title: add custom tags to DOMDocument with php
body: <p>Maybe i am googling for the wrong keywords but is there not a way to add a custom tag so that DOMDocument can find custom tags. When i my html file i get lots of errors and of course getElementsByTagName returns nothing.</p>
  
  <pre><code>$dom = new DOMDocument();
  $html = $dom-&gt;loadHTMLFile('my html file');
  $dom-&gt;getElementsByTagName('un_welcome_text'); 
  </code></pre>
  
  <p>Does not fail.
  I realize this is not the best practice, but this code i have to parse is legacy stuff that can not change.</p>
  
  <p>the html looks like, an i have to get everything between </p>
  
  <pre><code> &lt;body&gt;
     &lt;u_top&gt;&lt;/u_top&gt;
        &lt;u_welcome_text&gt;
         A BUNCH OF HTML
        &lt;/u_welcome_text&gt;        
   &lt;/body&gt;
  </code></pre>