title: Need to remove illegal characters in XML string
body: <p>I have to process xml data in C#, however, sometimes there is an illegal XML character present.
  For example this XML code will not parse as it is invalid:</p>
  
  <pre><code>&lt;xml&gt;Another way to write a heart is &lt;3&lt;/xml&gt;
  </code></pre>
  
  <p>The XML parser will throw an error because it is not valid, which makes sense.
  Although, I don't seem to find a way to replace that only one "&lt;" to "&amp; lt;" so that the parser will receive:</p>
  
  <pre><code>&lt;xml&gt;Another way to write a heart is &amp;lt;3&lt;/xml&gt;
  </code></pre>
  
  <p>Footnote: it can occure in any node in the xml which can be pretty large itself and like I said before, it happens not all the time...</p>
  
  <p>Is there a function tthat can handle this?</p>