{version 2022-05-19}
         ixml: s, prolog?, rule++RS, s.

       prolog: version, s.
      version: -"ixml", RS, -"version", RS, -string, s, -'.' .

           -s: (whitespace; comment)*. {Optional spacing}
          -RS: (whitespace; comment)+. {Required spacing}
  -whitespace: -[Zs]; tab; lf; cr.
         -tab: -#9.
          -lf: -#a.
          -cr: -#d.
      comment: -"{", (cchar; comment)*, -"}".
       -cchar: ~["{}"].

         rule: (mark, s)?, name, s, -["=:"], s, -alts, -".".
        @mark: ["@^-"].
         alts: alt++(-[";|"], s).
          alt: term**(-",", s).
        -term: factor;
               option;
               repeat0;
               repeat1.
      -factor: terminal;
               nonterminal;
               -"(", s, alts, -")", s.
      repeat0: factor, (-"*", s; -"**", s, sep).
      repeat1: factor, (-"+", s; -"++", s, sep).
       option: factor, -"?", s.
          sep: factor.
  nonterminal: (mark, s)?, name, s.

        @name: namestart, namefollower*.
   -namestart: ["_"; L].
-namefollower: namestart; ["-.·‿⁀"; Nd; Mn].

    -terminal: literal; 
               charset.
      literal: quoted;
               encoded.
      -quoted: (tmark, s)?, string, s.

       @tmark: ["^-+"].
      @string: -'"', dchar+, -'"';
               -"'", schar+, -"'".
       -dchar: ~['"'; #a; #d];
               '"', -'"'. {all characters except line breaks; quotes must be doubled}
       -schar: ~["'"; #a; #d];
               "'", -"'". {all characters except line breaks; quotes must be doubled}
     -encoded: (tmark, s)?, -"#", hex, s.
         @hex: ["0"-"9"; "a"-"f"; "A"-"F"]+.

     -charset: inclusion; 
               exclusion.
    inclusion: (tmark, s)?,          set.
    exclusion: (tmark, s)?, -"~", s, set.
         -set: -"[", s,  (member, s)**(-[";|"], s), -"]", s.
       member: string;
               -"#", hex;
               range;
               class.
       -range: from, s, -"-", s, to.
        @from: character.
          @to: character.
   -character: -'"', dchar, -'"';
               -"'", schar, -"'";
               "#", hex.
       -class: code.
        @code: capital, letter?.
     -capital: ["A"-"Z"].
      -letter: ["a"-"z"].