code: func (s *scanner) Next() (rune, bool) {
  	if s.i >= len(s.s) {
  		return 0, false
  	}
  	r := s.s[s.i]
  	s.i++
  	return r, true
  }
docs: // Next returns the next rune.
  // It returns 0, false if the end of the text has been reached.