title: An invalid form control with name='' is not focusable on hidden element
body: <p>I have an element that conditionally appears that is required to be filled out when visible. (using ng-required)</p>
  
  <p>However, when it is not visible, I'm getting the following error:</p>
  
  <blockquote>
    <p>An invalid form control with name='' is not focusable</p>
  </blockquote>
  
  <p>How do I force ng-required to work ONLY if it element is visible.  I do not want to enter novalidate in the form, because if I do, when the element is visible, the validation does not occur.</p>