title: How to specify that at least one checkbox must be selected?
body: <p>I would like to use a <code>DataAnnotation</code> <code>Attribute</code> that tells the user that he must select one checkbox of the two following checkbox groups. My model is:</p>
  
  <pre><code>//group T
  public bool T0 {get;set;}
  public bool T1 {get;set;}
  public bool T2 {get;set;}
   //group P
  public bool P0 {get;set;}
  public bool P1 {get;set;}
  </code></pre>
  
  <p>The user must select at least one of the <code>T</code> properties, and one of the <code>P</code> properties. IS there something that do that on some customized dataannotations or i need to create one from beggining?</p>
  
  <p>Thanks</p>