anchor.diff:  TOK_WS
      : Ws+ -> type (WS) , channel (OFF_CHANNEL)
      ;
  -   // -------------------------
  -
  +
  +// -------------------------
   mode Channels;
   // currently same as Tokens mode; distinguished by keyword
   CHN_DOC_COMMENT
  
positive.code: // parser. This means that the parser to deal with the gramamr file anyway
  // but we will not try to analyse or code generate from a file with lexical
  // errors.
  //
  // Comment this rule out to allow the error to be propagated to the parser
  // ERRCHAR
  //    : . -> channel (HIDDEN)
  //    ;
  
  // ======================================================
  // Lexer modes
  
negative.code:    { handleEndArgument(); }
     ;
  
  // added this to return non-EOF token type here. EOF does something weird
  UNTERMINATED_ARGUMENT
     : EOF -> popMode
     ;
  