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)
