code: func IsAlphanumeric(s string) bool {
  	for _, v := range s {
  		if ('Z' < v || v < 'A') && ('z' < v || v < 'a') && ('9' < v || v < '0') {
  			return false
  		}
  	}
  	return true
  }
docs: // IsAlphanumeric check if the string contains only letters and numbers. Empty string is valid.