Extended Backus-Naur form

The Extended Backus-Naur form (EBNF) is any variation on the basic Backus-Naur form (BNF) metasyntax 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, suffix for zero or one of an item, Bracket {..} enclosing a list of alternatives,

super/subscripts indicating between n and m occurrences.

When Niklaus Wirth was developing Pascal programming language, he simplified Backus-Naur Form to create EBNF.

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

There is an International standard ([http://www.iso.org/iso/en/CatalogueDetailPage.CatalogueDetailCSNUMBER=26153 ISO 14977]) that defines an EBNF. A draft is freely available from http://www.cl.cam.ac.uk/~mgk25/iso-ebnf.html. Please note that this draft document has some mistakes in it. Throughout the text, as well as in the comments of the examples, `meta-identifiers are `written as one or more words joined together by hyphens (as stated in section 4). On the other hand, all examples (except the comments) use spaces to separate several words.

The syntax.

=See also=

Spirit Parser Framework

=References=

=External links=

*Article [http://www.garshol.priv.no/download/text/bnf.html BNF and EBNF: What are they and how do they work] by Lars Marius Garshol *Article [http://xml.com/pub/a/2001/07/25/namingparts.html The Naming of Parts] by John E. Simpson *[http://www.cl.cam.ac.uk/~mgk25/iso-14977.pdf ISO/IEC 14977 : 1996(E)] *[http://citeseer.ist.psu.edu/cisq=Extended+Backus+Naur+Form Citations from CiteSeer]