Technical limitations of IDNs

Internationalized domains (IDN) whose names contain diacritics or special characters have, in addition to the standard limitations, the following additional technical limitations:

• you cannot mix multiple character sets in the same domain name. For example, mixing Greek characters with Cyrillic characters in the same name is not allowed;
• a domain name cannot be longer than 63 characters once converted to ACE format
• a domain name cannot start with the characters xn--, which are reserved for the ACE format
• not all characters are allowed — for example, the German character ß is not allowed