title: How to encode the ampersand if it is not already encoded?
body: <p>I need a c# method to encode ampersands if they are not already encoded or part of another encoded epxression</p>
  
  <p>eg </p>
  
  <pre><code>"tom &amp; jill" should become "tom &amp;amp; jill"
  
  
  "tom &amp;amp; jill" should remain "tom &amp;amp; jill"
  
  
  "tom &amp;euro; jill" should remain "tom &amp;euro; jill"
  
  
  "tom &lt;&amp;&gt; jill" should become "tom &lt;&amp;amp;&gt; jill"
  
  
  "tom &amp;quot;&amp;&amp;quot; jill" should become "tom &amp;quot;&amp;amp;&amp;quot; jill"
  </code></pre>