code: func toLowerASCII(s string) string {
  	var b []byte
  	for i := 0; i < len(s); i++ {
  		if c := s[i]; 'A' <= c && c <= 'Z' {
  			if b == nil {
  				b = make([]byte, len(s))
  				copy(b, s)
  			}
  			b[i] = s[i] + ('a' - 'A')
  		}
  	}
  
  	if b == nil {
  		return s
  	}
  
  	return string(b)
  }
docs: // toLowerASCII returns s with all ASCII capital letters lowercased.