Internationalized resource identifier

The Internationalized Resource Identifier (IRI) was defined by the Internet Engineering Task Force (IETF) in 2005 as a new internet standard to extend upon the existing Uniform Resource Identifier (URI) scheme. The new standard was published in RFC 3987.

While URIs are limited to a subset of the ASCII character set, IRIs may contain characters from the Universal Character Set (Unicode/ISO 10646), including Chinese or Japanese kanji, Korean, Cyrillic characters, and so forth.

IRI extend upon URIs by using the Universal Character Set whereas URIs were limited to the ASCII with far fewer characters. IRIs may be represented by a sequence of octets but by definition is defined as a sequence of characters because IRIs can be spoken or written by hand.

IRIs are mapped to URIs to retain backwards-compatibility with systems that do not support the new format.

For applications and protocols that do not allow direct consumption of IRIs, the IRI should first be converted to Unicode using canonical composition normalization (NFC), if not already in Unicode format.

All non-ASCII code points in the IRI should next be encoded as UTF-8, and the resulting bytes percent-encoded, to produce a valid URI.

ASCII code points that are invalid URI characters may be encoded the same way, depending on implementation.

This conversion is easily reversible; by definition, converting an IRI to an URI and back again will yield an IRI that is semantically equivalent to the original IRI, even though it may differ in exact representation.

Some protocols may impose further transformations; e.g. Punycode for DNS labels.

There are reasons to see URIs displayed in different languages; mostly, it makes it easier for users who are unfamiliar with the Latin (A-Z) alphabet. Assuming that it isn't too difficult for anyone to replicate arbitrary Unicode on their keyboards, this can make the URI system more accessible.

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