Question

Why can’t I call FirstOrDefault() on this XML, whereas I have other XDocuments where FirstOrDefault() is available?

        var actual = new XDocument(
            new XComment("This is a comment"),
            new XElement("Root",
                         new XElement("Child1", "data1"),
                         new XElement("Child2", "data2")
                ));

        actual.Descendants("Child1"). <- FirstOrDefault does not show up.

Answer 1

You should include System.Linq namespace in the top of your cs file.
If you’re using ReSharper, try push ctrl+alt+space after typing . and look for FirstOrDefault. R# helps to manage namespaces.