EBNF is a family of metasyntax notations used to express context-free grammars: that is, a formal way to describe computer programming languages and other formal languages. They are extensions of the basic Backus–Naur Form (BNF) metasyntax notation.

The earliest EBNF was originally developed by Niklaus Wirth. However, many variants of EBNF are in use.

   digit excluding zero = "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;
   digit                = "0" | digit excluding zero ;