title: zend specified doctype is malformed errord
body: <p>so I was trying to add the RDFA doctype into zend by typing the following into my layout.phtml...</p>
  
  <pre><code>$doctypeHelper = new Zend_View_Helper_Doctype();
  $doctypeHelper-&gt;doctype('XHTML1_RDFA');
  </code></pre>
  
  <p>so that I will be able to use the headMeta->appendProperty() function....but then it returned this error:</p>
  
  <pre><code>Fatal error: Uncaught exception 'Zend_View_Exception' with message 'The specified doctype is malformed'
  </code></pre>
  
  <p>how do I resolve this?</p>