# The EBNF syntax allowed by bnf_chk.

# A BNF file is a sequence of zero or more rules:
bnf_file = { rule };
rule = identifier "=" expression ";" ;
identifier = ( letter | "_" ) { letter | digit | "_"  } ;
letter = "a".."z" | "A".."Z" ;
digit = "0".."9" ;
expression = term { "|" term } ;
term = factor { factor } ;
factor = identifier | literal | range | "(" expression ")"
	| "{" expression "}" | "[" expression "]" ;
literal = "\"" { char } "\"" ;
range = "\"" char "\"" ".." "\"" char "\"" ;
char = plain_char | escaped_char | hex_char;
plain_char = "\x20".."\x7F" | "\x80".."\xFF" | utf_16_char;
escaped_char = "\\" ("\"" | "\\" | "a" | "b" | "n" | "r" | "t");
hex_char = "\\x" hex hex;
# UTF-16 chars supported only in the new stand-alone JavaScript implementation:
utf_16_char = "\\u" hex hex hex hex;
hex = "0".."9" | "a".."f" | "A".."F";