title: Control the setting of $viewValue in a directive's nested ngModel
body: <p>I have a fairly simple UI control that I've modeled as a directive, which is an editor for phone numbers that has two input fields: one for the country code and another for the number.</p>
  
  <p>The directive's usage looks like this:</p>
  
  <pre><code>&lt;phone-editor ng-model='phoneNo'&gt;&lt;/phone-editor&gt;
  </code></pre>
  
  <p>In the directive's declaration, I require ngModel and the template looks like this:</p>
  
  <pre><code>&lt;input type="text" ng-model="countryCode" /&gt;
  &lt;input type="text" ng-model="number" /&gt;
  </code></pre>
  
  <p>It's clear how to compose and decompose the original model into the two fields.</p>
  
  <p>What I cannot figure out is - how do I use a formatter for the second field such that it displays <code>(555) 555-5555</code> instead of the plain number, without defining another directive just to access the ngModel controller of the second input field?</p>
  
  <p>Can I somehow access the child ngModel controller?</p>