title: select at least one checkbox out of 3 required field validator
body: <p>I am trying to make my code to put required field validator so at least one checkbox will be selected out of three. 
  This is my code:</p>
  
  <pre><code>&lt;div class="left marginT5 marginR10"&gt;
   &lt;input type="checkbox" id="chk1" value="option1" runat="server" class="styled" /&gt; Choice1
   &lt;/div&gt;
   &lt;div class="left marginT5 marginR10"&gt;
  &lt;input type="checkbox" id="chk2" value="option2" runat="server" class="styled" /&gt; Choice2
   &lt;/div&gt;
   &lt;div class="left marginT5 marginR10"&gt;
   &lt;input type="checkbox" id="chk3" value="option3" runat="server" class="styled" /&gt; Choice3
   &lt;/div&gt;
  </code></pre>
  
  <p>I know I can use checkboxlist but because of design issues I can only use single checkbox controls. 
  Any idea how I can "force" the user to select at least one checkbox?
  Thanks in advance, Laziale</p>