BNF (Backus-Naur Form)
A way of formally describing the grammar of a language or set of commands. Each
element in the language is described in terms of its component elements, which in
turn are described by their components. There can be mandatory, optional or repeating
elements. Definitions of terms can be recursive. The term BNF
is loosely used to describe any scheme for describing a grammar from Burroughs
railway diagrams to LALR (Look Ahead Left-to-Right parse) though properly it refers to Backus’s original.
It is useful mainly for language lawyers. People understand a grammar best from a
carefully chosen set of examples.