title: JQuery :nth-child() append
body: <p>I have simple list:</p>
  
  <pre><code>&lt;ul&gt;
  &lt;li&gt;some text 1 &lt;/li&gt;
  &lt;li&gt;some text 2&lt;/li&gt;
  &lt;li&gt;some text 3&lt;/li&gt;
  &lt;li&gt;some text 4&lt;/li&gt;
  &lt;li&gt;some text 5&lt;/li&gt;
  &lt;li&gt;some text 6&lt;/li&gt;
  &lt;li&gt;some text 7&lt;/li&gt;
  &lt;/ul&gt;
  </code></pre>
  
  <p>I need add after each 4n element some div</p>
  
  <p>I have:</p>
  
  <pre><code>$("ul li:nth-child(4n)").after("&lt;div style='color:black'&gt;test&lt;/div&gt;");
  </code></pre>
  
  <p>But for example I have 4 elements and my div after it, and than I have only 3 element, but I need append my div after third element...How to make this?
  Thank you!</p>