title: find first level children in nokogiri rails
body: <p>I've faced with a problem how to find first level children from the current element ?
  For example i have html :</p>
  
  <pre class="lang-html prettyprint-override"><code> &lt;table&gt;
     &lt;tr&gt;abc&lt;/tr&gt;
     &lt;tr&gt;def&lt;/tr&gt;   
     &lt;table&gt;
       &lt;tr&gt;second&lt;/tr&gt;
     &lt;/table&gt;
   &lt;/table&gt;
  </code></pre>
  
  <p>I am using Nokogiri for rails :  </p>
  
  <pre><code>table = page.css('table')
  table.css('tr')
  </code></pre>
  
  <p>It returns all <code>tr</code> inside <code>table</code>.
  But I need only 2 that first level for the table.</p>