IDNA (Internationalized Domain Names in Applications)
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IDNA is the technical framework defining how [[idn|internationalized domain names]] are processed in applications and protocols. The current standard, IDNA 2008 (RFC 5891–5894), specifies how Unicode labels are validated, normalized, and converted to [[punycode|Punycode]] ACE form (xn--). IDNA 2008 tightened rules compared to its predecessor, restricting characters like hyphens and symbols that IDNA 2003 permitted, improving consistency across different languages and scripts.
Example
IDNA 2008 rejects the emoji domain '🍕.com' (allowed by IDNA 2003) because emoji are not valid IDNA 2008 label characters, causing browser compatibility inconsistencies.