docs: private void error(String expected, String actual) {
          if (!recovering) {
              recovering = true;
              final String outputString = (EOF_STRING.equals(actual) || UNTERMINATED_COMMENT_STRING.equals(actual) || COMMENT_NOT_ALLOWED.equals(actual)) ? actual : "'"
                      + actual + "'";
              errors.add(SyntaxError._UnexpectedToken(expected, outputString,
                      lookahead(1).beginLine));
          }
      }