Extended Backus-Naur Form

from The Free On-line Dictionary of Computing (8 July 2008)

Extended Backus-Naur Form
Extended BNF

   <language> Any variation on the basic {Backus-Naur Form} (BNF)
   {meta-syntax} notation with (some of) the following additional
   constructs: {square brackets} "[..]" surrounding optional
   items, suffix "*" for {Kleene closure} (a sequence of zero or
   more of an item), suffix "+" for one or more of an item,
   {curly brackets} enclosing a list of alternatives, and
   super/subscripts indicating between n and m occurrences.

   All these constructs can be expressed in plain BNF using extra
   {productions} and have been added for readability and
   succinctness.

   (1995-04-28)