anchor.diff:  //    <ZWJ>    U+200D   ZERO WIDTH JOINER	      IdentifierPart
   fragment
   IdentifierPart
  -: UnicodeIDContinue
  -| [$_\u200C\u200D]
  -| '\\' UnicodeEscapeSequence
  +: (UnicodeIDContinue|[$_\u200C\u200D]|'\\' UnicodeEscapeSequence)
   ;
   
   // UnicodeIDStart::
  
positive.code: //    '\' UnicodeEscapeSequence
  fragment
  IdentifierStart
  : UnicodeIDStart
  | [$_]
  | '\\' UnicodeEscapeSequence
  ;
  
  // IdentifierPart::
  
negative.code: /* Source: ECMAScript® 2018 Language Specification - Annex A-1 */
  
  lexer grammar IdentifierName;
  
  // IdentifierName::
  //    IdentifierStart
  