VS 2013 Code Analysis rule 2000 for disposing object not generating error for XMlNodeList

default rule "Rule CA2000: Dispose objects before loosing scope", reports error is object is not disposed

below code shows error as expected, as SqlConnection is not disposed

SqlConnection con = new SqlConnection();

But same rule doesn't show error for XmlNodeList class, as shown below

XmlDocumemt doc = new XmlDocument();

XmlNodeList nodeList = doc.GetElementsByTagName("tag");

why rule is not showing error for XMlNodeList (I am using VS 2013)?

Thanks

singhhome