Metasyntax
In logic and computer science, a metasyntax 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. 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). These metalanguages have their own metasyntax each composed of terminal symbols, nonterminal symbols, 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 languages") 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 languages) that have terminals, nonterminals, and metasymbols in their metasyntax. Specific metasyntax conventions. Variations. The metasyntax convention of these formal metalanguages are not yet formalized. Many metasyntactic variations or extensions exist in the reference manual of various computer programming languages. One variation to the standard convention for denoting nonterminals and terminals is to remove metasymbols such as angle brackets and quotations and apply "font types" to the intended words. In Ada, for example, syntactic categories are denoted by applying lower case sans-serif font on the intended words or symbols. All terminal words or symbols , in Ada, consist of characters of code position between and (inclusive). The definition for each character set is referred to the International Standard described by ISO/IEC 10646:2003. In C and Java, syntactic categories are denoted using italic font while terminal symbols are denoted by gothic font. In J, its metasyntax does not apply metasymbols to describe J's syntax at all. Rather, all syntactic explanations are done in a metalanguage very similar to English called Dictionary, which is uniquely documented for J. Advantage of the extensions. The purpose of the new extensions is to provide a simpler and unambiguous  metasyntax. In terms of simplicity, BNF's metanotation definitely does not help to make the metasyntax easier-to-read as the open-end and close-end metasymbols appear too abundantly. In terms of ambiguity, BNF's metanotation generates unnecessary complexity when quotation marks, apostrophes, less-than signs or greater-than signs come to serve as terminal symbols, which they often do. The extended metasyntax utilizes properties such as case, font, and code position of characters to reduce unnecessary aforementioned complexity. Moreover, some metalanguages use fonted separator categories to incorporate metasyntactic features for layout conventions, which are not formally supported by  BNF.