How to add child element to XElement as a decoded string?
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I want to make pass this test. What should I use instead of Add method?

            [TestMethod]
            public void AddContentWithoutEncoding()
            {
                var element = new XElement("Parent");
    
                element.Add("<Sone>5</Sone>");
    
                Assert.IsTrue(element.ToString() == "<Parent><Sone>5</Sone></Parent>");
            }

With the current approach `element.ToString() = "<Parent>&lt;Sone&gt;5&lt;/Sone&gt;</Parent>"` that's obviously  encoding tag content.

I have a big constant string with tags which I need to add to XElement (because I use it feurther). And want to use some clever solution than `HttpUtility.HtmlDecode` - just add the decoded string rather than decode the whole result after adding.

Thanks!