title: using getElementById within popup opened by magnificPopup fails when trying access popup element
body: <p>Using getElementById fails, cause it tries to find the element with id "in" in the father HTML. How to get content of input element "id" from within the popup?     </p>
  
  <pre><code>&lt;html&gt;
  &lt;head&gt;
      &lt;link media="all" type="text/css" rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/magnific-popup.js/0.9.9/magnific-popup.css"&gt;
      &lt;script src="http://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"&gt;&lt;/script&gt;
          &lt;script src="//cdnjs.cloudflare.com/ajax/libs/magnific-popup.js/0.9.9/jquery.magnific-popup.min.js"&gt;&lt;/script&gt;
  &lt;/head&gt;
  &lt;body&gt;
      &lt;button id="someid"&gt;Open popup&lt;/button&gt;
  
  &lt;script&gt;
      $('#someid').magnificPopup({
                                            items: {
                                                src:  
                                                      '&lt;div class="white-popup"&gt;&lt;br&gt;\
                                                      &lt;input id="in" type="text" placeholder="content"&gt;\
                                                      &lt;a href=document.getElementById('in')&gt;Click&lt;/a&gt;',
  
                                                type: 'inline'
                                            }
                             });  
  &lt;/script&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>