TermAcronymDefinitionAdditional NotesOther Related Terms

An "A-label" is the ASCII-Compatible Encoding form of an IDNA-valid string. It must be a complete label: IDNA is defined for labels, not for parts of them and not for complete domain names. This means, by definition, that every A-label will begin with the IDNA ACE prefix, "xn--", followed by a string that is a valid output of the Punycode algorithm [RFC3492] and hence a maximum of 59 ASCII characters in length. The prefix and string together must conform to all requirements for a label that can be stored in the DNS including conformance to the rules for LDH labels. If and only if a string meeting the above requirements can be decoded into a U-label is it an A-label.

As defined in RFC 5890


Code Point    
Code Point Repertoire    
Cross-Script Variant Code Points 

Variant code points across related scripts, e.g. U+0441 CYRILLIC SMALL LETTER ES 'c' and U+0063 LATIN SMALL LETTER C 'c'

Internationalized Domain NameIDN

An "internationalized domain name" (IDN) is a domain name that contains at least one A-label or U-label, but that otherwise may contain any mixture of NR-LDH labels, A-labels, or U-labels.

As defined in RFC 5890A-Label, U-Label
Internationalized Domain Names in Applications Protocol 2003IDNA 2003   
Internationalized Domain Names in Applications Protocol 2008IDNA 2008   
Internationalized Domain Name LabelIDN Label   
Label: Allocatable    
Label: Allocated    
Label: Blocked    
Label: Reserved    
Label: Delegated    
Label: Activated    
Label Generation Ruleset / Label Generation RulesLGR   
LGR Specification    
Maximal Starting RepertoireMSR   
Variant "Variant" is an ambiguous term, as it can refer to Variant Code Point or Variant Label, and therefore it should be further qualified whenever it is used.  
Variant Code Point    
Variant Code Point Type    
Variant Label    
Variant Label Disposition    
Whole Label Evaluation RuleWLE Rule   
Writing System