title: Add child to xml with PHP simpleXml
body: <p>i have problem with simpleXml and adding new items. This is my xml:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;root&gt;
    &lt;items&gt;               
      &lt;item&gt;abc&lt;/item&gt;
      &lt;item&gt;def&lt;/item&gt;
      &lt;item&gt;ghi&lt;/item&gt;
  &lt;/items&gt;
  &lt;/root&gt;
  </code></pre>
  
  <p>Im using this php code:</p>
  
  <pre><code>$xml = simplexml_load_file("myxml.xml");
  $sxe = new SimpleXMLElement($xml-&gt;asXML());
  $newItem = $sxe-&gt;addChild("items");
  $newItem-&gt;addChild("item", $newValue);
  $sxe-&gt;asXML("myxml.xml"); 
  </code></pre>
  
  <p>This is the result:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
      &lt;root&gt;
        &lt;items&gt;               
          &lt;item&gt;abc&lt;/item&gt;
          &lt;item&gt;def&lt;/item&gt;
          &lt;item&gt;ghi&lt;/item&gt;
        &lt;/items&gt;
        &lt;items&gt;
          &lt;item&gt;jkl&lt;/item&gt;
        &lt;/items&gt;
      &lt;/root&gt;
  </code></pre>
  
  <p>This creates me new items node, but i want add item to the same already existing items node.</p>