смотри BNF= Backus Normal Form
(BNF, originally "Backus Normal Form") A formal metasyntax used to express context-free grammars. Backus Normal Form was renamed Backus-Naur Form at the suggestion of Donald Knuth. BNF is one of the most commonly used metasyntactic notations for specifying the syntax of programming languages, command sets, and the like. It is widely used for language descriptions but seldom documented anywhere, so that it must usually be learned by osmosis (but see RFC 2234). There are many variants and extensions of BNF, possibly containing some or all of the regexp wild cards such as "*" or "+". EBNF is a common one. In fact the example above isn't the pure form invented for the ALGOL 60 report. "" was introduced a few years later in IBM's PL/I definition but is now universally recognised. ABNF is another extension.