(* Grammatical EBNF *)
Ruleset     = (COMMENT? Rule)* EOI ;
Rule        = ident '=' Either? ';' ;
Either      = Follow ('|' Follow)* ;
Follow      = (Any | Many | Maybe | Not)+ ;
Any         = Not '*' ;
Many        = Not '+' ;
Maybe       = Not '?' ;
Not         = '!'? Prime ;
Prime       = Group | chr | str | ident ;
Group       = '(' Either ')' ;

ident       = XID_START XID_CONTINUE* ;
str         = '"' (!'"' ANY)* '"' ;
chr         = "'" (!"'" ANY)* "'" ;

WHITESPACE  = WHITE_SPACE ;
COMMENT     = "(*" (COMMENT | !"*)" ANY)* "*)" ;