Extended Backus-Naur form

Extended Backus-Naur form, abbreviated EBNF, is a family of metasyntax notations that can express a context-free grammar. It is used to give a formal description of a formal language such as a computer programming language, and it extends the basic Backus-Naur form metasyntax notation. An EBNF consists of terminal symbols and non-terminal production rules that restrict how terminal symbols may be combined into a valid sequence, and it adds notation for repetition, optional parts, exclusion and comments. The earliest EBNF was developed by Niklaus Wirth, drawing on concepts from his Wirth syntax notation, and many variants are in use today. The International Organization for Standardization adopted an EBNF standard, ISO/IEC 14977, in 1996, although a researcher quoted in the article observes that the standard added three more dialects rather than unifying the field.