anchor.diff:  // 2.3
   fragment Delimiter : Operator | Separator | Bracket | Declarator | Specificator ;
   fragment Operator : Arithmetic_operator | Relational_operator_f | Logical_operator | Sequential_operator ;
  -fragment Arithmetic_operator : Plus_ | Minus_ | Times_ | Divide_ | Exp_ ;
  +fragment Arithmetic_operator : Plus_ | Minus_ | Mult_ | Divide_ | Exp_ ;
   fragment Relational_operator_f : Lt_ | Le_ | Eq_ | Ne_ | Gt_ | Ge_ ;
   Relational_operator : Relational_operator_f ;
   fragment Logical_operator : Equiv_ | Includes_ | Or_ | And_ | Not_ ;
  
positive.code: Rb_ : ']' ;
  Rp_ : ')' ;
  Semi_ : ';' ;
  Times_ : '×' | '*' ;
  Underscore_ : '_' ;
  
  // 2.1
  
negative.code: number : Unsigned_number | Plus_ Unsigned_number | Minus_ Unsigned_number ;
  
  // 2.6.1
  fragment Proper_string : (~('\u231C' | '\u231D'))* ;
  fragment Open_string : Proper_string | Proper_string Closed_string Open_string ;
  fragment Closed_string : ULCorner Open_string URCorner ;
  fragment StdString : Closed_string | Closed_string StdString ;
  String : StdString // String according to spec.
     | '"' ~'"'* '"' | '`' ~'\''* '\'' ; // Additional non-standard strings used in examples.
  
  // 3
  expression : arithmetic_expression | boolean_expression | designational_expression ;
  