Notation for production rules in EBNF

A ::= x y z concatenation xyz A ::= x1|x2|...|xk alternative x1 or x2 A ::= x [y] z option xz or xyz A ::= x {y} z repetition xz or xyz or xy or yz A ::= x {y}+ z repetition y at least once (xz is forbidden) A ::= (a | x) (b | z) bracketing of text parts ab or xb or az or xz