code: func IsHostname(str string) bool {
  	if !rxHostname.MatchString(str) {
  		return false
  	}
  
  	// the sum of all label octets and label lengths is limited to 255.
  	if len(str) > 255 {
  		return false
  	}
  
  	// Each node has a label, which is zero to 63 octets in length
  	parts := strings.Split(str, ".")
  	valid := true
  	for _, p := range parts {
  		if len(p) > 63 {
  			valid = false
  		}
  	}
  	return valid
  }
docs: // IsHostname returns true when the string is a valid hostname