IRI

An Internationalized Resource Identifier (IRI) is a standard for identifying resources on the Internet using a broader range of characters than the traditional ASCII-based URI. IRIs enable Unicode characters from the Unicode standard to appear in web addresses and other identifiers, supporting non-Latin scripts and specialized symbols.

IRIs follow the same general syntax as URIs but permit Unicode characters in most components, including the path, query, and fragment. In practice, an IRI is typically mapped to an ASCII URI for transmission by applying percent-encoding to non-ASCII characters and using IDNA encoding for non-ASCII domain labels. This mapping allows existing protocols and systems that require ASCII to interoperate with Unicode-based identifiers.

Standards and mapping: The IRI specification is defined by RFC 3987 and related documents. It describes how IRIs are formed, compared, normalized, and mapped to URIs, as well as considerations for equivalence, security, and interoperability across protocols and platforms.

Usage and considerations: Major web browsers and many Internet protocols support IRIs, enabling users to enter non-ASCII web addresses directly. Implementations typically handle IRI-to-URI conversion automatically. Because DNS relies on ASCII, domain parts are commonly translated to ASCII via IDNA (often employing Punycode), while non-ASCII characters in paths, queries, and fragments are percent-encoded. Security considerations include homograph issues and normalization behavior, which can affect validation and comparison of identifiers.

See also: URI, URL, URN, IDNA, RFC 3987.