title: PHP warning: Call-time pass-by-reference has been deprecated
body: <p>I am getting the warning: <code>Call-time pass-by-reference has been deprecated</code> for the following lines of code:</p>
  
  <pre><code>function XML() {
      $this-&gt;parser = &amp;xml_parser_create();
      xml_parser_set_option(&amp;$this-&gt;parser, XML_OPTION_CASE_FOLDING, false);
      xml_set_object(&amp;$this-&gt;parser, &amp;$this);
      xml_set_element_handler(&amp;$this-&gt;parser, 'open','close');
      xml_set_character_data_handler(&amp;$this-&gt;parser, 'data');
  }
  function destruct() {
      xml_parser_free(&amp;$this-&gt;parser);
  }
  function &amp; parse(&amp;$data) {
      $this-&gt;document = array();
      $this-&gt;stack    = array();
      $this-&gt;parent   = &amp;$this-&gt;document;
      return xml_parse(&amp;$this-&gt;parser, &amp;$data, true) ? $this-&gt;document : NULL;
  }
  </code></pre>
  
  <p>What does it cause and how to fix it?</p>