anchor.diff:      Expression expression = parsePrimaryExpression("'''string'''");
       expect(expression, isNotNull);
       assertNoErrors();
  -    expect(expression, new isInstanceOf<SimpleStringLiteral>());
  -    SimpleStringLiteral literal = expression;
  +    var literal = expression as SimpleStringLiteral;
       expect(literal.isMultiline, isTrue);
       expect(literal.isRaw, isFalse);
       expect(literal.value, "string");
  
positive.code:     Expression expression = parseThrowExpression('throw x');
      expect(expression, isNotNull);
      assertNoErrors();
      expect(expression, new isInstanceOf<ThrowExpression>());
      ThrowExpression throwExpression = expression;
      expect(throwExpression.throwKeyword, isNotNull);
      expect(throwExpression.expression, isNotNull);
    }
  
negative.code:     Expression expression = parseCascadeSection('..a<E>(b).c<F>(d)');
      expect(expression, isNotNull);
      assertNoErrors();
      var section = expression as MethodInvocation;
      expect(section.target, new isInstanceOf<MethodInvocation>());
      expect(section.operator, isNotNull);
      expect(section.methodName, isNotNull);
  