Extending Internationalised Domain Names in Applications to Other Protocols (X-IDNA)
Prior to Internationalised Domain Names in Applications (IDNA), there has been no standard method for domains, names, addresses and similar identifiers to use characters outside the ASCII repertoire. This still applies to many identifiers that are no domain names, such as email addresses (local-part), newsgroup names, etc. This document extends the mechanism defined in IDNA to other protocols and their identifiers. As with IDNA, these identifiers may be drawn from a large repertoire (Unicode) and are mapped to backward-compatible identifiers using only ASCII characters. For valid domain names, X-IDNA produces the same encoding as IDNA, even when these domain names are embedded in other addresses.