XmlSerializer ignores [XmlAttribute] in WebApi

I have a WebApi that returns a simple object, but when I'm forcing it to return as XML (`Accept: application/xml`) it ignores the `[XmlAttribute]` attribute I've set on the object. This is my object: ``` public class Foo { [XmlAttribute] public string Bar { get; set; } } ``` And I return it like this in the code: ``` [RoutePrefix("api/mytest")] public class MyTestController : System.Web.Http.ApiController { [HttpGet] [Route("gettest")] public Foo GetTest() { return new Foo() { Bar = "foobar" }; } } ``` The resulting XML is: ``` <Foo> <Bar>foobar</Bar> </Foo> ``` Whereas I would expect it to be returned like this: ``` <Foo Bar="foobar"> </Foo> ``` Why does the XmlSerializer used by WebApi ignore the `[XmlAttribute]` attribute, and how can I make it work like I want to?