<ebnf> “Backus-Naur Form” {

syntax         = rule [ syntax ] .
rule           = opt-ws  identifier opt-ws "::=" opt-ws expression opt-ws EOL .
expression     = list [ "|" expression ] .
line-end       = opt-ws EOL | line-end line-end .
list           = term [ WHITESPACE list ] .
term           = literal | identifier .
identifier     = "<" character {character} ">" .
literal        = "'" {character} "'" | '"'  {character} '"' .
opt-ws         = { WHITESPACE } .
character      = lowercase-char | uppercase-char | digit | special-char .
lowercase-char = "a" | "b" | "..." | "z" .
uppercase-char = "A" | "B" | "..." | "Z" .
digit          = "0" | "1" | "..." | "2" .
special-char   = "-" | "_" .

} </ebnf>