EBNF
Even EBNF can be described using EBNF. Consider the sketched grammar below:
1 letter = "A" | "B" | "C" | "D" | "E" | "F" | "G"
2 | "H" | "I" | "J" | "K" | "L" | "M" | "N"
3 | "O" | "P" | "Q" | "R" | "S" | "T" | "U"
4 | "V" | "W" | "X" | "Y" | "Z" | "a" | "b"
5 | "c" | "d" | "e" | "f" | "g" | "h" | "i"
6 | "j" | "k" | "l" | "m" | "n" | "o" | "p"
7 | "q" | "r" | "s" | "t" | "u" | "v" | "w"
8 | "x" | "y" | "z" ;
9 digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;
10 symbol = "[" | "]" | "{" | "}" | "(" | ")" | "<" | ">"
11 | "'" | '"' | "=" | "|" | "." | "," | ";" ;
12 character = letter | digit | symbol | "_" ;
13
14 identifier = letter , { letter | digit | "_" } ;
15 terminal = "'" , character , { character } , "'"
16 | '"' , character , { character } , '"' ;
17
18 lhs = identifier ;
19 rhs = identifier
20 | terminal
21 | "[" , rhs , "]"
22 | "{" , rhs , "}"
23 | "(" , rhs , ")"
24 | rhs , "|" , rhs
25 | rhs , "," , rhs ;
26
27 rule = lhs , "=" , rhs , ";" ;
28 grammar = { rule } ;