start: (_item | _NL)*

_item: rule
     | token
     | statement

rule: RULE priority? ":" expansions _NL
token: TOKEN priority? ":" expansions _NL

priority: "." NUMBER

statement: "%ignore" expansions _NL                -> ignore
         | "%import" import_args ["->" TOKEN] _NL  -> import

import_args: name ("." name)*

?expansions: alias (_VBAR alias)*

?alias: expansion ["->" RULE]

?expansion: expr*

?expr: atom [OP | "~" NUMBER [".." NUMBER]]

?atom: "(" expansions ")"
     | "[" expansions "]" -> maybe
     | STRING ".." STRING -> literal_range
     | name
     | (REGEXP | STRING) -> literal

name: RULE
    | TOKEN

_VBAR: _NL? "|"
OP: /[+*][?]?|[?](?![a-z])/
RULE: /!?[_?]?[a-z][_a-z0-9]*/
TOKEN: /_?[A-Z][_A-Z0-9]*/
STRING: _STRING "i"?
REGEXP: /\/(?!\/)(\\\/|\\\\|[^\/\n])*?\/[imslux]*/
_NL: /(\r?\n)+\s*/

%import common.ESCAPED_STRING -> _STRING
%import common.INT -> NUMBER
%import common.WS_INLINE

COMMENT: "//" /[^\n]/*

%ignore WS_INLINE
%ignore COMMENT