anchor.diff:      assert(optional('export', token));
       Token exportKeyword = token;
       listener.beginExport(exportKeyword);
  -    token = ensureParseLiteralString(token.next);
  +    token = ensureParseLiteralString(token);
       token = parseConditionalUris(token.next);
       token = parseCombinators(token);
       token = ensureSemicolon(token);
  
positive.code:     Token throwToken = token;
      token = allowCascades
          ? parseExpression(token.next)
          : parseExpressionWithoutCascade(token.next);
      listener.handleThrowExpression(throwToken, token);
      return token;
    }
  
negative.code: 
      if (identical(token.type.precedence, ASSIGNMENT_PRECEDENCE)) {
        Token assignment = token;
        token = parseExpressionWithoutCascade(token);
        listener.handleAssignmentExpression(assignment);
      }
      listener.endCascade();
  