune {
  	valid := i
  	for ; valid < len(runes) && !validIdentifier(runes[valid]); valid++ {
  	}
  
  	return append(runes[:i], runes[valid:]...)
  }
docs: // removeInvalidAtIndex removes consecutive invalid identifiers from runes starting at index i.