alter Drupal 6 theme output after rendering with QueryPath

microformat.php

/**
 * Microformat function.
 */
function microformat() {
  $args = func_get_args();
  $hooks = array_shift($args);
  if (!is_array($hooks)) {
    $hooks = array($hooks);
  }
  $output = call_user_func_array('theme', array_merge(array($hooks), $args));
  if ($output) {
    include_once libraries_get_path('QueryPath') .'/QueryPath.php';
    $qp = hqp($output);
    foreach ($hooks as $hook) {
      drupal_alter('microformat_'. $hook, $qp, $args);
    }
    $output = $qp->xml();
  }
  return $output;
}

/**
 * A special-purpose version of {@link qp()} for Microformats.
 *
 * hqp means Microformat (μF) QueryPath.
 *
 * Output of Drupal themes (if valid XHTML) can be processed as XML snippets if
 * libxml is told to handle the document as HTML but the document is preceded
 * with an XML declaration, the document has a single root element and HTML
 * entities are replaced with UTF-8 encoded entities.
 *
 * The following options are automatically set unless overridden:
 *  - ignore_parser_warnings: TRUE
 *  - omit_xml_declaration: TRUE (on output, remove XML declaration)
 *  - use_parser: html
 *  - replace_entities: TRUE
 *
 * Parser warning messages are also suppressed, so if the parser emits a warning,
 * the application will not be notified. This is equivalent to
 * calling <code>@qp()</code>.
 *
 * Warning: Character set conversions will only work if the Multi-Byte (mb) library
 * is installed and enabled. This is usually enabled, but not always.
 *
 * @see qp()
 */
function hqp($document = NULL, $selector = NULL, $options = array(), $declaration = '<?xml version="1.0" encoding="UTF-8" ?>') {

  // Need a way to force an HTML parse instead of an XML parse when the
  // doctype is XHTML, since many XHTML documents are not valid XML
  // (because of coding errors, not by design).

  $options += array(
    'omit_xml_declaration' => TRUE,
    'ignore_parser_warnings' => TRUE,
    'use_parser' => 'html',
    'replace_entities' => TRUE,
  );
  return @qp($declaration . $document, $selector, $options);
}