anchor.diff:  WITH:       'with' ;
   YIELD:      'yield' ;
   
  +// ref. Section 11.6.2.2
  +// FutureReservedWord::
  +//     enum
  +FUTURE_RESERVED_WORD
  +: ENUM
  +;
  +
  +ENUM: 'enum' ;
  +
  +// ref. Section 11.8.1
  +// NullLiteral::
  +//     null
  +NULL_LITERAL
  +: 'null'
  +;
  +
  +// ref. Section 11.8.2
  +// BooleanLiteral::
  +//     true
  +//     false
  +BOOLEAN_LITERAL
  +: 'true'
  +| 'false'
  +;
  +
   // ref. section 11.8.4
   // UnicodeEscapeSequence::
   //     'u' Hex4Digits
  
positive.code: | [\uDB40][\uDD00-\uDDEF]
  ;
  
  // ref. Section 11.6.2.1
  // Keyword::
  //     await
  
negative.code: //     var void
  //     while with
  //     yield
  KEYWORD
  : AWAIT
  | BREAK
  | CASE | CATCH | CLASS | CONST | CONTINUE
  | DEBUGGER | DEFAULT | DELETE | DO
  | ELSE | EXPORT | EXTENDS
  | FINALLY | FOR | FUNCTION
  | IF | IMPORT | IN | INSTANCEOF
  | NEW
  | RETURN
  | SUPER | SWITCH
  | THIS | THROW | TRY | TYPEOF
  | VAR | VOID
  | WHILE | WITH
  | YIELD
  ;
  
  AWAIT:      'await' ;
  BREAK:      'break' ;
  CASE:       'case' ;
  