title: Why does $parent.$index equals $index?
body: <p>In AngularJS 1.6.3 it is basically possible to nest ng-repeat. </p>
  
  <p>I have determined, that in two nested ng-repeat the $parent.$index equals $index. </p>
  
  <p>The following code is given:</p>
  
  <pre><code>&lt;div ng-repeat="category in :: $ctrl.categories"&gt;
    &lt;span id="category-{{ $index }}"&gt;
      {{ :: category.name }}
    &lt;/span&gt;
  
    &lt;ul&gt;
     &lt;li ng-repeat="data in :: category.links"
         id="link-{{ $parent.$index }}-{{ $index }}"&gt;
       {{ :: data.name }}
     &lt;/li&gt;
    &lt;/ul&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p><strong>Expected</strong> resulting ID's for LI:</p>
  
  <pre><code>&lt;div&gt;
    &lt;span id="category-0"&gt;CatA&lt;/span&gt;
  
    &lt;ul&gt;
      &lt;li id="link-0-0"&gt;[..]&lt;/li&gt;
      &lt;li id="link-0-1"&gt;[..]&lt;/li&gt;
      &lt;li id="link-0-2"&gt;[..]&lt;/li&gt;
    &lt;/ul&gt;
  &lt;/div&gt;
  
  &lt;div&gt;
    &lt;span id="category-1"&gt;CatB&lt;/span&gt;
  
    &lt;ul&gt;
      &lt;li id="link-1-0"&gt;[..]&lt;/li&gt;
      &lt;li id="link-1-1"&gt;[..]&lt;/li&gt;
    &lt;/ul&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p><strong>Actual</strong> resulting ID's for LI:</p>
  
  <pre><code>&lt;div&gt;
    &lt;span id="category-0"&gt;CatA&lt;/span&gt;
  
    &lt;ul&gt;
      &lt;li id="link-0-0"&gt;[..]&lt;/li&gt;
      &lt;li id="link-1-1"&gt;[..]&lt;/li&gt;
      &lt;li id="link-2-2"&gt;[..]&lt;/li&gt;
    &lt;/ul&gt;
  &lt;/div&gt;
  
  &lt;div&gt;
    &lt;span id="category-1"&gt;CatB&lt;/span&gt;
  
    &lt;ul&gt;
      &lt;li id="link-0-0"&gt;[..]&lt;/li&gt;
      &lt;li id="link-1-1"&gt;[..]&lt;/li&gt;
    &lt;/ul&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>Can someone confirm this behaviour? Or did I miss something?</p>