title: Choose input validation based on selection in dropdown
body: <p>I'm trying to setup validation on a field based on which option a user chooses from a dropdown. If they choose 'email' I run email validation on the input field. If they choose 'user' I run number validation on the field. I would like to use <code>ng-if</code> on each of these possible input fields and choose which one to show based on the value selected from the dropdown, but I can't seem to figure out how to best determine which option they chose. Current Jade code below:</p>
  
  <pre><code>td
    div.btn-group
      button.btn.btn-primary(data-toggle='dropdown' ng-model='type')#type Type
      button.btn.dropdown-toggle.btn-primary(data-toggle='dropdown')
        span.caret
      ul.dropdown-menu(role='menu')#list
        - for (var x in listTypes)
          li
            a(class='list-type' data-list-type-uri='#{x}' data-list-type='#{listTypes[x].name}')= listTypes[x].name
  td
    input.form-control(name='listType' id='list', type='text', placeholder='List Type' ng-model='email' validator='email' required message-id='email')
    span(id='email' ng-hide='!email.length')
    input.form-control(name='listType' id='list', type='text', placeholder='List Type' ng-model='user' validator='number' required message-id='number')
    span(id='number' ng-hide='!number.length')
  </code></pre>