Editing Metasyntax (section)

{{Short description|Allowable structure and composition of phrases and sentences of a metalanguage}}
{{More citations needed|date=December 2009}}

A '''metasyntax''' is a syntax used to define the syntax of a [[programming language]] or [[formal language]]. It describes the allowable structure and composition of phrases and sentences of a [[metalanguage]], which is used to describe either a [[natural language]] or a computer programming language.<ref>Sellink, Alex, and Chris Verhoef. "[http://ai2-s2-pdfs.s3.amazonaws.com/575f/904555f4b6eb7d89ab84e2f4e4ca677ce17b.pdf Development, assessment, and reengineering of language descriptions]." Software Maintenance and Reengineering, 2000. Proceedings of the Fourth European. IEEE, 2000.</ref> Some of the widely used formal metalanguages for computer languages are [[Backus–Naur form]] (BNF), [[extended Backus–Naur form]] (EBNF), [[Wirth syntax notation]] (WSN), and [[augmented Backus–Naur form]] (ABNF).

Metalanguages have their own metasyntax each composed of [[terminal symbol]]s, [[nonterminal symbol]]s, and ''metasymbols''. A terminal symbol, such as a word or a token, is a stand-alone structure in a language being defined. A nonterminal symbol represents a [[syntactic]] category, which defines one or more valid phrasal or sentence structure consisted of an n-element subset. Metasymbols provide syntactic information for denotational purposes in a given metasyntax. Terminals, nonterminals, and metasymbols do not apply across all metalanguages.

Typically, the metalanguage for token-level languages (formally called "[[regular language]]s") does not have nonterminals because nesting is not an issue in these regular languages. English, as a metalanguage for describing certain languages, does not contain metasymbols since all explanation could be done using English expression. There are only certain formal metalanguages used for describing recursive languages (formally called [[context-free language]]s) that have terminals, nonterminals, and metasymbols in their metasyntax.