Label Generation Rulesets

A Label Generation Ruleset (LGR) defines which characters may be used in a domain name for a given script or language, and which labels are considered variants of one another. Registries use them to decide what may be registered in a zone, and to identify the labels that must be withheld or reserved alongside a registration.
Rulesets are published as XML in the format defined by RFC 7940. Each one can be downloaded for use in software, or inspected interactively.
The rules determining which labels may be used as internationalised top-level domains in the DNS root zone, and which labels are variants of one another. Each script is maintained as its own element ruleset; the Common ruleset integrates them all.
Reference rulesets a registry can adopt as the basis of its own second-level policy. These are templates rather than operational rules: each carries instructions for adapting it to a zone and depositing the result in the IANA Repository of IDN Practices.
The rulesets and legacy tables deposited by top-level domain registries, describing the policies actually in force in their zones.
The IANA functions coordinate the Internet’s globally unique identifiers, and are provided by Public Technical Identifiers, an affiliate of ICANN.