title: ngTagsInput: Validation while typing
body: <p>I have a field where I validate for email addresses using ngTagsInput. If the input is valid, then I want to enable a button, else disable that button.</p>
  
  <ul>
  <li>Say the text box contains, abc@abc.com -> Button is enabled </li>
  <li>Say the
  user is typing in the text box and the box contains, abc@abc.com aa
  -> Button should be disabled</li>
  <li>Say the user is typing in the text box and the box contains, abc@abc.com aa@aa.com
  -> Button should be enabled</li>
  </ul>
  
  <p>If the user does not have focus on the text box, I can validate using $error.leftoverText and using $invalid to determine if the text box contains valid emails</p>
  
  <p>However, if the user has focus on the text box, It seems that the $error.leftoverText does not exist, and the $invalid is actually false. Is there a way to use the ngTagsInput when the user has focus on the field and validate the email address?</p>