The extensions to Backus-Naur Form that are used by the turbomachine NDF are listed below:
Optional items are enclosed in square brackets:
[<item-x>].Items repeating 0 or more times are enclosed in curly brackets or suffixed with an asterisk,
*, such as<word> ::= <letter> {<letter>}or<word> ::= <letter> <letter>*, respectively.Items repeating 1 or more times are suffixed with an addition (plus) symbol,
+.Alternative choices in a production are separated by the
|symbol:<alternative-A> | <alternative-B>.Where items are grouped, they are enclosed in simple parentheses,
().