title: Child elements in webcomponent
body: <p>Suppose we have a custom element to use in this way: </p>
  
  <pre><code>&lt;list-image&gt;
      &lt;img src="" /&gt; 
       .... 
  &lt;/list-image&gt;
  </code></pre>
  
  <p>where list-image displays img tags in a slider way.
  If the user of component inserts an img tag with </p>
  
  <pre><code>document.querySelector('list-image').insertAdjacentHTML('beforeend', '&lt;img src="..." /&gt;');
  </code></pre>
  
  <p>is it possible for the component to know the new element img?</p>