title: Add elements to existing jQuery set
body: <p>Considering we have</p>
  
  <pre><code>let existingSet = $();
  </code></pre>
  
  <p>How are <code>newElements</code> added to that set by means of jQuery?</p>
  
  <pre><code>existingSet = existingSet.add(newElements);
  </code></pre>
  
  <p>is not an option, because I need the reference to this object. As well as <code>$.extend</code>, because <code>existingSet</code> may not be empty.</p>
  
  <p><a href="http://api.jquery.com/jquery.merge/" rel="nofollow">$.merge</a> documentation says that it accepts array-likes, but provides no further explanation of that, I'm not sure if it is suitable for jQuery objects.</p>