title: WebApi force action to return xml
body: <p>I have this action:</p>
  
  <pre><code>public IHttpActionResult SearchFor(int aboItemType, DTO.FilterColumns filter)
  {
      //Do stuff...
      return Ok&lt;DataSet&gt;(ds);
  }
  </code></pre>
  
  <p>My client does:</p>
  
  <pre><code>client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/xml"));
  
  var response = client.PostAsJsonAsync(myurl).Result;
  if (response.IsSuccessStatusCode)
  {
      var results = HttpUtility.HtmlDecode(response.Content.ReadAsStringAsync().Result);
  }
  </code></pre>
  
  <p>The above scenario works perfectly. However, if I comment the Accept line, the action returns the dataset in json format. </p>
  
  <p>I would like to force this one particular action to always send the result in xml. Is this possible? Maybe with an attribute?</p>