title: MVC3 Input Dependent Validation
body: <p>Note: I'm relatively new to MVC3.<br>
  Input validation seems to be pretty nice with this framework, where you can just say [Required] and both client and server side validation just works from there.  But what if I would like to implement conditional validation?</p>
  
  <p>Scenario: I will have a dropbox box that requires you to choose one of 2 options.  If option 1 is selected, 2 text input fields will appear and both are required.  If option 2 is selected, 2 radio buttons will appear and you are required to select one of them.  How can MVC3 validation achieve this?</p>
  
  <p>Obviously, in the Model we can't have just standard required validation, as some fields won't be submitted depending on which drop-down option we choose. </p>