This Recommendation provides meta-grammars for ITU-T Recommendations that define ITU-T languages in the X.680-series and the Z-series Recommendations on languages for specification, implementation, modeling and testing. This allows the description of these meta-grammars that define the abstract or concrete grammar (syntax, constraints and semantics) of languages without having to repeat the meta-grammar (such as lexical naming rules, or the description of Backus-Naur Form syntax) as a preamble or annex to each language definition. The Recommendation draws common elements from the meta-grammars of variously languages, covering issues such as common lexical rules, the use of a universal character set, and syntax and constraint description for languages at both the abstract and concrete level.