title: String escape into XML
body: <p>Is there any C# function which could be used to escape and un-escape a string, which could be used to fill in the content of an XML element?</p>
  
  <p>I am using VSTS 2008 + C# + .Net 3.0.</p>
  
  <p>EDIT 1: I am concatenating simple and short XML file and I do not use serialization, so I need to explicitly escape XML character by hand, for example, I need to put <code>a&lt;b</code> into <code>&lt;foo&gt;&lt;/foo&gt;</code>, so I need escape string <code>a&lt;b</code> and put it into element foo.</p>